BEGIN:VCALENDAR VERSION:2.0 PRODID:-//18.83.4.138//NONSGML kigkonsult.se iCalcreator 2.20// CALSCALE:GREGORIAN METHOD:PUBLISH X-FROM-URL:http://oceans.mit.edu X-WR-TIMEZONE:America/New_York BEGIN:VTIMEZONE TZID:America/New_York X-LIC-LOCATION:America/New_York BEGIN:STANDARD DTSTART:20171105T020000 TZOFFSETFROM:-0400 TZOFFSETTO:-0500 RDATE:20181104T020000 TZNAME:EST END:STANDARD BEGIN:DAYLIGHT DTSTART:20180311T020000 TZOFFSETFROM:-0500 TZOFFSETTO:-0400 TZNAME:EDT END:DAYLIGHT END:VTIMEZONE BEGIN:VEVENT UID:h4sofbi5ibsgevrin97kepp44k@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Abstract: A major question in how we approach climate change an d its impact on the carbon cycle is at what level of granularity must we u nderstand phytoplankton diversity. The phytoplankton that mediate CO2 upta ke in the marine biosphere are tremendously diverse\, non-homogeneously di stributed and oftentimes physiologically ill-characterized. Additionally\, they live among non-photosynthetic microbes from the three domains of lif e – creating a complex network of chemical exchanges and physical interact ions. Microbial oceanographers frequently employ genome and environmental sequence analyses to tackle these topics\, and yet many genes and features of genomes expressed in nature are of unknown function. By investigating this material in the lab and field we are discovering key\, previously uni dentified environmental controls and responses of phytoplankton as well as distributional information. Here\, we will explore phytoplankton diversit y and factors for bloom development at three levels of granularity – basic growth requirements in the context of microbial networks (in this case vi tamins)\, evolutionary divergence (in connection to nutrient limitation)\, and population connectivity through deep ocean currents (using repetitive \, gene-interrupting sequences). Through iterative modeling\, lab\, and fi eld experiments it should be possible to test and integrate ecologically r elevant levels of microbial diversity to understand primary production in transitioning ecosystems. DTSTART;TZID=America/New_York:20150506T121000 DTEND;TZID=America/New_York:20150506T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Alex Worden (Monterey Bay Aquarium Research Institute) Phytop lankton\, microbial networks and the global carbon cycle URL:http://oceans.mit.edu/event/sls-alex-worden-monterey-bay-aquarium-resea rch-institute-phytoplankton-microbial-networks-and-the-global-carbon-cycle X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nAbstract: A majo r question in how we approach climate change and its impact on the carbon cycle is at what level of granularity must we understand phytoplankton div ersity. The phytoplankton that mediate CO2 uptake in the marine biosphere are tremendously diverse\, non-homogeneously distributed and oftentimes ph ysiologically ill-characterized. Additionally\, they live among non-photos ynthetic microbes from the three domains of life – creating a complex netw ork of chemical exchanges and physical interactions. Microbial oceanograph ers frequently employ genome and environmental sequence analyses to tackle these topics\, and yet many genes and features of genomes expressed in na ture are of unknown function. By investigating this material in the lab an d field we are discovering key\, previously unidentified environmental con trols and responses of phytoplankton as well as distributional information . Here\, we will explore phytoplankton diversity and factors for bloom dev elopment at three levels of granularity – basic growth requirements in the context of microbial networks (in this case vitamins)\, evolutionary dive rgence (in connection to nutrient limitation)\, and population connectivit y through deep ocean currents (using repetitive\, gene-interrupting sequen ces). Through iterative modeling\, lab\, and field experiments it should b e possible to test and integrate ecologically relevant levels of microbial diversity to understand primary production in transitioning ecosystems. END:VEVENT BEGIN:VEVENT UID:e0lr5udf6dcsor5o2cbs9fui2o@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:The Antarctic Slope Front (ASF) almost completely encircles the Antarctic continent\, separating cold shelf waters from relatively warm C ircumpolar Deep Water (CDW) at mid-depth offshore. Exchanges across the AS F transport CDW toward marine-terminating glaciers\, and export Antarctic Bottom Water (AABW) to the abyssal ocean. Recent studies indicate that thi s exchange may be modulated by mesoscale eddies\, which facilitate cross-s lope exchanges via stirring along isopycnals and eddy bolus transports. In this seminar I will discuss physical controls over the rates of cross-slo pe water mass exchange\, and examine the dynamical balances governing cros s-slope eddy transfer. \n\nI will first present a recently-developed eddy- resolving process model of the Antarctic continental shelf and slope. The model enforces realistic offshore ocean stratification over idealized shel f/slope bathymetry\, in order to provide a realistic representation of the water masses in a configuration that can be analyzed cleanly. The model f orcing includes a westward wind stress over the continental slope and buoy ancy loss on the continental shelf\, consistent with prevailing Antarctic easterly winds and brine rejection in coastal polynyas.\n\nI will use this model to explore the sources of eddy kinetic energy (EKE) over the contin ental slope\, and its resulting impact on the cross-slope transport of mas s and tracers. I will show that the upper-ocean dynamics resemble the Anta rctic Circumpolar Current\, with wind-driven northward shoaling of the pyc nocline resisted by baroclinic conversion of potential energy to EKE. By c ontrast\, close to the ocean bed (at the CDW/AABW interface) potential ene rgy is removed by both the wind-driven mean overturning and the generation of baroclinic eddies\, and is instead sourced from the buoyancy loss on t he continental shelf. This EKE source turns out to be sensitive to variati ons in the model surface forcing and bathymetry. Consequently\, relatively small changes in the forcing and geometry can produce a substantial rearr angement of the water mass pathways and volume transports across the conti nental slope. These findings suggest that shoreward eddy transport of CDW should be localized to a few favorable locations around the Antarctic shel f break\, and that future changes in the easterly wind strength or coastal polynya productivity could significantly alter the shoreward heat transpo rt and the properties of the outflowing AABW. DTSTART;TZID=America/New_York:20150513T121000 DTEND;TZID=America/New_York:20150513T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Andrew Stewart (UCLA) – Eddy transport and mixing across the Antarctic continental slope URL:http://oceans.mit.edu/event/sls-andrew-stewart-ucla-eddy-transport-and- mixing-across-the-antarctic-continental-slope X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nThe Antarctic Sl ope Front (ASF) almost completely encircles the Antarctic continent\, sepa rating cold shelf waters from relatively warm Circumpolar Deep Water (CDW) at mid-depth offshore. Exchanges across the ASF transport CDW toward mari ne-terminating glaciers\, and export Antarctic Bottom Water (AABW) to the abyssal ocean. Recent studies indicate that this exchange may be modulated by mesoscale eddies\, which facilitate cross-slope exchanges via stirring along isopycnals and eddy bolus transports. In this seminar I will discus s physical controls over the rates of cross-slope water mass exchange\, an d examine the dynamical balances governing cross-slope eddy transfer. \n\n I will first present a recently-developed eddy-resolving process model of the Antarctic continental shelf and slope. The model enforces realistic of fshore ocean stratification over idealized shelf/slope bathymetry\, in ord er to provide a realistic representation of the water masses in a configur ation that can be analyzed cleanly. The model forcing includes a westward wind stress over the continental slope and buoyancy loss on the continenta l shelf\, consistent with prevailing Antarctic easterly winds and brine re jection in coastal polynyas.\n\nI will use this model to explore the sourc es of eddy kinetic energy (EKE) over the continental slope\, and its resul ting impact on the cross-slope transport of mass and tracers. I will show that the upper-ocean dynamics resemble the Antarctic Circumpolar Current\, with wind-driven northward shoaling of the pycnocline resisted by barocli nic conversion of potential energy to EKE. By contrast\, close to the ocea n bed (at the CDW/AABW interface) potential energy is removed by both the wind-driven mean overturning and the generation of baroclinic eddies\, and is instead sourced from the buoyancy loss on the continental shelf. This EKE source turns out to be sensitive to variations in the model surface fo rcing and bathymetry. Consequently\, relatively small changes in the forci ng and geometry can produce a substantial rearrangement of the water mass pathways and volume transports across the continental slope. These finding s suggest that shoreward eddy transport of CDW should be localized to a fe w favorable locations around the Antarctic shelf break\, and that future c hanges in the easterly wind strength or coastal polynya productivity could significantly alter the shoreward heat transport and the properties of t he outflowing AABW. END:VEVENT BEGIN:VEVENT UID:fifj494qb1lu2nt5j49v9jala0@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Abstract: Fixed nitrogen availability can regulate atmospheric carbon dioxide concentrations and climate as a whole. Its loss via two ana erobic microbial processes – anammox and denitrification – only occurs whe re oxygen is sufficiently depleted. Field experiments in the tropical Paci fic oxygen minimum zone resolve two long-standing debates critical to unde rstanding global climate. While very low oxygen concentrations are require d for fixed nitrogen loss by either anammox or denitrification\, organic m atter quantity and quality determine the magnitudes of these rates and the partitioning between the two pathways. Dissolved oxygen concentrations al so decouple the denitrification steps\, allowing for net production of nit rous oxide and accentuating the importance of the oxygen and nitrogen cycl es in regulating climate. DTSTART;TZID=America/New_York:20150514T133000 DTEND;TZID=America/New_York:20150514T143000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Andrew Babbin (MIT) Anaerobic cycling of marine nitrogen URL:http://oceans.mit.edu/event/sls-andrew-babbin-mit-anaerobic-cycling-of- marine-nitrogen X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nAbstract: Fixed nitrogen availability can regulate atmospheric carbon dioxide concentratio ns and climate as a whole. Its loss via two anaerobic microbial processes – anammox and denitrification – only occurs where oxygen is sufficiently d epleted. Field experiments in the tropical Pacific oxygen minimum zone res olve two long-standing debates critical to understanding global climate. W hile very low oxygen concentrations are required for fixed nitrogen loss b y either anammox or denitrification\, organic matter quantity and quality determine the magnitudes of these rates and the partitioning between the t wo pathways. Dissolved oxygen concentrations also decouple the denitrifica tion steps\, allowing for net production of nitrous oxide and accentuating the importance of the oxygen and nitrogen cycles in regulating climate. END:VEVENT BEGIN:VEVENT UID:g3ehmberbdu54vh6631pnu10ug@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Abstract: During the termination of the last ice age\, atmosphe ric CO2 increased by ~30% and global temperature rose by several degrees\, yet the mechanism(s) driving these major changes remain elusive. Marine a nd terrestrial records indicate that the amount of CO2 stored in the deep sea is greater during glacial periods than interglacial periods. The impli ed net transfer of carbon into and out of the ocean is likely the result o f changes in ocean circulation and/or the efficiency of the biologic pump. The resulting atmospheric CO2 fluctuations may play some role in amplifyi ng temperature shifts across ice age cycles. In this study\, we reconstruc t past variations in seawater carbonate ion concentration in order to gain insight into the relative roles of different oceanic CO2 storage mechanis ms and to place constraints on the timing\, magnitude\, and location of su bsequent deep ocean ventilation. Our reconstruction is based on the trace element and stable isotopic composition of calcite shells of the epi-benth ic foraminifer Cibicidoides wuellerstorfi from a sediment core in New Zeal and's Bay of Plenty. The sediment core site (1\,627 m water depth) lies wi thin the upper limit of modern Circumpolar Deep Water (CDW)\, ~500 m below the local Antarctic Intermediate Water (AAIW) salinity minimum. A record of ΔCO32- derived from the foraminiferal boron to calcium ratio (B/Ca) pro vides evidence for greater ice-age storage of respired CO2 and also reveal s abrupt deglacial shifts in inorganic carbon chemistry up to 30 µmol/kg ( 5 times larger than the difference between average LGM and Holocene values ). The rapidity of these deglacial changes in the ocean interior suggests 1) fluctuations in the intermediate-deep water boundary near the core site \, and/or 2) rapid changes in deep water composition. Additional records a re currently being reconstructed to probe these possibilities. DTSTART;TZID=America/New_York:20150520T121000 DTEND;TZID=America/New_York:20150520T130000 LOCATION:54 915 SEQUENCE:0 SUMMARY:SLS – Katherine Allen (Rutgers University) The Ocean’s Role in Endi ng an Ice Age: A View from the South Pacific URL:http://oceans.mit.edu/event/sls-katherine-allen-rutgers-university-the- oceans-role-in-ending-an-ice-age-a-view-from-the-south-pacific X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nAbstract: During the termination of the last ice age\, atmospheric CO2 increased by ~30% a nd global temperature rose by several degrees\, yet the mechanism(s) drivi ng these major changes remain elusive. Marine and terrestrial records indi cate that the amount of CO2 stored in the deep sea is greater during glaci al periods than interglacial periods. The implied net transfer of carbon i nto and out of the ocean is likely the result of changes in ocean circulat ion and/or the efficiency of the biologic pump. The resulting atmospheric CO2 fluctuations may play some role in amplifying temperature shifts acros s ice age cycles. In this study\, we reconstruct past variations in seawat er carbonate ion concentration in order to gain insight into the relative roles of different oceanic CO2 storage mechanisms and to place constraints on the timing\, magnitude\, and location of subsequent deep ocean ventila tion. Our reconstruction is based on the trace element and stable isotopic composition of calcite shells of the epi-benthic foraminifer Cibicidoides wuellerstorfi from a sediment core in New Zealand's Bay of Plenty. The se diment core site (1\,627 m water depth) lies within the upper limit of mod ern Circumpolar Deep Water (CDW)\, ~500 m below the local Antarctic Interm ediate Water (AAIW) salinity minimum. A record of ΔCO32- derived from the foraminiferal boron to calcium ratio (B/Ca) provides evidence for greater ice-age storage of respired CO2 and also reveals abrupt deglacial shifts i n inorganic carbon chemistry up to 30 µmol/kg (5 times larger than the dif ference between average LGM and Holocene values). The rapidity of these de glacial changes in the ocean interior suggests 1) fluctuations in the inte rmediate-deep water boundary near the core site\, and/or 2) rapid changes in deep water composition. Additional records are currently being reconstr ucted to probe these possibilities. END:VEVENT BEGIN:VEVENT UID:vvbkd9tl87kjotiqupdb4ao140@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION: DTSTART;TZID=America/New_York:20150527T121000 DTEND;TZID=America/New_York:20150527T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS URL:http://oceans.mit.edu/event/sls-4 END:VEVENT BEGIN:VEVENT UID:ff8acuj0ouic1ga8g808v7meo0@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION: DTSTART;TZID=America/New_York:20150603T121000 DTEND;TZID=America/New_York:20150603T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS URL:http://oceans.mit.edu/event/sls-3 END:VEVENT BEGIN:VEVENT UID:tjt8djodhuj2o0rs2n05q2ncn0@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:The abyssal ocean during the last glacial period is widely beli eved to have been\ncomparatively strongly salt stratified and close to the freezing point of sea water. Much\nof the support for that view is based on the work of McDuff\, Schrag\, Adkins\, M. Miller\nand several others wh o analyzed the chlorinity and oxygen isotope ratios from the pore\nwaters of deep sea cores. The data represent what\, in terms of control theory\, is termed a\n'terminal constraint'. That theoretical framework is used to revisit the inferences about\nthe LGM abyssal properties\, and in particul ar\, to understand the degree to which they are\nrobust to sometimes plaus ible assumptions about the data. DTSTART;TZID=America/New_York:20150916T121000 DTEND;TZID=America/New_York:20150916T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Carl Wunsch (MIT)- Salinity and Temperature of the Abyssal Oc ean at the Last Glacial Maximum (LGM) URL:http://oceans.mit.edu/event/sls-carl-wunsch-mit-salinity-and-temperatur e-of-the-abyssal-ocean-at-the-last-glacial-maximum-lgm X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nThe abyssal ocea n during the last glacial period is widely believed to have been\ncomparat ively strongly salt stratified and close to the freezing point of sea wate r. Much\nof the support for that view is based on the work of McDuff\, Sch rag\, Adkins\, M. Miller\nand several others who analyzed the chlorinity a nd oxygen isotope ratios from the pore\nwaters of deep sea cores. The data represent what\, in terms of control theory\, is termed a\n'terminal cons traint'. That theoretical framework is used to revisit the inferences abou t\nthe LGM abyssal properties\, and in particular\, to understand the degr ee to which they are\nrobust to sometimes plausible assumptions about the data. END:VEVENT BEGIN:VEVENT UID:sp1de2gn36rb15tpcgt2vona9k@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION: DTSTART;TZID=America/New_York:20150923T121000 DTEND;TZID=America/New_York:20150923T131000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Trevor McDougall (UNSW) – The thermodynamics of the turbulent ocean and of ice\; what we know and what things are still a puzzle URL:http://oceans.mit.edu/event/sls-trevor-mcdougall-unsw-the-thermodynamic s-of-the-turbulent-ocean-and-of-ice-what-we-know-and-what-things-are-still -a-puzzle END:VEVENT BEGIN:VEVENT UID:cro8mu7efln5cf3lqf30ma4u34@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:The Brazil Current (BC) is probably the least known and explored of the western boundary currents of the world ocean. In this tal k\, we offer a brief overview of the research carried out at the Oceanog raphic Institute of the University of São Paulo (IOUSP) on this current s ystem's general pattern\, water masses and meridionally changing vertic al structure. We focus here on the latitude range (21S­26S) at which the B C vertical structure very closely approaches the one predicted in the se minal work by Henry Stommel (1965). We explore the spatial­ temporal varia bility and conduct some first­order dynamical studies of this 'Stommeli an' BC by blending quasi­synoptic data sets\, mooring data and simple proc ess oriented modeling. DTSTART;TZID=America/New_York:20150930T121000 DTEND;TZID=America/New_York:20150930T131000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Ilson Carlos Almeida da Silveira (LaDO) – A “Stommelian” Br azil Current at 21S-26S: vertical structure and mesoscale variability URL:http://oceans.mit.edu/event/sls-ilson-carlos-almeida-da-silveira-lado-a -stommelian-brazil-current-at-21s-26s-vertical-structure-and-mesoscale-var iability X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nThe Brazil C urrent (BC) is probably the least known and explored of the western bo undary currents of the world ocean. In this talk\, we offer a brief overvi ew of the research carried out at the Oceanographic Institute of the Uni versity of São Paulo (IOUSP) on this current system's general pattern\ , water masses and meridionally changing vertical structure. We focus here on the latitude range (21S­26S) at which the BC vertical structure very closely approaches the one predicted in the seminal work by Henry Stommel (1965). We explore the spatial­ temporal variability and conduct some fi rst­order dynamical studies of this 'Stommelian' BC by blending quasi­sy noptic data sets\, mooring data and simple process oriented modeling.\n END:VEVENT BEGIN:VEVENT UID:hsqb5mfg6baavv7utsoo79kv20@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:With the explosion of exoplanet discoveries and atmospheric cha racterization over the last decade\, there is now the hope that in the nea r future\, it will be possible to study the atmospheres of low mass\, poss ibly Earthlike exoplanets. Interpreting these observations will be a grand challenge\, because the diversity of rocky planet climates is likely to b e enormous. Here I discuss the role that theory and idealized modeling can play in advancing our understanding of the possibilities. I present resul ts on two key problems in exoplanet climate evolution: the loss of a plane t’s water to space and the circulation (and possible nightside collapse) o f atmospheres on tidally locked planets. I show that in both cases\, scali ng analysis allows the fundamentals of the problem to be understood in a r obust and general way. I discuss the implications of these results for exo planet habitability and the future search for biosignatures by groundand s pacebased telescopes. DTSTART;TZID=America/New_York:20151007T121000 DTEND;TZID=America/New_York:20151007T131000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Robin Woodsworth (Harvard) – What can theory teach us about t he climates of low-mass exoplanets? URL:http://oceans.mit.edu/event/sls-robin-woodsworth-harvard-what-can-theor y-teach-us-about-the-climates-of-low-mass-exoplanets X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nWith the explosi on of exoplanet discoveries and atmospheric characterization over the last decade\, there is now the hope that in the near future\, it will be possi ble to study the atmospheres of low mass\, possibly Earthlike exoplanets. Interpreting these observations will be a grand challenge\, because the di versity of rocky planet climates is likely to be enormous. Here I discuss the role that theory and idealized modeling can play in advancing our unde rstanding of the possibilities. I present results on two key problems in e xoplanet climate evolution: the loss of a planet’s water to space and the circulation (and possible nightside collapse) of atmospheres on tidally lo cked planets. I show that in both cases\, scaling analysis allows the fund amentals of the problem to be understood in a robust and general way. I di scuss the implications of these results for exoplanet habitability and the future search for biosignatures by groundand spacebased telescopes. END:VEVENT BEGIN:VEVENT UID:q08g85divlio3s4ek47ihnfoog@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:In situ cosmogenic nuclides are produced in surface materials e xposed to cosmic radiation - cover a landscape with ice and production cea ses\; erode down into a landscape and nuclide concentrations quickly decre ase. We used these simple observations to explore a new proxy for reconstr ucting past ice sheet variability- the 10Be concentration of sand in marin e sediments adjacent to glaciated continents\, which should reflect the ex posure and erosion history on land before the sediment was deposited in th e deep sea. \nThis talk will present cosmogenic nuclide records from two O cean Drilling Program cores off east Greenland and the ANDRILL-1B core nex t to the East Antarctic Ice Sheet spanning the past 8 Myr\, as well as 10B e measurements on contemporary sediments emanating from the southern Green land Ice Sheet today. Notable features of the Greenland record include a 5 0-fold long-term decline in 10Be concentration reflecting late Cenozoic ic e-sheet growth\, pronounced 10Be dips coincident with major ice-rafted deb ris pulses\, considerable variability during the early Pleistocene\, and l ow concentrations indistinguishable from contemporary sediments throughout the past 1 Myr. The Antarctic record\, on the other hand\, exhibits very low 10Be concentrations over its entire length\, suggesting little to no s ubaerial exposure of land where the sediment was sourced from during the p ast 8 Myr. DTSTART;TZID=America/New_York:20151014T121000 DTEND;TZID=America/New_York:20151014T131000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Jeremy Shakun (Boston College)- Using cosmogenic isotopes in marine sediment cores to decipher long-term Greenland and Antarctic Ice Sh eet behavior URL:http://oceans.mit.edu/event/sls-jeremy-shakun-boston-college-using-cosm ogenic-isotopes-in-marine-sediment-cores-to-decipher-long-term-greenland-a nd-antarctic-ice-sheet-behavior X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nIn situ cosmogen ic nuclides are produced in surface materials exposed to cosmic radiation - cover a landscape with ice and production ceases\; erode down into a lan dscape and nuclide concentrations quickly decrease. We used these simple o bservations to explore a new proxy for reconstructing past ice sheet varia bility- the 10Be concentration of sand in marine sediments adjacent to gla ciated continents\, which should reflect the exposure and erosion history on land before the sediment was deposited in the deep sea. \nThis talk wil l present cosmogenic nuclide records from two Ocean Drilling Program cores off east Greenland and the ANDRILL-1B core next to the East Antarctic Ice Sheet spanning the past 8 Myr\, as well as 10Be measurements on contempor ary sediments emanating from the southern Greenland Ice Sheet today. Notab le features of the Greenland record include a 50-fold long-term decline in 10Be concentration reflecting late Cenozoic ice-sheet growth\, pronounced 10Be dips coincident with major ice-rafted debris pulses\, considerable v ariability during the early Pleistocene\, and low concentrations indisting uishable from contemporary sediments throughout the past 1 Myr. The Antarc tic record\, on the other hand\, exhibits very low 10Be concentrations ove r its entire length\, suggesting little to no subaerial exposure of land w here the sediment was sourced from during the past 8 Myr. END:VEVENT BEGIN:VEVENT UID:j02i76ignm8l356jekcpoq13i8@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Many aspects of how natural phytoplankton communities change th rough time remain poorly understood\, in large part because traditional or ganism-level sampling strategies are not amenable to high frequency\, long duration application. To overcome aspects of this limitation\, we develop ed the FlowCytobot series of automated submersible flow cytometers capable of rapid\, unattended analysis of individual plankton cells for long peri ods of time. FlowCytobot and Imaging FlowCytobot use a combination of lase r-based scattering and fluorescence measurements and video imaging of indi vidual particles to enumerate and characterize cells ranging from picocyan obacteria to chaining-forming diatoms. When combined with automated proces sing and image classification\, these observations make it possible to cha racterize taxonomic composition of plankton communities with unprecedented temporal resolution\, ranging from hours to years. Multi-year time series from FlowCytobot and Imaging FlowCytobot are now being used to study bloo m dynamics and community structure in US coastal waters. The high temporal resolution observations of single cell properties make it possible not on ly to characterize taxonomic composition and size structure\, but also to quantify taxon-specific growth rates. Emerging results provide a wide rang e of insights including links between climate factors and interannual vari ability in seasonal blooms\, decadal-scale shifts in community composition \, ecologically important roles for taxon-specific parasites\, and detecti on and characterization of harmful algal blooms. DTSTART;TZID=America/New_York:20151021T121000 DTEND;TZID=America/New_York:20151021T131000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Heidi Sosik (WHOI) – Bloom dynamics to climate change: Multi- scale observations of phytoplankton with autonomous flow cytometry URL:http://oceans.mit.edu/event/sls-heidi-sosik-whoi-bloom-dynamics-to-clim ate-change-multi-scale-observations-of-phytoplankton-with-autonomous-flow- cytometry X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nMany aspects of how natural phytoplankton communities change through time remain poorly un derstood\, in large part because traditional organism-level sampling strat egies are not amenable to high frequency\, long duration application. To o vercome aspects of this limitation\, we developed the FlowCytobot series o f automated submersible flow cytometers capable of rapid\, unattended anal ysis of individual plankton cells for long periods of time. FlowCytobot an d Imaging FlowCytobot use a combination of laser-based scattering and fluo rescence measurements and video imaging of individual particles to enumera te and characterize cells ranging from picocyanobacteria to chaining-formi ng diatoms. When combined with automated processing and image classificati on\, these observations make it possible to characterize taxonomic composi tion of plankton communities with unprecedented temporal resolution\, rang ing from hours to years. Multi-year time series from FlowCytobot and Imagi ng FlowCytobot are now being used to study bloom dynamics and community st ructure in US coastal waters. The high temporal resolution observations of single cell properties make it possible not only to characterize taxonomi c composition and size structure\, but also to quantify taxon-specific gro wth rates. Emerging results provide a wide range of insights including lin ks between climate factors and interannual variability in seasonal blooms\ , decadal-scale shifts in community composition\, ecologically important r oles for taxon-specific parasites\, and detection and characterization of harmful algal blooms.\n END:VEVENT BEGIN:VEVENT UID:vm82n0tt1i4ag6ja9dn5eut410@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Fjords form a key link in the climate system by connecting glac iers of the Greenland Ice Sheet to the ocean. They are the gateways for im porting oceanic heat to melt ice and for exporting meltwater into the ocea n. Submarine melting in fjords has been implicated as a driver of dynamic glacier changes in the past several decades. However\, there are no direct measurements of this melting\, and little is known about the fjord proces ses that modulate melt rates and export meltwater. Here\, we explore the d rivers of fjord circulation and heat transport in Sermilik Fjord\, near th e terminus of Helheim Glacier. We investigate the competing roles of buoya ncy forcing from the glacier and remote forcing from the shelf. Building o n estuarine studies of salt fluxes\, we assess the fluxes of heat and salt through the fjord and develop a new framework for inferring submarine mel t rates from glacial fjord budgets. DTSTART;TZID=America/New_York:20151028T121000 DTEND;TZID=America/New_York:20151028T131000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Rebecca Jackson (MIT/WHOI) – Ocean-glacier interactions in Gr eenland: fjord dynamics and heat transport URL:http://oceans.mit.edu/event/sls-rebecca-jackson-mitwhoi-ocean-glacier-i nteractions-in-greenland-fjord-dynamics-and-heat-transport X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nFjords form a ke y link in the climate system by connecting glaciers of the Greenland Ice S heet to the ocean. They are the gateways for importing oceanic heat to mel t ice and for exporting meltwater into the ocean. Submarine melting in fjo rds has been implicated as a driver of dynamic glacier changes in the past several decades. However\, there are no direct measurements of this melti ng\, and little is known about the fjord processes that modulate melt rate s and export meltwater. Here\, we explore the drivers of fjord circulation and heat transport in Sermilik Fjord\, near the terminus of Helheim Glaci er. We investigate the competing roles of buoyancy forcing from the glacie r and remote forcing from the shelf. Building on estuarine studies of salt fluxes\, we assess the fluxes of heat and salt through the fjord and deve lop a new framework for inferring submarine melt rates from glacial fjord budgets. END:VEVENT BEGIN:VEVENT UID:npqli52ji7mdgvlfa620c1bg58@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:During the daytime\, under conditions of relatively low winds a nd high solar insolation\, the nearsurface ocean warms. This stratified di urnal warm layer traps momentum from the wind near the surface\, generatin g shear across the layer. Horizontal advection associated with this diurna l warm layer shear is likely responsible for observed nearsurface fresheni ng in the upper meter of the ocean during the SPURSI field campaign.\n\nTh is shear associated with the diurnal warm layer\, a fractional depth of th e deeper mixed\nlayer\, horizontally displaces water near the surface duri ng the daytime converting horizontal gradients into vertical ones. At nigh t\, convection vertically mixes the horizontally displaced water throughou t the deeper mixed layer. This cycle of advection and then vertical mixing is a mechanism for effective submesoscale lateral diffusion on the scale of 110 km. We will discuss a simplified representation of the mechanism\, and estimates of effective submesoscale horizontal diffusivity for the mix ed layer. The calculated effective diffusivity associated with this mechan ism is 1100 m2/s\, depending on the advective timescale\, and depth and sp eed of the diurnal warm layer current.\n\nThe importance of the daily cycl e as a mechanism for smoothing lateral inhomogeneities within the mixed la yer will be considered. Additionally\, we examine how the advection associ ated with the diurnal warm layer may locally enhance or suppress the diurn al warming observed at a location. The frequency of occurrence of diurnal warm layers and global perspectives will be discussed. DTSTART;TZID=America/New_York:20151104T121000 DTEND;TZID=America/New_York:20151104T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Alec Bogdanoff (MIT/WHOI)- Submesoscale lateral mixing by diu rnal warm layer shear URL:http://oceans.mit.edu/event/sls-alec-bogdanoff-mitwhoi-submesoscale-lat eral-mixing-by-diurnal-warm-layer-shear X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nDuring the dayti me\, under conditions of relatively low winds and high solar insolation\, the nearsurface ocean warms. This stratified diurnal warm layer traps mome ntum from the wind near the surface\, generating shear across the layer. H orizontal advection associated with this diurnal warm layer shear is likel y responsible for observed nearsurface freshening in the upper meter of th e ocean during the SPURSI field campaign.\n\nThis shear associated with th e diurnal warm layer\, a fractional depth of the deeper mixed\nlayer\, hor izontally displaces water near the surface during the daytime converting h orizontal gradients into vertical ones. At night\, convection vertically m ixes the horizontally displaced water throughout the deeper mixed layer. T his cycle of advection and then vertical mixing is a mechanism for effecti ve submesoscale lateral diffusion on the scale of 110 km. We will discuss a simplified representation of the mechanism\, and estimates of effective submesoscale horizontal diffusivity for the mixed layer. The calculated ef fective diffusivity associated with this mechanism is 1100 m2/s\, dependin g on the advective timescale\, and depth and speed of the diurnal warm lay er current.\n\nThe importance of the daily cycle as a mechanism for smooth ing lateral inhomogeneities within the mixed layer will be considered. Add itionally\, we examine how the advection associated with the diurnal warm layer may locally enhance or suppress the diurnal warming observed at a lo cation. The frequency of occurrence of diurnal warm layers and global pers pectives will be discussed. END:VEVENT BEGIN:VEVENT UID:9g2sb4helvoome98emc9t6fva8@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:I will present a suite of records from a 950 m-depth sediment c ore from the western North Atlantic\, a site influenced by Antarctic Inter mediate Water (AAIW) in the modern ocean. The data suggest that northern s ourced waters dominated the water mass mixture during the LGM\, and that A AIW was shallower than ~850m. A d18O decrease early in Heinrich Stadial 1 (HS1) is attributed to the incorporation of deglacial meltwater into the n orthern sourced waters that continued to influence the site. Two interpret ations for the mid-to-late HS1 data will be discussed\, having opposite im plications for the vigor of the Atlantic Meridional Overturning Circulatio n (AMOC) during this interval. After HS1\, the data conform to the consens us view of AMOC variability – increased AAIW presence during the Bolling-A llerod and the Holocene\, when the AMOC was strong\, and reduced AAIW pres ence during the Younger Dryas when the AMOC was weak. DTSTART;TZID=America/New_York:20151118T120000 DTEND;TZID=America/New_York:20151118T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Delia Oppo (WHOI) – Deglacial Atlantic circulation:evidence f rom multiproxy records from shallow western north Atlantic sediment cores URL:http://oceans.mit.edu/event/sls-delia-oppo-whoi-deglacial-atlantic-circ ulationevidence-from-multiproxy-records-from-shallow-western-north-atlanti c-sediment-cores X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nI will present a suite of records from a 950 m-depth sediment core from the western North Atlantic\, a site influenced by Antarctic Intermediate Water (AAIW) in the modern ocean. The data suggest that northern sourced waters dominated the water mass mixture during the LGM\, and that AAIW was shallower than ~850 m. A d18O decrease early in Heinrich Stadial 1 (HS1) is attributed to the incorporation of deglacial meltwater into the northern sourced waters that continued to influence the site. Two interpretations for the mid-to-late HS1 data will be discussed\, having opposite implications for the vigor of the Atlantic Meridional Overturning Circulation (AMOC) during this interv al. After HS1\, the data conform to the consensus view of AMOC variability – increased AAIW presence during the Bolling-Allerod and the Holocene\, w hen the AMOC was strong\, and reduced AAIW presence during the Younger Dry as when the AMOC was weak. END:VEVENT BEGIN:VEVENT UID:8jlf3c11org5b01aqc8irt4u5g@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Diapycnal turbulent mixing in the Southern Ocean is believed to play a role in setting the rate of the ocean Meridional Overturning Circu lation (MOC)\, an important element of the global climate system. Whether this role is important\, however\, depends on the strength of this mixing\ , which remains poorly qualified on global scale. To address this question \, a passive tracer was released upstream of the Drake Passage in 2009 as a part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Oc ean (DIMES). While the mixing rates inferred from vertical dispersion of t he tracer are large and imply a key role played by mixing in setting the M OC\, those based on localized microstructure measurements seem to suggest otherwise. In this work we use a high resolution numerical model of the Dr ake Passage region\, sampled in the DIMES experiment and tuned to its obse rvations\, to explain that the difference between the two estimates arise from the large values of mixing encountered by the tracer when it flows cl ose to the bottom topography. We conclude that enhanced bottom mixing\, in combination with large lateral stirring and mixing by mesoscale eddies\, is sufficiently strong to play an important role in setting the Southern O cean branch of the MOC below 2 km. DTSTART;TZID=America/New_York:20151125T120000 DTEND;TZID=America/New_York:20151125T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Ali Mashayek (MIT) – Topographic Enhancement of Vertical Mixi ng in the Southern Ocean URL:http://oceans.mit.edu/event/sls-ali-mashayek-mit-topographic-enhancemen t-of-vertical-mixing-in-the-southern-ocean X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nDiapycnal turbul ent mixing in the Southern Ocean is believed to play a role in setting the rate of the ocean Meridional Overturning Circulation (MOC)\, an important element of the global climate system. Whether this role is important\, ho wever\, depends on the strength of this mixing\, which remains poorly qual ified on global scale. To address this question\, a passive tracer was rel eased upstream of the Drake Passage in 2009 as a part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). While the mixi ng rates inferred from vertical dispersion of the tracer are large and imp ly a key role played by mixing in setting the MOC\, those based on localiz ed microstructure measurements seem to suggest otherwise. In this work we use a high resolution numerical model of the Drake Passage region\, sample d in the DIMES experiment and tuned to its observations\, to explain that the difference between the two estimates arise from the large values of mi xing encountered by the tracer when it flows close to the bottom topograph y. We conclude that enhanced bottom mixing\, in combination with large lat eral stirring and mixing by mesoscale eddies\, is sufficiently strong to p lay an important role in setting the Southern Ocean branch of the MOC belo w 2 km. END:VEVENT BEGIN:VEVENT UID:e6rv273dmrbnm36gt5jtusdf8o@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Using a dynamically consistent state estimate\, the vertical re distribution of oceanic heat is investigated over a 20-year period (1992-2 011). The 20-year mean vertical heat flux shows strong variations both hor izontally and vertically\, consistent with the ocean being a dynamically a ctive and spatially complex heat exchanger. Between mixing and advection\, the two processes determining the vertical heat transport in the deep oce an\, advection plays a more important role in setting the spatial patterns of vertical heat exchange. The global integral of vertical heat flux show s an upward heat transport in the deep ocean\, suggesting an abyssal cooli ng trend over 1992-2011. \n\nThe bidecadal change of the ocean vertical h eat flux is also examined and provides dynamical insights into the global ocean heat content change. Preliminary results show that above 1500 m more heat is transported downward during 2002 2011 than 1992-2001. The spatial pattern of the vertical heat flux change shows consistent features with p revious studies\, such as more downward heat transport in the tropical Pac ific and the North Atlantic during the last decade. Whereas the spatial pa ttern of vertical heat flux change is closely related to the advection cha nge\, its global integral is largely determined by the change in mixing\, indicating a crucial role of ocean mixing in explaining the long-term chan ge of ocean vertical heat exchange. DTSTART;TZID=America/New_York:20151202T120000 DTEND;TZID=America/New_York:20151202T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Xinfeng Liang (MIT) – Global Ocean Vertical Heat Flux and It s Bidecadal URL:http://oceans.mit.edu/event/sls-xinfeng-liang-mit-global-ocean-vertical -heat-flux-and-its-bidecadal X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nUsing a dynamica lly consistent state estimate\, the vertical redistribution of oceanic hea t is investigated over a 20-year period (1992-2011). The 20-year mean vert ical heat flux shows strong variations both horizontally and vertically\, consistent with the ocean being a dynamically active and spatially complex heat exchanger. Between mixing and advection\, the two processes determin ing the vertical heat transport in the deep ocean\, advection plays a more important role in setting the spatial patterns of vertical heat exchange. The global integral of vertical heat flux shows an upward heat transport in the deep ocean\, suggesting an abyssal cooling trend over 1992-2011. \n\nThe bidecadal change of the ocean vertical heat flux is also examined and provides dynamical insights into the global ocean heat content change. Preliminary results show that above 1500 m more heat is transported downw ard during 2002 2011 than 1992-2001. The spatial pattern of the vertical h eat flux change shows consistent features with previous studies\, such as more downward heat transport in the tropical Pacific and the North Atlanti c during the last decade. Whereas the spatial pattern of vertical heat flu x change is closely related to the advection change\, its global integral is largely determined by the change in mixing\, indicating a crucial role of ocean mixing in explaining the long-term change of ocean vertical heat exchange. \n END:VEVENT BEGIN:VEVENT UID:depq9vqumhk21urf23fh7g7qbc@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:There is considerable interest in determining how the full dist ribution of surface temperature changes with warming. Model ensembles proj ect that extratropical land temperature variability will decrease in the f uture\, consistent with simple physical arguments related to polar amplifi cation. However\, observational studies have thus far come to conflicting conclusions. Several analytical pitfalls in interpreting observational rec ords lead to these discrepancies\, and highlight the importance of account ing for non-normality and the effects of filtering\, time-averaging\, grid ding\, and smoothing. I will present a set of methods designed to overcome these challenges\, which I apply to a large set of daily temperature obse rvations to show that a decrease in temperature variability is already rob ustly detectable in the extratropics. DTSTART;TZID=America/New_York:20151209T121000 DTEND;TZID=America/New_York:20151209T131000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS- – Andy Rhines (UofWashington) – Observations and Dynamics of Decreasing Variability of Winter Temperatures URL:http://oceans.mit.edu/event/sls-andy-rhines-uofwashington-observations- and-dynamics-of-decreasing-variability-of-winter-temperatures X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nThere is conside rable interest in determining how the full distribution of surface tempera ture changes with warming. Model ensembles project that extratropical land temperature variability will decrease in the future\, consistent with sim ple physical arguments related to polar amplification. However\, observati onal studies have thus far come to conflicting conclusions. Several analyt ical pitfalls in interpreting observational records lead to these discrepa ncies\, and highlight the importance of accounting for non-normality and t he effects of filtering\, time-averaging\, gridding\, and smoothing. I wil l present a set of methods designed to overcome these challenges\, which I apply to a large set of daily temperature observations to show that a dec rease in temperature variability is already robustly detectable in the ext ratropics. \n END:VEVENT BEGIN:VEVENT UID:f5lefkd12pr2nsoo70jpmp46ks@google.com DTSTAMP:20180503T075350Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:The Southern Ocean is one of the most energetic regions of the world ocean due to intense winds and storm forcing\, strong currents in th e form of the Antarctic Circumpolar Current (ACC) interacting with steep t opography\, and enhanced mesoscale activity. Consequently\, the Southern O cean is believed to be a hotspot for enhanced oceanic mixing. Previous wor k based on finestructure parameterizations has suggested that strong mixin g is also ubiquitous below the mixed layer. \n\nResults from a US/UK field program\, however\, showed that enhanced internal wave finestructure and turbulence levels are not widespread\, but limited to frontal zones where strong bottom currents collide with steep largeamplitude\ntopography. Dire ct measurements of turbulence showed that previous estimates of mixing rat es in the upper 1km are biased high by up to two orders of magnitude. Desp ite the prevalence of energetic wind events\, turbulence driven by downwar d propagating nearinertial wave shear is weak below the mixed layer. Ineff icient wind forcing at nearinertial frequencies and seasonally varying upp er ocean stratification likely contribute to the observed weak mixing rate s. Double diffusive processes and turbulence both contribute to buoyancy f lux\, elevating the effective mixing efficiency above the canonical value of 0.2 in the upper 1km. Ultimately\, this work informs largescale modelin g efforts through parameterizations of mixing processes in the highly unde rsampled Southern Ocean. DTSTART;TZID=America/New_York:20151216T121000 DTEND;TZID=America/New_York:20151216T131000 LOCATION:54-915 SEQUENCE:0 SUMMARY:Sophia Merrifield (MIT/WHOI) – Mechanisms for enhanced turbulence i n the Drake Passage region of the Southern Ocean URL:http://oceans.mit.edu/event/sophia-merrifield-mitwhoi-mechanisms-for-en hanced-turbulence-in-the-drake-passage-region-of-the-southern-ocean X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nThe Southern Oce an is one of the most energetic regions of the world ocean due to intense winds and storm forcing\, strong currents in the form of the Antarctic Cir cumpolar Current (ACC) interacting with steep topography\, and enhanced me soscale activity. Consequently\, the Southern Ocean is believed to be a ho tspot for enhanced oceanic mixing. Previous work based on finestructure pa rameterizations has suggested that strong mixing is also ubiquitous below the mixed layer. \n\nResults from a US/UK field program\, however\, showed that enhanced internal wave finestructure and turbulence levels are not w idespread\, but limited to frontal zones where strong bottom currents coll ide with steep largeamplitude\ntopography. Direct measurements of turbulen ce showed that previous estimates of mixing rates in the upper 1km are bia sed high by up to two orders of magnitude. Despite the prevalence of energ etic wind events\, turbulence driven by downward propagating nearinertial wave shear is weak below the mixed layer. Inefficient wind forcing at near inertial frequencies and seasonally varying upper ocean stratification lik ely contribute to the observed weak mixing rates. Double diffusive process es and turbulence both contribute to buoyancy flux\, elevating the effecti ve mixing efficiency above the canonical value of 0.2 in the upper 1km. Ul timately\, this work informs largescale modeling efforts through parameter izations of mixing processes in the highly undersampled Southern Ocean. END:VEVENT BEGIN:VEVENT UID:a2ekjra8t0jbckpkddqqo1uvm4@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Quantitative and mechanistic understanding of the changes in at mospheric CO2 concentrations and ocean carbon content between glacial and interglacial periods remains lacking. An increase in the efficiency of the biological pump has been hypothesized to contribute to higher ocean carbo n storage during glacial periods. Here we use a model of the ocean's bioge ochemical cycles that includes both carbon (13C) and nitrogen (15N) isotop es but no sediment interactions. We present results from one present day s imulation and six simulations of the Last Glacial Maximum (LGM\, ~20 ka be fore the present). The LGM simulations are idealized sensitivity experimen ts that explore effects of changes in maximum phytoplankton growth rates ( mmax). Increasing mmax in the model leads to a more efficient biological p ump\, more carbon storage\, and lower d13CDIC and oxygen concentrations. T he resulting increase of denitrification stimulates additional nitrogen fi xation and increases the spatial variance of d15NNO3\, while decreasing th e ocean’s fixed nitrogen inventory. Increased nitrogen fixation lowers sur face d15NNO3 in most of the tropics. In the model’s Southern Ocean modest increases in mmax result in higher d15NNO3 due to enhanced local nutrient utilization\, consistent with reconstructions\, but larger mmax cause decl ining values there owing to the poleward transport of low tropical d15NNO3 . Comparison to reconstructions from LGM sediments indicates that models w ith moderately increased mmax (by 16 - 33 %) fit both isotope data best\, whereas large increases are inconsistent with nitrogen isotopes although t hey still fit the carbon isotopes reasonably well. The best fitting models reproduce major features of the glacial d13CDIC\, d15N\, and oxygen recon structions\, while simulating reduced carbon storage\, compared with the p re-industrial ocean\, due to lower preformed carbon concentrations. We con clude that the biological pump was more efficient during the LGM. However\ , sediment interactions and whole ocean alkalinity changes may be required to increase ocean carbon storage. Our analysis illustrates interactions b etween the carbon and nitrogen cycles as well as the complementary constra ints provided by their isotopes. DTSTART;TZID=America/New_York:20160203T120000 DTEND;TZID=America/New_York:20160203T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Andreas Schmittner (Oregon State University) – Complementary Constraints from Carbon (13C) and Nitrogen (15N) Isotopes on the Efficienc y of the Glacial Ocean’s Biological Pump URL:http://oceans.mit.edu/event/sls-andreas-schmittner-oregon-state-univers ity-complementary-constraints-from-carbon-13c-and-nitrogen-15n-isotopes-on -the-efficiency-of-the-glacial-oceans-biological-pump X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nQuantitative and mechanistic understanding of the changes in atmospheric CO2 concentration s and ocean carbon content between glacial and interglacial periods remain s lacking. An increase in the efficiency of the biological pump has been h ypothesized to contribute to higher ocean carbon storage during glacial pe riods. Here we use a model of the ocean's biogeochemical cycles that inclu des both carbon (13C) and nitrogen (15N) isotopes but no sediment interact ions. We present results from one present day simulation and six simulatio ns of the Last Glacial Maximum (LGM\, ~20 ka before the present). The LGM simulations are idealized sensitivity experiments that explore effects of changes in maximum phytoplankton growth rates (mmax). Increasing mmax in t he model leads to a more efficient biological pump\, more carbon storage\, and lower d13CDIC and oxygen concentrations. The resulting increase of de nitrification stimulates additional nitrogen fixation and increases the sp atial variance of d15NNO3\, while decreasing the ocean’s fixed nitrogen in ventory. Increased nitrogen fixation lowers surface d15NNO3 in most of the tropics. In the model’s Southern Ocean modest increases in mmax result in higher d15NNO3 due to enhanced local nutrient utilization\, consistent wi th reconstructions\, but larger mmax cause declining values there owing to the poleward transport of low tropical d15NNO3. Comparison to reconstruct ions from LGM sediments indicates that models with moderately increased mm ax (by 16 - 33 %) fit both isotope data best\, whereas large increases are inconsistent with nitrogen isotopes although they still fit the carbon is otopes reasonably well. The best fitting models reproduce major features o f the glacial d13CDIC\, d15N\, and oxygen reconstructions\, while simulati ng reduced carbon storage\, compared with the pre-industrial ocean\, due t o lower preformed carbon concentrations. We conclude that the biological p ump was more efficient during the LGM. However\, sediment interactions and whole ocean alkalinity changes may be required to increase ocean carbon s torage. Our analysis illustrates interactions between the carbon and nitro gen cycles as well as the complementary constraints provided by their isot opes.\n END:VEVENT BEGIN:VEVENT UID:uksifljdddbbdn74o6ph44l3pk@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:The accuracy of ocean components of climate models is thought t o increase with resolution\, and we examine this associated change in util ity on a range of model fields. A 30-year integration (1978 to 2007) of th e NEMO model at 1o\, 1/4o and 1/12o is used to investigate the impact of m odelling choices associated with horizontal resolution. Changes in degrees of freedom associated with the increasing resolution allow alternative en ergy dissipation pathways and their impact is assessed.\n\nA distinct stre ngthening of the anti-clockwise component of the overturning is found in t he Southern Ocean\, primarily owing to the baroclinic component. The mixed layer does not change significantly with resolution\, with results compar able to observations. Minor changes with resolution are attributed to incr eased numbers of fronts with better resolution. In the interior\, steric h eight variability\, specifically its covariance between the surface (2000m ) does change owing to eddy effects not captured by the Gent-McWilliams pa rametrization. Topographic interactions are assessed in terms of vortex st retching in the bottom pressure torque term. Major changes are found in th e baroclinic component in the Southern Ocean. Low resolution appears appro priate for fields such as the mixed layer depth\, but higher resolution is increasingly required for large scale features through allowing eddy acti vity. DTSTART;TZID=America/New_York:20160210T120000 DTEND;TZID=America/New_York:20160210T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS- Maike Sonnewald (MIT) – Ocean model utility dependence on hori zontal resolution URL:http://oceans.mit.edu/event/sls-maike-sonnewald-mit-ocean-model-utility -dependence-on-horizontal-resolution X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nThe accuracy of ocean components of climate models is thought to increase with resolution\ , and we examine this associated change in utility on a range of model fie lds. A 30-year integration (1978 to 2007) of the NEMO model at 1o\, 1/4o a nd 1/12o is used to investigate the impact of modelling choices associated with horizontal resolution. Changes in degrees of freedom associated with the increasing resolution allow alternative energy dissipation pathways a nd their impact is assessed.\n\nA distinct strengthening of the anti-clock wise component of the overturning is found in the Southern Ocean\, primari ly owing to the baroclinic component. The mixed layer does not change sign ificantly with resolution\, with results comparable to observations. Minor changes with resolution are attributed to increased numbers of fronts wit h better resolution. In the interior\, steric height variability\, specifi cally its covariance between the surface (2000m) does change owing to eddy effects not captured by the Gent-McWilliams parametrization. Topographic interactions are assessed in terms of vortex stretching in the bottom pres sure torque term. Major changes are found in the baroclinic component in t he Southern Ocean. Low resolution appears appropriate for fields such as t he mixed layer depth\, but higher resolution is increasingly required for large scale features through allowing eddy activity. END:VEVENT BEGIN:VEVENT UID:8fmq0u02dfbgsq7o8fasosd454@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:We investigate how sea surface temperatures (SSTs) around Antar ctica respond to the Southern Annular Mode (SAM) on multiple timescales. T o that end we examine the relationship between SAM and SST within unforced preindustrial control simulations of coupled general circulation models ( GCMs) included in the Climate Modeling Intercomparison Project phase 5 (CM IP5). We develop a technique to extract the response of the Southern Ocean SST to a hypothetical step increase in the SAM index. We demonstrate that in many GCMs\, the expected SST step response function is nonmonotonic in time. Following a shift to a positive SAM anomaly\, an initial cooling re gime can transition into surface warming around Antarctica. However\, ther e are large differences across the CMIP5 ensemble. In some models the step response function never changes sign and cooling persists\, while in othe r GCMs the SST anomaly crosses over from negative to positive values only three years after a step increase in the SAM. This intermodel diversity ca n be related to differences in the models' climatological thermal ocean st ratification in the region of seasonal sea ice around Antarctica. Exploiti ng this relationship\, we use observational data for the time-mean meridio nal and vertical temperature gradients to constrain the real Southern Ocea n response to SAM on fast and slow timescales. DTSTART;TZID=America/New_York:20160217T120000 DTEND;TZID=America/New_York:20160217T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS- Yavor Kostov (MIT) – Fast and slow responses of Southern Ocean SST to SAM in coupled climate models URL:http://oceans.mit.edu/event/sls-yavor-kostov-mit-fast-and-slow-response s-of-southern-ocean-sst-to-sam-in-coupled-climate-models X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nWe investigate h ow sea surface temperatures (SSTs) around Antarctica respond to the Southe rn Annular Mode (SAM) on multiple timescales. To that end we examine the r elationship between SAM and SST within unforced preindustrial control simu lations of coupled general circulation models (GCMs) included in the Clima te Modeling Intercomparison Project phase 5 (CMIP5). We develop a techniqu e to extract the response of the Southern Ocean SST to a hypothetical step increase in the SAM index. We demonstrate that in many GCMs\, the expecte d SST step response function is nonmonotonic in time. Following a shift to a positive SAM anomaly\, an initial cooling regime can transition into su rface warming around Antarctica. However\, there are large differences acr oss the CMIP5 ensemble. In some models the step response function never ch anges sign and cooling persists\, while in other GCMs the SST anomaly cros ses over from negative to positive values only three years after a step in crease in the SAM. This intermodel diversity can be related to differences in the models' climatological thermal ocean stratification in the region of seasonal sea ice around Antarctica. Exploiting this relationship\, we u se observational data for the time-mean meridional and vertical temperatur e gradients to constrain the real Southern Ocean response to SAM on fast a nd slow timescales. END:VEVENT BEGIN:VEVENT UID:rpqjccranqb6v7lfuffo3h6rm4@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION: DTSTART;TZID=America/New_York:20160302T120000 DTEND;TZID=America/New_York:20160302T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS-Lorenzo Polvani (Columbia)- zone extremes in the Arctic\, and t heir impact on surface climate URL:http://oceans.mit.edu/event/sls-lorenzo-polvani-columbia-zone-extremes- in-the-arctic-and-their-impact-on-surface-climate END:VEVENT BEGIN:VEVENT UID:u24hh7d4d0vvru16l1rum83b1k@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:We describe and interpret in situ observations of tidally drive n turbulence that were obtained in the vicinity of a small channel that tr ansects the crest of the Mendocino Ridge in the north-eastern Pacific. Flo ws are funneled through the channel and have tidal excursion lengths compa rable to the width of the ridge crest. Once per day\, energetic turbulence is observed in the channel\, with overturns spanning almost half of the f ull water depth. A high resolution\, nonhydrostatic\, 2.5-dimensional simu lation is used to interpret the observations in terms of the advection of a breaking tidal lee wave past the site location\, and subsequent developm ent of a hydraulic jump. During this phase of the tide the strong transpor ts were associated with full depth flows\, however\, during the weaker bea t of the tide transports were shallow and surface-confined\, generating ne gligible turbulence. A regional numerical model of the area finds that the subinertial K1 (diurnal) tidal constituent generates topographically trap ped waves which propagate anticyclonically around the ridge\, and are asso ciated with enhanced near-topographic K1 transports. The interaction of th e trapped waves with the M2 (semidiurnal) surface tide produces a baroclin ic tidal flow that is alternately surface confined and full depth. Consist ent with observations\, full depth flows are associated with the generatio n of a large amplitude tidal lee wave on the northward face of the ridge\, while surface confined flows are largely nonturbulent. The regional model demonstrates that nearfield dissipation over the entire ridge is diurnall y modulated\, despite the larger amplitude of the M2 tidal constituent\, i ndicating that the trapped wave modulates near-field dissipation and mixin g at this location. DTSTART;TZID=America/New_York:20160309T120000 DTEND;TZID=America/New_York:20160309T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS- Ruth Musgrave (MIT-MechE) – Tidally driven mixing: breaking le e waves\, hydraulic jumps and the influence of subinertial trapped interna l tides URL:http://oceans.mit.edu/event/sls-ruth-musgrave-mit-meche-tidally-driven- mixing-breaking-lee-waves-hydraulic-jumps-and-the-influence-of-subinertial -trapped-internal-tides X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nWe describe and interpret in situ observations of tidally driven turbulence that were obta ined in the vicinity of a small channel that transects the crest of the Me ndocino Ridge in the north-eastern Pacific. Flows are funneled through the channel and have tidal excursion lengths comparable to the width of the r idge crest. Once per day\, energetic turbulence is observed in the channel \, with overturns spanning almost half of the full water depth. A high res olution\, nonhydrostatic\, 2.5-dimensional simulation is used to interpret the observations in terms of the advection of a breaking tidal lee wave p ast the site location\, and subsequent development of a hydraulic jump. Du ring this phase of the tide the strong transports were associated with ful l depth flows\, however\, during the weaker beat of the tide transports we re shallow and surface-confined\, generating negligible turbulence. A regi onal numerical model of the area finds that the subinertial K1 (diurnal) t idal constituent generates topographically trapped waves which propagate a nticyclonically around the ridge\, and are associated with enhanced near-t opographic K1 transports. The interaction of the trapped waves with the M2 (semidiurnal) surface tide produces a baroclinic tidal flow that is alter nately surface confined and full depth. Consistent with observations\, ful l depth flows are associated with the generation of a large amplitude tida l lee wave on the northward face of the ridge\, while surface confined flo ws are largely nonturbulent. The regional model demonstrates that nearfiel d dissipation over the entire ridge is diurnally modulated\, despite the l arger amplitude of the M2 tidal constituent\, indicating that the trapped wave modulates near-field dissipation and mixing at this location. \n END:VEVENT BEGIN:VEVENT UID:0ut5p5eqm7gvf41qhg299rrvf4@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Eddies in the ocean move westwards. Those shed by western bound ary currents must then interact with shelf-slope topography at the western boundary.\n\nThis simple picture is complicated by the presence of other eddies and mean flows\, but satellite observations show that many western boundary continental shelves are affected by mesoscale eddies translating near the shelfbreak. In this SST image\, a Gulf Stream Warm Core Ring (ant icyclone) transports cold fresh shelf water offshore across the Mid-Atlant ic Bight shelfbreak. Using idealized numerical simulations\, I address thr ee questions:\n\n1. Does the eddy always get to the shelfbreak\, or can sl oping topography stop an eddy from crossing it?\n2. What is the magnitude of offshore transport driven by these eddies?\n3. What is the effect of th e eddy on the shelf's flow field? DTSTART;TZID=America/New_York:20160316T120000 DTEND;TZID=America/New_York:20160316T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS- Deepak Cherian (MIT/WHOI) – Eddy vs. shelf-slope topography URL:http://oceans.mit.edu/event/sls-deepak-cherian-mitwhoi-eddy-vs-shelf-sl ope-topography X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nEddies in the oc ean move westwards. Those shed by western boundary currents must then inte ract with shelf-slope topography at the western boundary.\n\nThis simple p icture is complicated by the presence of other eddies and mean flows\, but satellite observations show that many western boundary continental shelve s are affected by mesoscale eddies translating near the shelfbreak. In thi s SST image\, a Gulf Stream Warm Core Ring (anticyclone) transports cold f resh shelf water offshore across the Mid-Atlantic Bight shelfbreak. Using idealized numerical simulations\, I address three questions:\n\n1. Does th e eddy always get to the shelfbreak\, or can sloping topography stop an ed dy from crossing it?\n2. What is the magnitude of offshore transport drive n by these eddies?\n3. What is the effect of the eddy on the shelf's flow field? END:VEVENT BEGIN:VEVENT UID:ofoqokjn4nk54q8ac5rmgrqbn4@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION: DTSTART;TZID=America/New_York:20160323T120000 DTEND;TZID=America/New_York:20160323T130000 SEQUENCE:0 SUMMARY:no SLS – Spring break URL:http://oceans.mit.edu/event/no-sls-spring-break-2 END:VEVENT BEGIN:VEVENT UID:vuc1onajs0fpct9nl84jltm95g@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Despite the major role played by mesoscale eddies in redistribu ting the energy of the large-scale circulation\, our understanding of thei r dissipation is still incomplete. This study investigates the generation of internal waves by decaying eddies in the North Atlantic western boundar y. The eddy presence and decay are measured from the altimetric surface re lative vorticity associated with an array of full-depth current meters ext ending ~100 km offshore at 26.5N. In addition\, internal waves are analyse d over a topographic rise from 2-year high-frequency measurements of an Ac oustic Doppler Current Profiler (ADCP)\, which is located 13 km offshore i n 600 m deep water. Despite an apparent polarity independence of the eddy decay observed from altimetric data\, the flow in the deepest 100 m is enh anced for anticyclones (25.2 cm/s) compared with cyclones (-4.7 cm/s). Acc ordingly\, the internal wave field is sensitive to this polarity-dependent deep velocity. This is apparent from the eddy-modulated enhanced dissipat ion rate\, which is obtained from a finescale parameterization and exceeds 10^-9 W/kg for near-bottom flows greater than 8 cm/s. The present study u nderlines the importance of oceanic western boundaries for removing the en ergy of low-mode westward-propagating eddies to higher-mode internal waves . DTSTART;TZID=America/New_York:20160330T120000 DTEND;TZID=America/New_York:20160330T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS-LOUIS CLEMENT (LDEO) – Generation of internal waves by eddies i mpinging on the western boundary of the North Atlantic URL:http://oceans.mit.edu/event/sls-louis-clement-ldeo-generation-of-intern al-waves-by-eddies-impinging-on-the-western-boundary-of-the-north-atlantic X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nDespite the majo r role played by mesoscale eddies in redistributing the energy of the larg e-scale circulation\, our understanding of their dissipation is still inco mplete. This study investigates the generation of internal waves by decayi ng eddies in the North Atlantic western boundary. The eddy presence and de cay are measured from the altimetric surface relative vorticity associated with an array of full-depth current meters extending ~100 km offshore at 26.5N. In addition\, internal waves are analysed over a topographic rise f rom 2-year high-frequency measurements of an Acoustic Doppler Current Prof iler (ADCP)\, which is located 13 km offshore in 600 m deep water. Despite an apparent polarity independence of the eddy decay observed from altimet ric data\, the flow in the deepest 100 m is enhanced for anticyclones (25. 2 cm/s) compared with cyclones (-4.7 cm/s). Accordingly\, the internal wav e field is sensitive to this polarity-dependent deep velocity. This is app arent from the eddy-modulated enhanced dissipation rate\, which is obtaine d from a finescale parameterization and exceeds 10^-9 W/kg for near-bottom flows greater than 8 cm/s. The present study underlines the importance of oceanic western boundaries for removing the energy of low-mode westward-p ropagating eddies to higher-mode internal waves. END:VEVENT BEGIN:VEVENT UID:7f8gqhpvh8tmioqalvkb0i486k@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:The ocean is populated by an intense geostrophic eddy field tha t is unresolved in most numerical ocean models used for climate prediction . A geometric framework for parameterising ocean eddy fluxes will be prese nted that is consistent with conservation of energy and momentum. The fram ework involves rewriting the residual-mean eddy force as the divergence of an eddy stress tensor. The magnitude of the eddy stress tensor is bounded by the eddy energy\, allowing its components to be rewritten in terms of the eddy energy and non-dimensional parameters describing the mean 'shape' of the eddies\, analogous to “eddy ellipses” used in observational oceano graphy. These non-dimensional geometric parameters have strong connections with classical stability theory\, for example\, the new framework preserv es the functional form of the linear Eady growth rate and\, with one addit ional ingredient\, Arnold’s first stability theorem. This framework also l eads to a simple model of 'eddy saturation”: the relative insensitivity of the ocean circulation and stratification to the magnitude of the surface wind stress in ocean models with explicit eddies. These results offer the prospect of improved eddy parameterisations that both preserve the underly ing symmetries and conservation laws inherent in the unfiltered equations\ , and reproduce empirical results that have been obtained with eddy-permit ting models. DTSTART;TZID=America/New_York:20160406T120000 DTEND;TZID=America/New_York:20160406T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS-David Marshall (Oxford) – A geometric interpretation of eddy-me an flow interaction in the ocean URL:http://oceans.mit.edu/event/sls-david-marshall-oxford-a-geometric-inter pretation-of-eddy-mean-flow-interaction-in-the-ocean X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nThe ocean is pop ulated by an intense geostrophic eddy field that is unresolved in most num erical ocean models used for climate prediction. A geometric framework for parameterising ocean eddy fluxes will be presented that is consistent wit h conservation of energy and momentum. The framework involves rewriting th e residual-mean eddy force as the divergence of an eddy stress tensor. The magnitude of the eddy stress tensor is bounded by the eddy energy\, allow ing its components to be rewritten in terms of the eddy energy and non-dim ensional parameters describing the mean 'shape' of the eddies\, analogous to “eddy ellipses” used in observational oceanography. These non-dimension al geometric parameters have strong connections with classical stability t heory\, for example\, the new framework preserves the functional form of t he linear Eady growth rate and\, with one additional ingredient\, Arnold’s first stability theorem. This framework also leads to a simple model of ' eddy saturation”: the relative insensitivity of the ocean circulation and stratification to the magnitude of the surface wind stress in ocean models with explicit eddies. These results offer the prospect of improved eddy p arameterisations that both preserve the underlying symmetries and conserva tion laws inherent in the unfiltered equations\, and reproduce empirical r esults that have been obtained with eddy-permitting models. END:VEVENT BEGIN:VEVENT UID:n46c0b7qi2hn84luvfnn1m0ho0@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:The ocean is a major sink of anthropogenic CO2 emissions. In or der to predict future atmospheric CO2 levels and global climate\, we must improve quantification of the ocean carbon pumps\, which sequester CO2 fro m the atmosphere on timescales from years to millennia. In this talk\, I w ill present field data from a quasi-Lagrangian cruise in Monterey Bay\, CA and use it to demonstrate how in situ measurements of dissolved gases can be used to quantify the biological and solubility pumps. In particular\, O2 concentration and isotopic composition are tracers of gross and net pro ductivity. A persistent challenge in quantifying biological productivity f rom O2 measurements is the need to accurately parameterize the physical pr ocesses that also alter O2 concentration and isotopic composition (e.g.\, bubble-mediated gas exchange\, diffusive gas exchange\, and mixing). Measu rements of multiple inert gases\, such as the noble gases\, are used to de velop parameterizations for these physical processes. These parameterizati ons are then applied to bioactive gases such as O2 and CO2\, thereby impro ving estimates of the ocean carbon pumps. Additionally\, I will compare in situ gas tracer methods for quantifying productivity with simultaneous in cubation- and sediment trap-based productivity estimates. DTSTART;TZID=America/New_York:20160413T120000 DTEND;TZID=America/New_York:20160413T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Cara Manning (MIT-WHOI) – What can oxygen and noble gases tea ch us about the ocean carbon pumps? URL:http://oceans.mit.edu/event/sls-cara-manning-mit-whoi-what-can-oxygen-a nd-noble-gases-teach-us-about-the-ocean-carbon-pumps X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nThe ocean is a m ajor sink of anthropogenic CO2 emissions. In order to predict future atmos pheric CO2 levels and global climate\, we must improve quantification of t he ocean carbon pumps\, which sequester CO2 from the atmosphere on timesca les from years to millennia. In this talk\, I will present field data from a quasi-Lagrangian cruise in Monterey Bay\, CA and use it to demonstrate how in situ measurements of dissolved gases can be used to quantify the bi ological and solubility pumps. In particular\, O2 concentration and isotop ic composition are tracers of gross and net productivity. A persistent cha llenge in quantifying biological productivity from O2 measurements is the need to accurately parameterize the physical processes that also alter O2 concentration and isotopic composition (e.g.\, bubble-mediated gas exchang e\, diffusive gas exchange\, and mixing). Measurements of multiple inert g ases\, such as the noble gases\, are used to develop parameterizations for these physical processes. These parameterizations are then applied to bio active gases such as O2 and CO2\, thereby improving estimates of the ocean carbon pumps. Additionally\, I will compare in situ gas tracer methods fo r quantifying productivity with simultaneous incubation- and sediment trap -based productivity estimates. END:VEVENT BEGIN:VEVENT UID:cvfe069npr1tlfqd734tmkb0o8@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:The talk will address the implications of a warming Arctic Ocea n to the structure and ventilation of the Arctic halocline\, and to the ov erlying sea-ice cover. In recent years\, atypically warm intrusions have been observed in the halocline. These derive from intense summertime solar warming on outcropping isopycnals in expansive ice-free regions. Heat tha t is stored in the shallow halocline can be released in the fall and winte r by shear driven mixing\, and convective mixing by the release of dense p lumes during sea-ice growth. On the other hand\, deeper warm ocean layers remain unaffected. I'll show that under continued warming\, there exists the possibility for a regime shift in halocline ventilation by these warm waters\, and a subsequent cap on the storage of deep-ocean heat. DTSTART;TZID=America/New_York:20160420T120000 DTEND;TZID=America/New_York:20160420T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Mary-Louise Timmermans (Yale) – Summer heat overwinters in th e Arctic Ocean URL:http://oceans.mit.edu/event/sls-mary-louise-timmermans-yale-summer-heat -overwinters-in-the-arctic-ocean X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nThe talk will ad dress the implications of a warming Arctic Ocean to the structure and vent ilation of the Arctic halocline\, and to the overlying sea-ice cover. In recent years\, atypically warm intrusions have been observed in the halocl ine. These derive from intense summertime solar warming on outcropping iso pycnals in expansive ice-free regions. Heat that is stored in the shallow halocline can be released in the fall and winter by shear driven mixing\, and convective mixing by the release of dense plumes during sea-ice growth . On the other hand\, deeper warm ocean layers remain unaffected. I'll sho w that under continued warming\, there exists the possibility for a regim e shift in halocline ventilation by these warm waters\, and a subsequent c ap on the storage of deep-ocean heat. END:VEVENT BEGIN:VEVENT UID:3c7gkt0bk76i6jrn78o4tjl8qc@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Recent work has shown that turbulence in the ocean due to break ing internal gravity is one of the largest uncertainties in climate models . Knowledge of the horizontal and vertical distribution of the turbulence is crucial\, which is challenging because internal waves can travel far f rom their sources and can break via a variety of mechanisms. In this talk I will first introduce internal waves for non-specialists\, then walk thr ough an example in the South China Sea where waves can be tracked from the ir source to their breaking locations\, and a rough energy budget determin ed. Then I’ll discuss recent progress in tracking internal wave energy fr om generation to cross-basin propagation to dissipation on the globe\, foc using on recent efforts to constrain 1) q\, the fraction of locally dissip ated energy and 2) the reflection coefficient which determines the partiti on of energy breaking over continental margins versus in the deep basins. A key thread of these analyses is the constant interplay between observat ions and high-resolution models. DTSTART;TZID=America/New_York:20160427T120000 DTEND;TZID=America/New_York:20160427T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Matthew Alford (Scripps Institute of Oceanography) – Observin g the generation\, propagation and dissipation of internal waves in the oc ean URL:http://oceans.mit.edu/event/sls-matthew-alford-scripps-institute-of-oce anography-observing-the-generation-propagation-and-dissipation-of-internal -waves-in-the-ocean X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nRecent work has shown that turbulence in the ocean due to breaking internal gravity is one of the largest uncertainties in climate models. Knowledge of the horizon tal and vertical distribution of the turbulence is crucial\, which is chal lenging because internal waves can travel far from their sources and can b reak via a variety of mechanisms. In this talk I will first introduce int ernal waves for non-specialists\, then walk through an example in the Sout h China Sea where waves can be tracked from their source to their breaking locations\, and a rough energy budget determined. Then I’ll discuss rece nt progress in tracking internal wave energy from generation to cross-basi n propagation to dissipation on the globe\, focusing on recent efforts to constrain 1) q\, the fraction of locally dissipated energy and 2) the refl ection coefficient which determines the partition of energy breaking over continental margins versus in the deep basins. A key thread of these anal yses is the constant interplay between observations and high-resolution mo dels. END:VEVENT BEGIN:VEVENT UID:dbe78mrro0f3pr2cs2afptun68@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION: DTSTART;TZID=America/New_York:20160504T120000 DTEND;TZID=America/New_York:20160504T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Stephanie Dutkiewicz – MIT (EAPS) URL:http://oceans.mit.edu/event/sls-stephanie-dutkiewicz-mit-eaps END:VEVENT BEGIN:VEVENT UID:086ehfu2ko34c7f70a5qn0m71k@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION: DTSTART;TZID=America/New_York:20160511T120000 DTEND;TZID=America/New_York:20160511T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Isabela Le Bras (MIT-WHOI) URL:http://oceans.mit.edu/event/sls-isabela-le-bras-mit-whoi END:VEVENT BEGIN:VEVENT UID:lgt54fubogv1d6gjt18ngh2f4o@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Does size matter for life in the ocean? DTSTART;TZID=America/New_York:20160513T120000 DTEND;TZID=America/New_York:20160513T130000 LOCATION:MIT 54-915 SEQUENCE:0 SUMMARY:SLS – Adrian Martin (NOCS) – Does size matter for life in the ocean ? URL:http://oceans.mit.edu/event/sls-adrian-martin-nocs-does-size-matter-for -life-in-the-ocean X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nDoes size matter for life in the ocean? END:VEVENT BEGIN:VEVENT UID:3dsmv53iq9qrj9rm821u916qvg@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Recent observations show that the Southern Ocean is dominating anthropogenic ocean heat uptake. Southern Ocean heat uptake is large becau se the strong northward transport of the heat content anomaly limits warmi ng of the sea surface temperature in the uptake region. Using results from eddy-rich global climate simulations\, I will discuss the processes contr olling the northward heat transport away from the uptake region and the co nvergence of the heat content anomaly in the midlatitude Southern Ocean. H eat budget analyses reveal that different processes dominate to the north and south of the main convergence region. The heat transport northward fro m the high-latitude uptake region is driven primarily by passive advection of the heat content anomaly by the existing time mean circulation\, with a smaller contribution from enhanced upwelling. The heat anomaly builds up in the midlatitudes due to a convergent Ekman transport anomaly\, combine d with limited heat transport further northward into the mode waters. To t he north of the peak convergence region\, eddy processes drive the warming and account for nearly 80% of the northward heat transport anomaly. DTSTART;TZID=America/New_York:20160525T120000 DTEND;TZID=America/New_York:20160525T125000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Adele Morrison (Princeton) – Mechanisms of Southern Ocean hea t uptake and transport URL:http://oceans.mit.edu/event/sls-adele-morrison-princeton-mechanisms-of- southern-ocean-heat-uptake-and-transport X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nRecent observati ons show that the Southern Ocean is dominating anthropogenic ocean heat up take. Southern Ocean heat uptake is large because the strong northward tra nsport of the heat content anomaly limits warming of the sea surface tempe rature in the uptake region. Using results from eddy-rich global climate s imulations\, I will discuss the processes controlling the northward heat t ransport away from the uptake region and the convergence of the heat conte nt anomaly in the midlatitude Southern Ocean. Heat budget analyses reveal that different processes dominate to the north and south of the main conve rgence region. The heat transport northward from the high-latitude uptake region is driven primarily by passive advection of the heat content anomal y by the existing time mean circulation\, with a smaller contribution from enhanced upwelling. The heat anomaly builds up in the midlatitudes due to a convergent Ekman transport anomaly\, combined with limited heat transpo rt further northward into the mode waters. To the north of the peak conver gence region\, eddy processes drive the warming and account for nearly 80% of the northward heat transport anomaly. END:VEVENT BEGIN:VEVENT UID:aaig83l8ph0piup82cpfhgudfk@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:We present a new\, steady-state macromolecule-based model to st udy light-nutrient co-limitation of phytoplankton growth. The model is bas ed on simplified metabolic flux network and resolves key pools of macro-mo lecules\, each of which has different roles for cellular growth. The model is used to predict and interpret the variation of cellular stoichiometry of fresh water Synechococcus sp. under different light and nutrient enviro nment over a range of dilution rates (averaged growth rates) in a steady s tate culture. The model explains the different response of cellular nitrog en and phosphorus quota to the various light-nutrient environments\, predi cting protein and RNA as most influential molecules on nitrogen and phosph orus quotas respectively. The model indicates that\, though total nitrogen storage is larger than phosphorus storage\, relative to requirements\, m any times more phosphorus can be stored. It accurately predicts the maximu m possible growth rate based on the limits of resource allocation within t he cell. Finally\, the model predicts nutrient-light co-limitation of cell population density under different dilution rates. While the nutrient has a direct effect on the population density\, light impacts it by modifying the cellular stoichiometry. This steady-state\, macromolecule based model provides bases for predicting phytoplankton growth in different dynamic e nvironments DTSTART;TZID=America/New_York:20160526T140000 DTEND;TZID=America/New_York:20160526T150000 SEQUENCE:0 SUMMARY:SLS – Keisuke Inomura (PAOC-MIT) – A macromolecular model of phytop lankton growth under light and nutrient co-limitation URL:http://oceans.mit.edu/event/sls-keisuke-inomura-paoc-mit-a-macromolecul ar-model-of-phytoplankton-growth-under-light-and-nutrient-co-limitation X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nWe present a new \, steady-state macromolecule-based model to study light-nutrient co-limit ation of phytoplankton growth. The model is based on simplified metabolic flux network and resolves key pools of macro-molecules\, each of which has different roles for cellular growth. The model is used to predict and int erpret the variation of cellular stoichiometry of fresh water Synechococcu s sp. under different light and nutrient environment over a range of dilut ion rates (averaged growth rates) in a steady state culture. The model exp lains the different response of cellular nitrogen and phosphorus quota to the various light-nutrient environments\, predicting protein and RNA as mo st influential molecules on nitrogen and phosphorus quotas respectively. T he model indicates that\, though total nitrogen storage is larger than pho sphorus storage\, relative to requirements\, many times more phosphorus c an be stored. It accurately predicts the maximum possible growth rate base d on the limits of resource allocation within the cell. Finally\, the mode l predicts nutrient-light co-limitation of cell population density under d ifferent dilution rates. While the nutrient has a direct effect on the pop ulation density\, light impacts it by modifying the cellular stoichiometry . This steady-state\, macromolecule based model provides bases for predict ing phytoplankton growth in different dynamic environments END:VEVENT BEGIN:VEVENT UID:ll80brjfgrjt197v2jusootht4@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION: DTSTART;TZID=America/New_York:20160527T120000 DTEND;TZID=America/New_York:20160527T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:Special SLS – Joe LaCasce (U of Oslo) – The buoyancy-driven ocean c irculation in idealized and realistic basins URL:http://oceans.mit.edu/event/special-sls-joe-lacasce-u-of-oslo-the-buoya ncy-driven-ocean-circulation-in-idealized-and-realistic-basins END:VEVENT BEGIN:VEVENT UID:37pufqcsb1t2cohqvog41humpc@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Internal hydraulic jumps in flows with upstream shear are inves tigated\, motivated by applications such as the flow over sills in Knight Inlet and Hood Canal. The role of upstream shear has not previously been thoroughly investigated\, although it is important in many natural flows\, including exchange flows and flows over topography. Several two-layer th eories are extended to include upstream shear\, showing that solutions onl y exist for a limited range of upstream shear values. More realistic two-d imensional numerical simulations are guided by the two-layer theory predic tions\, and the results are used to evaluate the theories. The simulations also show the qualitative types of hydraulic transitions that occur\, inc luding undular bores\, fully turbulent jumps\, and conjugate state-like so lutions. Numerical simulations are also used to investigate the mixing\, a nd a few 3D numerical simulations are found to be consistent with the 2D r esults.\n\nWhen the upstream shear is increased and the basic two-layer th eories no longer exhibit solutions\, entrainment is required. Furthermore\ , the downstream structure of the flow has an important effect on the jump properties. These factors are investigated by modifying a two-layer theor y to allow entrainment and account for the downstream vertical velocity st ructure. The resulting theory indicates that entrainment and jump structu re become important factors that influence the jump height. However\, the results are very sensitive to how the downstream vertical profiles of velo city and density are incorporated into the layered model\, highlighting th e limitations of the two-layer approximation when the shear is large.\n\nW hile these two layer theories provide insight into the types of jumps that can occur and the mixing that they cause\, jumps such as those that occur in Knight Inlet are significantly influenced by factors such as topograph y\, tidal forcing\, and three-dimensional effects. DTSTART;TZID=America/New_York:20160601T121000 DTEND;TZID=America/New_York:20160601T131000 LOCATION:54-915 SEQUENCE:0 SUMMARY:Kelly Anne Ogden (MIT-WHOI) – Internal Hydraulic Jumps with Upstrea m Shear URL:http://oceans.mit.edu/event/kelly-anne-ogden-mit-whoi-internal-hydrauli c-jumps-with-upstream-shear X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nInternal hydraul ic jumps in flows with upstream shear are investigated\, motivated by appl ications such as the flow over sills in Knight Inlet and Hood Canal. The role of upstream shear has not previously been thoroughly investigated\, a lthough it is important in many natural flows\, including exchange flows a nd flows over topography. Several two-layer theories are extended to incl ude upstream shear\, showing that solutions only exist for a limited range of upstream shear values. More realistic two-dimensional numerical simula tions are guided by the two-layer theory predictions\, and the results are used to evaluate the theories. The simulations also show the qualitative types of hydraulic transitions that occur\, including undular bores\, full y turbulent jumps\, and conjugate state-like solutions. Numerical simulati ons are also used to investigate the mixing\, and a few 3D numerical simul ations are found to be consistent with the 2D results.\n\nWhen the upstrea m shear is increased and the basic two-layer theories no longer exhibit so lutions\, entrainment is required. Furthermore\, the downstream structure of the flow has an important effect on the jump properties. These factors are investigated by modifying a two-layer theory to allow entrainment and account for the downstream vertical velocity structure. The resulting the ory indicates that entrainment and jump structure become important factors that influence the jump height. However\, the results are very sensitive to how the downstream vertical profiles of velocity and density are incorp orated into the layered model\, highlighting the limitations of the two-la yer approximation when the shear is large.\n\nWhile these two layer theori es provide insight into the types of jumps that can occur and the mixing t hat they cause\, jumps such as those that occur in Knight Inlet are signif icantly influenced by factors such as topography\, tidal forcing\, and thr ee-dimensional effects. END:VEVENT BEGIN:VEVENT UID:6107q6g88bcb157akgbn3j2qb8@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:The Antarctic shelf seas are at present receiving increasing am ounts of freshwater from the melting of the Antarctic Ice Sheet and its fr inging ice shelves. In response\, the surface ocean salinity in this regio n has declined. The talk will investigate the effects of the freshwater in put on regional sea level\, using satellite measurements of sea surface he ight (for months with no sea-ice cover) and a global ocean circulation mod el. It is found that from 1992 to 2011\, sea-level rise along the Antarcti c coast is at least 2 ± 0.8 mm yr−1 greater than the regional mean for the Southern Ocean. Further\, on the basis of the model simulations\, we conc lude that this sea-level rise is almost entirely related to steric adjustm ent\, rather than changes in local ocean mass\, with a halosteric rise in the upper ocean and thermosteric contributions at depth. DTSTART;TZID=America/New_York:20160719T121000 DTEND;TZID=America/New_York:20160719T131000 LOCATION:54-915 SEQUENCE:0 SUMMARY:Special SLS – Craig Rye CUSP (UK) – Trends in Antarctic Subpolar Se a Sea Level: Evidence of Increasing Glacial Melt? URL:http://oceans.mit.edu/event/special-sls-craig-rye-cusp-uk-trends-in-ant arctic-subpolar-sea-sea-level-evidence-of-increasing-glacial-melt X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nThe Antarctic sh elf seas are at present receiving increasing amounts of freshwater from th e melting of the Antarctic Ice Sheet and its fringing ice shelves. In resp onse\, the surface ocean salinity in this region has declined. The talk wi ll investigate the effects of the freshwater input on regional sea level\, using satellite measurements of sea surface height (for months with no se a-ice cover) and a global ocean circulation model. It is found that from 1 992 to 2011\, sea-level rise along the Antarctic coast is at least 2 ± 0.8 mm yr−1 greater than the regional mean for the Southern Ocean. Further\, on the basis of the model simulations\, we conclude that this sea-level ri se is almost entirely related to steric adjustment\, rather than changes i n local ocean mass\, with a halosteric rise in the upper ocean and thermos teric contributions at depth. END:VEVENT BEGIN:VEVENT UID:8fq7r97phuk895oaspp7ioq50s@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:El Ninõ–Southern Oscillation is here considered as large (time) scale phenomenon emerging from a complex and fast general dynamical syste m.\n\nThis seminar has two main goals. The first one is to give a physical ly reasonable explanation for the use of stochastic models for mimicking t he apparent random features of the El Ninõ–Southern Oscillation (ENSO) phe nomenon. The second one is to show how it is possible to obtain\, with the present approach\, some analytical results concerning the stationary dens ity function of the anomaly sea surface temperature\, and the occurring ti ming of strong El Ninõ events.\nThese results fit well the data from obser vations\, reproducing the asymmetry and the power law tail of the histogra ms of the NIÑO3 index and the timing of 2-7 years for intermediate El Ninõ events.\nThe approach is based on some of our recent theoretical results in the field of the dynamical origin of stochastic processes. More precise ly\, we apply this approach to the celebrated recharge oscillator model (R OM)\, weakly interacting by a multiplicative term with a general determini stic system (Madden-Julian Oscillations\, westerly wind burst\, etc.)\, an d we obtain a Fokker-Planck Equation that describes the statistical behavi or of the ROM.\n\nFor more details\n— M. Bianucci\, Geophysical Res. Lett. \, 43(1)\, 386-394 http://dx.doi.org/10.1002/2015GL066772\n— M. Bianucci\ , Journal of Statistical Mechanics: Theory and Experiment 2015\, P05016 (2 015)\, http://stacks.iop.org/1742-5468/2015/i=5/a=P05016\;\n— M. Bianucci\ , Int. Journal of Mod. Phys. B 0\, 1541004 (2015)\, http://www.worldscient ific.com/doi/abs/10.1142/S0217979215410040 DTSTART;TZID=America/New_York:20161005T120000 DTEND;TZID=America/New_York:20161005T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Marco Bianucci (ISMAR – CNR) – Modeling El Nino–Southern Osci llation: analytical results URL:http://oceans.mit.edu/event/sls-marco-bianucci-ismar-cnr-modeling-el-ni no-southern-oscillation-analytical-results X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nEl Ninõ–Southern Oscillation is here considered as large (time) scale phenomenon emerging from a complex and fast general dynamical system.\n\nThis seminar has two main goals. The first one is to give a physically reasonable explanation f or the use of stochastic models for mimicking the apparent random features of the El Ninõ–Southern Oscillation (ENSO) phenomenon. The second one is to show how it is possible to obtain\, with the present approach\, some an alytical results concerning the stationary density function of the anomaly sea surface temperature\, and the occurring timing of strong El Ninõ even ts.\nThese results fit well the data from observations\, reproducing the a symmetry and the power law tail of the histograms of the NIÑO3 index and t he timing of 2-7 years for intermediate El Ninõ events.\nThe approach is b ased on some of our recent theoretical results in the field of the dynamic al origin of stochastic processes. More precisely\, we apply this approach to the celebrated recharge oscillator model (ROM)\, weakly interacting by a multiplicative term with a general deterministic system (Madden-Julian Oscillations\, westerly wind burst\, etc.)\, and we obtain a Fokker-Planck Equation that describes the statistical behavior of the ROM.\n\nFor more details\n— M. Bianucci\, Geophysical Res. Lett.\, 43(1)\, 386-394 http:// dx.doi.org/10.1002/2015GL066772\n— M. Bianucci\, Journal of Statistical Me chanics: Theory and Experiment 2015\, P05016 (2015)\, http://stacks.iop.or g/1742-5468/2015/i=5/a=P05016\;\n— M. Bianucci\, Int. Journal of Mod. Phys . B 0\, 1541004 (2015)\, http://www.worldscientific.com/doi/abs/10.1142/S0 217979215410040 END:VEVENT BEGIN:VEVENT UID:er737t0tcc2jp3q2kbke0fbopc@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Ocean Property Fluxes: a Pseudo-Lagrangian Approach\n\nLagrangi an methods can provide insight into complex stirring and transport process es. These methods can provide a skeleton or template that allows one to id entify regions of rapid stirring\, transport\, and transport barriers. 'L obe dynamics'\, one of the most beautiful techniques in the toolbox\, prov ides for the measurement and visualization of transport and exchange acros s moving boundaries. Other methods allow for the identification of natura l barriers such as the material boundary of a coherent eddy. The focus is entirely on fluid 'material' transport (volume transport) and fluxes of o ceanographically important properties such as heat\, salt\, vorticity and chemical and biological tracers are relevant only to the extent that they are conserved following fluid motion. In addition\, lobe dynamics can bec ome cumbersome when the flow field is complex. I will talk about a genera lize approach that enables consideration of a variety of property fluxes\, provides a simplified application to complex flow fields\, and attempts t o preserves the beauty of the original approach. DTSTART;TZID=America/New_York:20161019T120000 DTEND;TZID=America/New_York:20161019T130000 LOCATION:54-209 SEQUENCE:0 SUMMARY:SLS – Larry Pratt (WHOI) URL:http://oceans.mit.edu/event/sls-larry-pratt-whoi X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nOcean Property F luxes: a Pseudo-Lagrangian Approach\n\nLagrangian methods can provide insi ght into complex stirring and transport processes. These methods can provi de a skeleton or template that allows one to identify regions of rapid sti rring\, transport\, and transport barriers. 'Lobe dynamics'\, one of the most beautiful techniques in the toolbox\, provides for the measurement an d visualization of transport and exchange across moving boundaries. Other methods allow for the identification of natural barriers such as the mate rial boundary of a coherent eddy. The focus is entirely on fluid 'materia l' transport (volume transport) and fluxes of oceanographically important properties such as heat\, salt\, vorticity and chemical and biological tra cers are relevant only to the extent that they are conserved following flu id motion. In addition\, lobe dynamics can become cumbersome when the flo w field is complex. I will talk about a generalize approach that enables consideration of a variety of property fluxes\, provides a simplified appl ication to complex flow fields\, and attempts to preserves the beauty of t he original approach. END:VEVENT BEGIN:VEVENT UID:0l8inq5v99j6i45p17dim1skj0@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Redox chemistry and ecological dynamics as underlying mechanism s for chemoautotrophic control of the primary nitrite maximum\n\nThe prima ry nitrite maximum (PNM) – the accumulation of nitrite at the base of the euphotic zone – is a ubiquitous but poorly understood oceanographic featur e. I will discuss how ecological dynamics and redox chemistry can explain the formation of the PNM by chemoautotrophic nitrifying microorganisms. Th eoretical descriptions of nitrifying metabolisms\, reflecting their underl ying redox chemistry\, results in the emergence of a PNM in a marine ecosy stem model. I also discuss the implications for understanding rates of new production using this more mechanistic representation of nitrification. DTSTART;TZID=America/New_York:20161026T120000 DTEND;TZID=America/New_York:20161026T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Emily Zakem (MIT) URL:http://oceans.mit.edu/event/sls-emily-zakem-mit X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nRedox chemistry and ecological dynamics as underlying mechanisms for chemoautotrophic cont rol of the primary nitrite maximum\n\nThe primary nitrite maximum (PNM) – the accumulation of nitrite at the base of the euphotic zone – is a ubiqui tous but poorly understood oceanographic feature. I will discuss how ecolo gical dynamics and redox chemistry can explain the formation of the PNM by chemoautotrophic nitrifying microorganisms. Theoretical descriptions of n itrifying metabolisms\, reflecting their underlying redox chemistry\, resu lts in the emergence of a PNM in a marine ecosystem model. I also discuss the implications for understanding rates of new production using this more mechanistic representation of nitrification.\n\n END:VEVENT BEGIN:VEVENT UID:loqqebtvf9gka4i5h01a0ujl90@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Scaling properties of Arctic sea ice deformation in high-resolu tion viscous-plastic sea ice models\n\nMany climate models use a rheology of the viscous-plastic type to simulate sea ice dynamics. With this rheolo gy\, large scale velocity and thickness fields can be realistically simula ted\, but the representation of small scale deformation rates and Linear K inematic Features (LKF) is thought to be inadequate. However\, at high res olution (< 5 km) the rheology starts to produce lines of localised deforma tion rates. In this study we use results from a 1-km Pan-Arctic model to i nvestigate the influence of these deformation features on the scaling prop erties of sea ice deformation. For evaluation the EGPS satellite data set of small-scale sea ice kinematics for the Central Arctic (successor of RGP S) is used.\nThe modelled sea ice deformation shows multi-fractal spatial scaling and\, in this sense\, agrees with the satellite data. In addition\ , the temporal coupling of the spatial scaling is reproduced as well. Furt hermore\, we examine the regional and seasonal variations of spatial scali ng properties and its dependence on the ice condition\, i.e. sea ice conce ntration and thickness\, which are in agreement with previous RGPS studies . DTSTART;TZID=America/New_York:20161031T150000 DTEND;TZID=America/New_York:20161031T160000 LOCATION:54-209 SEQUENCE:0 SUMMARY:SLS – Nils Hutter (Alfred Wegener Institute) URL:http://oceans.mit.edu/event/sls-nils-hutter-alfred-wegener-institute X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nScaling properti es of Arctic sea ice deformation in high-resolution viscous-plastic sea ic e models\n\nMany climate models use a rheology of the viscous-plastic type to simulate sea ice dynamics. With this rheology\, large scale velocity a nd thickness fields can be realistically simulated\, but the representatio n of small scale deformation rates and Linear Kinematic Features (LKF) is thought to be inadequate. However\, at high resolution (< 5 km) the rheolo gy starts to produce lines of localised deformation rates. In this study w e use results from a 1-km Pan-Arctic model to investigate the influence of these deformation features on the scaling properties of sea ice deformati on. For evaluation the EGPS satellite data set of small-scale sea ice kine matics for the Central Arctic (successor of RGPS) is used.\nThe modelled s ea ice deformation shows multi-fractal spatial scaling and\, in this sense \, agrees with the satellite data. In addition\, the temporal coupling of the spatial scaling is reproduced as well. Furthermore\, we examine the re gional and seasonal variations of spatial scaling properties and its depen dence on the ice condition\, i.e. sea ice concentration and thickness\, wh ich are in agreement with previous RGPS studies. END:VEVENT BEGIN:VEVENT UID:2mkb1gkqss0ulbueppk98dal4k@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION: DTSTART;TZID=America/New_York:20161109T120000 DTEND;TZID=America/New_York:20161109T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:Glenn Flierl (MIT) URL:http://oceans.mit.edu/event/glenn-flierl-mit END:VEVENT BEGIN:VEVENT UID:9qn6emngpg2i831ratfv3u8p14@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Deciphering deep ocean circulation changes between the present and the last glacial\n\nThe paleoclimate record indicates that the deep oc ean circulation and water masses have undergone major rearrangements betwe en glacial and interglacial climates\, which have likely played an importa nt role in the observed atmospheric carbon dioxide swings by affecting the partitioning of carbon between the atmosphere and ocean. The mechanisms b y which the deep ocean circulation changed\, however\, are still unclear a nd represent a major challenge to our understanding of past and future cli mates.\n\nWe address this question using a hierarchy of numerical models o f varying complexity\, ranging from a highly idealized ocean-only model to coupled climate simulations from the Paleoclimate Modelling Intercomparis on Project (PMIP). The results suggest that various inferred differences i n the deep ocean circulation and stratification between glacial and interg lacial climates can be attributed to increased Antarctic sea-ice formation in a colder world. Colder temperatures lead to thicker ice\, which is exp orted by winds. The associated increased freshwater export leads to saltie r and denser Antarctic Bottom Water\, consistent with high abyssal salinit ies inferred for the Last Glacial Maximum (LGM). The enhanced deep ocean s tratification moreover results in a weakening and shoaling of the inter-he mispheric overturning circulation\, again consistent with proxy evidence f or the LGM. \n\nThe results also highlight the importance to distinguish b etween the equilibrium and transient response of the ocean circulation to climatic changes. The adjustment of the deep ocean circulation is found to be highly non-monotonic\, with the response on centennial time-scales dif fering qualitatively from the equilibrium results. This distinction is rar ely observable in complex coupled climate models\, which cannot be integra ted for sufficiently long times. DTSTART;TZID=America/New_York:20161116T120000 DTEND;TZID=America/New_York:20161116T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Malte Jansen (University of Chicago) URL:http://oceans.mit.edu/event/sls-malte-jansen-university-of-chicago X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nDeciphering deep ocean circulation changes between the present and the last glacial\n\nThe paleoclimate record indicates that the deep ocean circulation and water m asses have undergone major rearrangements between glacial and interglacial climates\, which have likely played an important role in the observed atm ospheric carbon dioxide swings by affecting the partitioning of carbon bet ween the atmosphere and ocean. The mechanisms by which the deep ocean circ ulation changed\, however\, are still unclear and represent a major challe nge to our understanding of past and future climates.\n\nWe address this q uestion using a hierarchy of numerical models of varying complexity\, rang ing from a highly idealized ocean-only model to coupled climate simulation s from the Paleoclimate Modelling Intercomparison Project (PMIP). The resu lts suggest that various inferred differences in the deep ocean circulatio n and stratification between glacial and interglacial climates can be attr ibuted to increased Antarctic sea-ice formation in a colder world. Colder temperatures lead to thicker ice\, which is exported by winds. The associa ted increased freshwater export leads to saltier and denser Antarctic Bott om Water\, consistent with high abyssal salinities inferred for the Last G lacial Maximum (LGM). The enhanced deep ocean stratification moreover resu lts in a weakening and shoaling of the inter-hemispheric overturning circu lation\, again consistent with proxy evidence for the LGM. \n\nThe results also highlight the importance to distinguish between the equilibrium and transient response of the ocean circulation to climatic changes. The adjus tment of the deep ocean circulation is found to be highly non-monotonic\, with the response on centennial time-scales differing qualitatively from t he equilibrium results. This distinction is rarely observable in complex c oupled climate models\, which cannot be integrated for sufficiently long t imes. END:VEVENT BEGIN:VEVENT UID:a0cjs9f8f6q551t8rifnp5lb3c@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:The vertical structure of ocean eddies\n\nSince we began observ ing the ocean surface with satellites\, \nit's been of interest to underst and how the surface fields reflect motion\nat depth. A series of recent mo deling studies suggest the vertical structure \nis fairly well-captured by a single mode\, intensified near the surface and\ndecaying to zero with d epth. A study of 69 globally-distributed current \nmeters supports this\, in many locations outside of the tropics. The reason\nfor the dominance of a surface is explored theoretically\, using a simple\ntwo layer model. Th e latter predicts a wavenumber frequency spectra \nwhich resembles that in the ocean\, except at small scales. The latter are \nshown to be more lik ely to transfer energy to large scales\, leaving the\n(non-dispersive) lar ge scale waves in tact. A similar conclusion was made \npreviously from id ealized numerical experiments. DTSTART;TZID=America/New_York:20161122T120000 DTEND;TZID=America/New_York:20161122T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Joe Lacasce (University of Oslo) URL:http://oceans.mit.edu/event/sls-joe-lacasce-university-of-oslo X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nThe vertical str ucture of ocean eddies\n\nSince we began observing the ocean surface with satellites\, \nit's been of interest to understand how the surface fields reflect motion\nat depth. A series of recent modeling studies suggest the vertical structure \nis fairly well-captured by a single mode\, intensifie d near the surface and\ndecaying to zero with depth. A study of 69 globall y-distributed current \nmeters supports this\, in many locations outside o f the tropics. The reason\nfor the dominance of a surface is explored theo retically\, using a simple\ntwo layer model. The latter predicts a wavenum ber frequency spectra \nwhich resembles that in the ocean\, except at smal l scales. The latter are \nshown to be more likely to transfer energy to l arge scales\, leaving the\n(non-dispersive) large scale waves in tact. A s imilar conclusion was made \npreviously from idealized numerical experimen ts. \n END:VEVENT BEGIN:VEVENT UID:pk0iqfejbpehn1plfruqhpea5o@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Stability and Internal Flow Variability of Ice Sheets\n\nIce st reams are regions of fast-flowing ice embedded within ice sheets that acco unt for the majority of mass transport from ice sheet interiors to the oce an. Variability of ice stream flow on centennial to millennial time scales plays an important role in the present mass balance of the West Antarctic Ice Sheet. In this talk\, I show how a simple model of subglacial meltwat er production coupled to ice flow explains the underlying physical mechani sm for millennial-scale\, unforced ice stream variability and predicts the transition to steady ice stream flow. The model equally well reproduces m odern ice stream variability in the Siple Coast region of West Antarctica and Heinrich events\, periods of increased ice discharge from the Laurenti de Ice Sheet during the last glacial period. In a more realistic\, purpose -built model\, the same mechanism produces variability and rapid migration s of the ice stream grounding line. These migrations are always associated with mass imbalance near the grounding line\, but not necessarily in the ice stream at large\, which is important to consider when interpreting mod ern observations of grounding line variability. Under certain conditions\, this ice stream variability may cause the grounding line to slow down for hundreds to thousands of years even as it retreats onto a reverse bed slo pe\, before readvancing. Such behavior runs counter to the conventional th eories predicting the instability of ice sheets on reverse bed slopes. Det ermining if such behavior occurs in real ice sheets is important when eval uating the likelihood of irreversible ice sheet collapse and rapid sea lev el rise in the future. DTSTART;TZID=America/New_York:20161130T120000 DTEND;TZID=America/New_York:20161130T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Alexander Robel (California Institute of Technology & Univers ity of Chicago) URL:http://oceans.mit.edu/event/sls-alexander-robel X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nStability and In ternal Flow Variability of Ice Sheets\n\nIce streams are regions of fast-f lowing ice embedded within ice sheets that account for the majority of mas s transport from ice sheet interiors to the ocean. Variability of ice stre am flow on centennial to millennial time scales plays an important role in the present mass balance of the West Antarctic Ice Sheet. In this talk\, I show how a simple model of subglacial meltwater production coupled to ic e flow explains the underlying physical mechanism for millennial-scale\, u nforced ice stream variability and predicts the transition to steady ice s tream flow. The model equally well reproduces modern ice stream variabilit y in the Siple Coast region of West Antarctica and Heinrich events\, perio ds of increased ice discharge from the Laurentide Ice Sheet during the las t glacial period. In a more realistic\, purpose-built model\, the same mec hanism produces variability and rapid migrations of the ice stream groundi ng line. These migrations are always associated with mass imbalance near t he grounding line\, but not necessarily in the ice stream at large\, which is important to consider when interpreting modern observations of groundi ng line variability. Under certain conditions\, this ice stream variabilit y may cause the grounding line to slow down for hundreds to thousands of y ears even as it retreats onto a reverse bed slope\, before readvancing. Su ch behavior runs counter to the conventional theories predicting the insta bility of ice sheets on reverse bed slopes. Determining if such behavior o ccurs in real ice sheets is important when evaluating the likelihood of ir reversible ice sheet collapse and rapid sea level rise in the future.\n END:VEVENT BEGIN:VEVENT UID:5g6bl6kgr3mktf5110aik0lplk@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION: DTSTART;TZID=America/New_York:20161207T120000 DTEND;TZID=America/New_York:20161207T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS – Oliver Andrews (Tyndall Centre for Climate Change Research\, University of East Anglia) URL:http://oceans.mit.edu/event/sls-oliver-andrews-tyndall-centre-for-clima te-change-research-university-of-east-anglia END:VEVENT BEGIN:VEVENT UID:4976enni5i3j1pu5nflav90cs0@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Chasing Water: Lagrangian tracking of tracers\, plastic and pla nkton through the global ocean\n\n\n\nThe ocean is in constant motion\, wi th water circulating within and flowing between basins. As the water moves around\, it caries heat and nutrients\, as well as larger objects like pl anktonic organisms and litter around the globe.\n\nThe most natural way to study the pathways of water and the connections between ocean basins is u sing particle trajectories. The trajectories can come from either computin g of virtual floats in high-resolution ocean models\, or from the paths of free-flowing observational drifters (surface buoys or Argo floats) in the real ocean.\n\nIn this seminar\, I'll give an overview of some recent wor k with Lagrangian particles. I will show applications to dynamical oceanog raphy\, marine ecology\, palaeoclimatology and marine plastic pollution. C entral to each of these studies is the question on how connected the diffe rent ocean basins are\, and on what time scales water flows between the di fferent regions of the ocean. DTSTART;TZID=America/New_York:20170207T000000 DTEND;TZID=America/New_York:20170207T010000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS — Erik van Sebille (Imperial College London) URL:http://oceans.mit.edu/event/sls-erik-van-sebille-imperial-college-londo n X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nChasing Water: L agrangian tracking of tracers\, plastic and plankton through the global oc ean\n\n\n\nThe ocean is in constant motion\, with water circulating within and flowing between basins. As the water moves around\, it caries heat an d nutrients\, as well as larger objects like planktonic organisms and litt er around the globe.\n\nThe most natural way to study the pathways of wate r and the connections between ocean basins is using particle trajectories. The trajectories can come from either computing of virtual floats in high -resolution ocean models\, or from the paths of free-flowing observational drifters (surface buoys or Argo floats) in the real ocean.\n\nIn this sem inar\, I'll give an overview of some recent work with Lagrangian particles . I will show applications to dynamical oceanography\, marine ecology\, pa laeoclimatology and marine plastic pollution. Central to each of these stu dies is the question on how connected the different ocean basins are\, and on what time scales water flows between the different regions of the ocea n. END:VEVENT BEGIN:VEVENT UID:pjlef2grif27kg8g886drvn09k@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Warm-route versus cold-route interbasin exchange in the meridio nal overturning circulation - Why is the Atlantic saltier than the Pacific ?\n\nThe interbasin exchange of the meridional overturning circulation (MO C) is studied in an idealized domain with two basins connected by a circum polar channel in the southernmost region. Gnanadesikan’s (1999) conceptual model for the upper branch of the MOC is extended to include two basins o f different widths connected by a re-entrant channel at the southern edge and separated by two continents of different meridional extents. Its analy sis illustrates the basic processes of interbasin flow exchange either thr ough the connection at the southern latitude of the long continent (cold route) or through the connection at the southern latitude of the short con tinent (warm route). A cold-route exchange occurs when the short continent is poleward of the latitude separating the sub-polar and sub-tropical gyr e in the southern hemisphere\, otherwise there is warm-route exchange. The predictions of the conceptual model are compared to primitive equation co mputations in a domain with the same idealized geometry forced by wind-str ess\, surface temperature relaxation and surface salinity flux. A visualiz ation of the horizontal structure of the upper branch of the MOC illustrat es the cold and warm routes of interbasin exchange flows. Diagnostics of t he primitive equation computations show that the warm-route exchange flow is responsible for a substantial salinification of the basin where sinking occurs. This salinification is larger when the interbasin exchange is via the warm route\, and it is more pronounced when the warm-route exchange f lows from the wide to the narrow basin. DTSTART;TZID=America/New_York:20170301T120000 DTEND;TZID=America/New_York:20170301T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS — Paola Cessi (Scripps) URL:http://oceans.mit.edu/event/sls-paola-cessi X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nWarm-route versu s cold-route interbasin exchange in the meridional overturning circulation - Why is the Atlantic saltier than the Pacific?\n\nThe interbasin exchang e of the meridional overturning circulation (MOC) is studied in an idealiz ed domain with two basins connected by a circumpolar channel in the southe rnmost region. Gnanadesikan’s (1999) conceptual model for the upper branch of the MOC is extended to include two basins of different widths connecte d by a re-entrant channel at the southern edge and separated by two contin ents of different meridional extents. Its analysis illustrates the basic p rocesses of interbasin flow exchange either through the connection at the southern latitude of the long continent (cold route) or through the conne ction at the southern latitude of the short continent (warm route). A cold -route exchange occurs when the short continent is poleward of the latitud e separating the sub-polar and sub-tropical gyre in the southern hemispher e\, otherwise there is warm-route exchange. The predictions of the concept ual model are compared to primitive equation computations in a domain with the same idealized geometry forced by wind-stress\, surface temperature r elaxation and surface salinity flux. A visualization of the horizontal str ucture of the upper branch of the MOC illustrates the cold and warm routes of interbasin exchange flows. Diagnostics of the primitive equation compu tations show that the warm-route exchange flow is responsible for a substa ntial salinification of the basin where sinking occurs. This salinificatio n is larger when the interbasin exchange is via the warm route\, and it is more pronounced when the warm-route exchange flows from the wide to the n arrow basin.\n END:VEVENT BEGIN:VEVENT UID:lmlhi8pt0d9au0c0m4m7tg5ke0@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Barotropic turbulence above topography: form stress and eddy sa turation\n\nWind is an important driver of large-scale ocean currents\, im parting momentum into the ocean at the sea surface. This force is almost e ntirely balanced by topographic form stress (that is the correlation of bo ttom pressure and topographic slope). The direct effect of bottom or skin friction in turbulent boundary layers is almost negligible for the momentu m balance. We use a one-layer barotropic model to study the effect of a ra ndom monoscale bottom topography on beta-plane geostrophic turbulence. The model forcing is a uniform steady wind stress that produces both a unifor m large-scale flow and smaller-scale macroturbulence. The macroturbulence is characterized by both standing and transient eddies and the large-scale flow is retarded by a combination of bottom drag and domain-averaged topo graphic form stress produced by the standing eddies. \n\nA main control pa rameter is the ratio of beta to the root mean square gradient of the topog raphic potential vorticity (PV). We derive asymptotic scaling laws for the strength of the large-scale flow in the limiting cases of weak and strong forcing. If beta is comparable to\, or larger than\, the topographic PV g radient there is an “eddy saturation” regime in which the large-scale flow is insensitive to large changes in the wind stress. We show that eddy sat uration requires strong transient eddies that act effectively as PV diffus ion. This diffusion does not decrease the strength of the standing eddies but it does increase the topographic form stress by enhancing the correlat ion between topographic slope and the standing eddy pressure field. DTSTART;TZID=America/New_York:20170308T120000 DTEND;TZID=America/New_York:20170308T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS — William Young (Scripps) URL:http://oceans.mit.edu/event/sls-william-young X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nBarotropic turbu lence above topography: form stress and eddy saturation\n\nWind is an impo rtant driver of large-scale ocean currents\, imparting momentum into the o cean at the sea surface. This force is almost entirely balanced by topogra phic form stress (that is the correlation of bottom pressure and topograph ic slope). The direct effect of bottom or skin friction in turbulent bound ary layers is almost negligible for the momentum balance. We use a one-lay er barotropic model to study the effect of a random monoscale bottom topog raphy on beta-plane geostrophic turbulence. The model forcing is a uniform steady wind stress that produces both a uniform large-scale flow and smal ler-scale macroturbulence. The macroturbulence is characterized by both st anding and transient eddies and the large-scale flow is retarded by a comb ination of bottom drag and domain-averaged topographic form stress produce d by the standing eddies. \n\nA main control parameter is the ratio of bet a to the root mean square gradient of the topographic potential vorticity (PV). We derive asymptotic scaling laws for the strength of the large-scal e flow in the limiting cases of weak and strong forcing. If beta is compar able to\, or larger than\, the topographic PV gradient there is an “eddy s aturation” regime in which the large-scale flow is insensitive to large ch anges in the wind stress. We show that eddy saturation requires strong tra nsient eddies that act effectively as PV diffusion. This diffusion does no t decrease the strength of the standing eddies but it does increase the to pographic form stress by enhancing the correlation between topographic slo pe and the standing eddy pressure field.\n END:VEVENT BEGIN:VEVENT UID:282jnfvshnuoiapnbkcm8bf17g@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Southern Ocean eddies: generation\, propagation and decay\n\nTh e Southern Ocean has high concentrations of eddy kinetic energy\, but anal ysis of altimeter data and an ocean state estimate show that the generatio n of relatively large amplitude eddies is not a ubiquitous feature of the Southern Ocean but rather a phenomenon that is constrained to isolated\, w ell-defined regions. Five “hotspots” of high probability of eddy generatio n are identified using altimeter data. These hotspots are located downstre am of major topographic features\, with their boundaries closely following f/H contours. Eddies generated in these locations do not propagate far bu t decay within the boundaries of the generation area. The anisotropy of th e dispersion of eddy tracks in geographical coordinates versus a rotated c oordinates system aligned with f/H contours\, shows that eddies tend to fo llow f/H contours rather than f. Maps of buoyancy and shear production ter ms computed from a state estimation model show enhanced values of both con version terms inside the hotspots\, with buoyancy production two orders of magnitude larger than shear production. The mean potential density field estimated from Argo floats shows that inside the hotspots isopycnal slopes are steep\, indicating availability of potential energy and providing fur ther evidence of the main generation mechanism. The hotspots identified in this paper overlap with previously identified regions of standing meander s. We hypothesize that hotspot locations can be explained by the combined effect of topographic features\, standing meanders which enhanced baroclin ic instability and availability of potential energy to generate eddies via baroclinic instabilities. DTSTART;TZID=America/New_York:20170315T120000 DTEND;TZID=America/New_York:20170315T130000 SEQUENCE:0 SUMMARY:SLS — Uriel Zajaczkovski (Scripps) URL:http://oceans.mit.edu/event/sls-uriel-zajaczkovski X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nSouthern Ocean e ddies: generation\, propagation and decay\n\nThe Southern Ocean has high c oncentrations of eddy kinetic energy\, but analysis of altimeter data and an ocean state estimate show that the generation of relatively large ampli tude eddies is not a ubiquitous feature of the Southern Ocean but rather a phenomenon that is constrained to isolated\, well-defined regions. Five “ hotspots” of high probability of eddy generation are identified using alti meter data. These hotspots are located downstream of major topographic fea tures\, with their boundaries closely following f/H contours. Eddies gener ated in these locations do not propagate far but decay within the boundari es of the generation area. The anisotropy of the dispersion of eddy tracks in geographical coordinates versus a rotated coordinates system aligned w ith f/H contours\, shows that eddies tend to follow f/H contours rather th an f. Maps of buoyancy and shear production terms computed from a state es timation model show enhanced values of both conversion terms inside the ho tspots\, with buoyancy production two orders of magnitude larger than shea r production. The mean potential density field estimated from Argo floats shows that inside the hotspots isopycnal slopes are steep\, indicating ava ilability of potential energy and providing further evidence of the main g eneration mechanism. The hotspots identified in this paper overlap with pr eviously identified regions of standing meanders. We hypothesize that hots pot locations can be explained by the combined effect of topographic featu res\, standing meanders which enhanced baroclinic instability and availabi lity of potential energy to generate eddies via baroclinic instabilities. \n END:VEVENT BEGIN:VEVENT UID:gva7pvgq40gn82og8h8hrmoqug@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:High-resolution observations of internal wave induced turbulenc e in the deep ocean \n\nAn overview is presented of high-resolution temper ature observations above underwater topography in the deep\, generally sta bly stratified ocean. The Eulerian mooring technique is used to monitor te mperature variations by typically 100 sensors distributed over lines betwe en 40 and 400 m long. The independent sensors sample at a rate of 1 Hz for up to one year with a precision better than 0.1 mK. This precision and sa mpling rate are sufficient to resolve the large\, energy containing turbul ent eddies and all of the internal waves and their breaking above underwat er topography. Such underwater wave breaking is the key mechanism for the redistribution of nutrients and heat (to maintain the ocean stably stratif ied)\, and the resuspension of sediment.\n\nUnder conditions of tight temp erature-density relationship\, the temperature data are used to quantify t urbulent overturns. These observations show two distinctive turbulence pro cesses that are associated with different phases of a large-scale\, mainly tidal\, internal gravity wave: i) highly nonlinear turbulent bores during the upslope propagating phase\, and ii) Kelvin-Helmholtz billows\, at som e distance above the slope\, during the downslope phase. While the former may be associated in part with convective turbulent overturning following Rayleigh-Taylor instabilities\, the latter are mainly related to shear-ind uced instabilities. Under weaker stratified conditions\, away from boundar ies\, free convective mixing appears more often\, but a clear inertial sub range in temperature spectra is indicative of dominant shear-induced turbu lence. With stratification\, turbulence is seen to increase in dissipation rate and diffusivity all the way to the bottom\, which challenges the ide a of a homogeneous bottom boundary layer. With a newly developed five-line s mooring\, the transition from isotropy (full turbulence) to anisotropy ( stratified turbulence/internal waves) is revealed. DTSTART;TZID=America/New_York:20170405T120000 DTEND;TZID=America/New_York:20170405T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS — Hans van Haren (NIOZ) URL:http://oceans.mit.edu/event/sls-hans-van-haren X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nHigh-resolution observations of internal wave induced turbulence in the deep ocean \n\nAn overview is presented of high-resolution temperature observations above un derwater topography in the deep\, generally stably stratified ocean. The E ulerian mooring technique is used to monitor temperature variations by typ ically 100 sensors distributed over lines between 40 and 400 m long. The i ndependent sensors sample at a rate of 1 Hz for up to one year with a prec ision better than 0.1 mK. This precision and sampling rate are sufficient to resolve the large\, energy containing turbulent eddies and all of the i nternal waves and their breaking above underwater topography. Such underwa ter wave breaking is the key mechanism for the redistribution of nutrients and heat (to maintain the ocean stably stratified)\, and the resuspension of sediment.\n\nUnder conditions of tight temperature-density relationshi p\, the temperature data are used to quantify turbulent overturns. These o bservations show two distinctive turbulence processes that are associated with different phases of a large-scale\, mainly tidal\, internal gravity w ave: i) highly nonlinear turbulent bores during the upslope propagating ph ase\, and ii) Kelvin-Helmholtz billows\, at some distance above the slope\ , during the downslope phase. While the former may be associated in part w ith convective turbulent overturning following Rayleigh-Taylor instabiliti es\, the latter are mainly related to shear-induced instabilities. Under w eaker stratified conditions\, away from boundaries\, free convective mixin g appears more often\, but a clear inertial subrange in temperature spectr a is indicative of dominant shear-induced turbulence. With stratification\ , turbulence is seen to increase in dissipation rate and diffusivity all t he way to the bottom\, which challenges the idea of a homogeneous bottom b oundary layer. With a newly developed five-lines mooring\, the transition from isotropy (full turbulence) to anisotropy (stratified turbulence/inter nal waves) is revealed.\n END:VEVENT BEGIN:VEVENT UID:asmkr42urnv29bn7kehvf58q8s@google.com DTSTAMP:20180503T075351Z CATEGORIES;LANGUAGE=en-US:MIT Seminar | PAOC Oceanography and Climate Sack Lunch CONTACT: DESCRIPTION:Modeling iceberg drift and decay in modern and glacial climates \n\nUnder global warming\, the calving of icebergs into the polar oceans i s expected to increase. As a result\, the role that icebergs play in Earth 's climate system has received a recent surge of interest\, and efforts ar e underway to explicitly represent icebergs in GCMs. A better understandin g of how icebergs drift and decay will help facilitate an accurate represe ntation of icebergs and guide the interpretation of GCM results. In this t alk I will present an idealized analytical model that we developed to aid this effort. I will use the model to address (i) which climate model varia bles are most important to accurately model iceberg evolution and (ii) whe ther climate models do a good job simulating these variables. I then will turn to episodes of massive iceberg discharge\, called Heinrich Events\, w hich occurred during the last glacial period. These events are believed to have had large-scale impacts on the global climate system. However\, mode ling icebergs that lived and melted more than 10\,000 years ago comes with its own challenges\, as we will see. DTSTART;TZID=America/New_York:20170419T120000 DTEND;TZID=America/New_York:20170419T130000 LOCATION:54-915 SEQUENCE:0 SUMMARY:SLS — Till Wagner (Scripps) URL:http://oceans.mit.edu/event/sls-till-wagner-scripps X-ALT-DESC;FMTTYPE=text/html:\\n\\n\\n\\n\\nModeling iceberg drift and decay in modern and glacial climates\n\nUnder global warming\, the calving of icebergs into the polar oceans is expected to increase. As a result\, the role that icebergs play in Earth's climate system has recei ved a recent surge of interest\, and efforts are underway to explicitly re present icebergs in GCMs. A better understanding of how icebergs drift and decay will help facilitate an accurate representation of icebergs and gui de the interpretation of GCM results. In this talk I will present an ideal ized analytical model that we developed to aid this effort. I will use the model to address (i) which climate model variables are most important to accurately model iceberg evolution and (ii) whether climate models do a go od job simulating these variables. I then will turn to episodes of massive iceberg discharge\, called Heinrich Events\, which occurred during the la st glacial period. These events are believed to have had large-scale impac ts on the global climate system. However\, modeling icebergs that lived an d melted more than 10\,000 years ago comes with its own challenges\, as we will see. END:VEVENT END:VCALENDAR