September 12nd Daniel ENDERTON MIT-EAPS Studies of the total meridional heat transport and its atmospheric and oceanic partition
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ABSTRACT: The degree to which the total meridional heat transport and its partition is sensitive to the details of atmospheric and oceanic circulation is explored in models and data. A series of coupled GCM calculations is described in which idealized ocean basins impose geometrical constraints on ocean circulation. A wide range of ocean heat transports and heat transport partitions are found, but with more modest variations in the total meridional heat transport. The presence or absence of polar ice, and hence the global climate, is found to be sensitive to the ability of the ocean to carry heat to high polar latitudes. The results are diagnosed in the context of simple models and scalings which compare the strength of the atmospheric and oceanic circulations and the energy contrasts across the flows. Parallels are drawn with present and paleo climate.

September 17th John TAYLOR MIT-EAPS The Evolution of a Symmetrically Unstable Mixed Layer Front
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ABSTRACT: We have examined a symmetrically unstable density front using linear stability theory and numerical simulations. The initial horizontal density gradient is large enough to overcome the stabilizing influence of stratification and rotation to make the mixed layer potential vorticity (PV) negative and drive symmetric instability. A secondary Kelvin-Helmholtz (K-H) instability develops from the symmetric motions and rapidly fluxes PV into the mixed layer, thereby stabilizing the flow. While the physical parameters used in this study correspond to a front in the ocean mixed layer, many of the conclusions apply to symmetric instabilities in the atmosphere.

September 24th Robert PICKART WHOI How does Pacific water enter the interior Arctic Ocean ?
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ABSTRACT: The manner in which Pacific Water exits the Chukchi Sea and enters the interior Arctic Ocean is investigated using a combination of data and models. This includes how the flow is channeled through the two major canyons of the Chukchi Sea. It is argued that hydraulic processes are active in both canyons, significantly altering the structure and properties of the northward flow. The shelf-break jet that forms from the canyon outflows is elucidated using high-resolution mooring data and a simple numerical model. Particular focus is placed on the flow of winter Pacific water and how it might ventilate the basin interior.

October 1st Anne Willem OMTA Faculty of Earth and Life Sciences, Amsterdam, NL Critical turbulence revisted: The impact of submesoscale vertical mixing on phytoplankton patchiness
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ABSTRACT: This is purely theoretical (simulation) work, in which I have looked at phytoplankton distributions in a submesoscale baroclinically unstable eddy under different light conditions. It turns out that the plankton patterns are very different, if the plankton is light-limited than if the plankton is nutrient-limited which can be understood with a variant of Jef Huisman’s critical turbulence concept. Omta et al., J. Mar. Res. 66, 61-85 (2008)

October 8th Carl WUNSCH MIT-EAPS Altimetric spectra, trends, and low frequency ocean variability
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ABSTRACT: Evaluation of the significance of apparent long-term trends in the ocean circulation and sea level, as well as the testing of the skill of time-varying models, requires a description of the background variability. As a step toward that end, the longest available truly global records (15 years of satellite altimetry plus fragmentary other bits) are examined in an effort to generalize about oceanic behavior below one cycle/year.

October 15th John MARSHALL MIT-EAPS Using dynamics to interpret satellite altimetric observations, and vice-versa.
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ABSTRACT: In this talk I will use inferences from text-book dynamics (the theory of linear Rossby waves, baroclinic instability and geostrophic turbulence) to discuss two topics inspired by satellite observations, and the connection between them: (i) The interpretation of the propagation of surface altimetric observations in terms of linear planetary waves and geostrophic turbulence (ii) The geography of eddy stirring and mixing in the southern ocean: altimetric evidence for enhanced mixing at critical levels.

October 22nd Anthony KIRINCICH WHOI Calculating Reynolds stresses from ADCP measurements in the presence of surface gravity waves using the cospectra-fit method.
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October 24th (SPECIAL DATE !) Xavier PERROT LPO, Brest, FRANCE Vortex interaction in a non-uniform flow
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ABSTRACT: How do interact two same-signed vortices when they are embedded in a non-uniform flow? An analytical study, with a point-vortex modelisation, shows the existence of equilibrium, frequency modulation and chaotic motion. A comparison with a numerical model of extend vortices will be presented.

October 29th Sheekela BAKER MIT-EAPS On the Structure of Agulhas Eddies
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ABSTRACT: Eddy-eddy interactions within the upper and deep water column using observations and model simulations will be presented. Dipole dynamics provides a mechanism of enhanced eddy motion. Heton-like dipole motion aids in the shoreward and seaward propagation of Agulhas eddies and supplements the known tendencies of eddy motion. Such structures improve our understanding of Agulhas eddy trajectories, speeds, and interactions with the slope.

November 5th Peter DIAMESIS School of Civil and Environmental Engineering Cornell University Numerical Modeling of High Reynolds Number Stratified Wakes and Implications for Oceanic Turbulence
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ABSTRACT: The wakes of topographic features (islands, mountains, seamounds, headlands etc.) in the stably stratified ocean drive high vertical transport and diapycnal mixing in the near field and can establish distinct (sub)mesoscale eddy structures far from the source. Laboratory and numerical studies of the idealized model of the stratified wake of a towed sphere have provided critical insight on the interplay between shear-driven turbulence and stable stratification in a geophysical context. In this talk, results from highly parallel spectral multidomain direct numerical simulations (DNS) of stratified sphere wakes will be presented for a broad range of sphere-based Reynolds and Froude numbers.Distinct modifications in wake structure and dynamics are observed as the Reynolds number, Re is varied by a factor of twenty. The duration of the period of adjustment of three-dimensional turbulence into a quasi-two-dimensional buoyancy dominated flow is prolonged with increasing Reynolds number, Re. At Re=105, secondary Kelvin-Helmholtz instabilities and turbulence, driven by the vertical shear of the large-scale quasi-horizontal motions, are clearly observed for as late as Nt~100, where N is the stratification frequency. A -5/3 horizontal kinetic energy spectrum is obtained suggesting a horizontal Kolmogorov-like forward cascade at late times. In addition, significant vertical transport and mixing accompanies the secondary motions suggesting a mechanism for (sub)mesoscale-driven small-scale turbulence in the ocean. The above findings motivate the reconsideration of the commonly perceived life-cycle of a stratified turbulent event and the possible reinterpretation of recent oceanographic observations.

November 12nd Fanny MONTEIRO MIT-EAPS Diversity and habitat of nitrogen fixers in a global ocean model
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ABSTRACT: Nitrogen fixers, or diazotrophs, are important organisms in the nitrogen cycle of the ocean. They fix most of the nitrogen to the global ocean necessary for marine life. I explore the diazotroph diversity and the factors that control their habitat in a global ocean model. An ecosystem is stochastically generated with many tens of potentially viable phytoplankton from ranges of physiologies guided by laboratory and field observations. When placed in the model environment, the ecosystem self-assembles and the fittest phytoplankton survive. Analogs of the 3 major types of diazotrophs (Trichodesmium, unicellular cyanobacteria and diatom-diazotroph associations) are successful in the model. They occupy habitats consistent with those observed in the ocean, confined to tropical and subtropical waters. I use the model results and ecological theory to identify the trade-offs which control their habitat. Iron plays an important regulating role due to the high iron requirement of diazotrophs. In the model’s South Pacific, diazotroph abundance is extremely sensitive to the delivery of iron and parametrization of its biogeochemical cycle.

November 19th CANCELLED ! Neven-Stjepar FUCKAR AFFILIATION TBA
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ABSTRACT: TBA

November 26th Mick FOLLOWS MIT-EAPS The Organization of Marine Phytoplankton Communities
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ABSTRACT: We explore the relationship between marine phytoplankton community composition and their nutrient environment in a model of the global oceans. The model represents many tens of potentially viable phytoplankton species and explicit “survival of the fittest” organizes the ecosystem. We use this as a platform to examine the utility of resource competition theory, an established conceptual tool in ecology, to qualitatively and quantitatively describe a relatively complex marine ecosystem. We will also comment on the underlying foundations of marine ecosystem models

December 3rd Fei CHAI School of Marine Sciences, University of Maine TBA
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ABSTRACT: TBA

December 5th (SPECIAL DATE !) Tom ROSSBY Univ. of Rhode Island Some new results on water mass pathways and transformations in the Nordic Seas
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ABSTRACT: Recent Lagrangian studies of currents in the Nordic Seas show that topography plays a controlling role on circulation at all depths. In the past warm water flow north through the Nordic Seas was inferred to take place along two essentially separate pathways. Instead, the cooling of waters at high latitudes (in the Lofoten Basin) appears to force a barotropization of the inflow as evidenced by the striking cross-flow from the outer baroclinic to the inner barotropic branch of the Norwegian Atlantic Current system. The outflow through the Shetland Channel towards the NE Atlantic follows the bathymetry almost slavishly, but before the waters can exit through the Faroe Bank Channel considerable activity takes place, as if first having to reduce the ‘tallness’ or PV of the exiting waters. The first major step in water mass transformation (densification) takes place in the Lofoten Basin. We present some recent isopycnal water mass analyses illustrating where the transformations take place and the likely mechanisms involved. A striking consequence of the convective processes is the increasing spiciness of the densified waters. This signature appears to be a useful signature of where the transformations are taking place.

December 10th Manfredi MANIZZA MIT-EAPS Modeling the Carbon Cycle of a giant polar lake : the Arctic Ocean
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ABSTRACT: The top part of the Arctic Ocean is strongly influenced by an extraordinary amount of freshwater discharged by rivers along the entire basin (~10 % of the global freshwater depsite the Arctic is only 1 % of global ocean volume). This remarkable freshwater discharge is also associated with a large input of dissolved organic carbon (DOC, 35-40 Tera gC/year) that is produced by the surrounding terrestrial ecosystems. The abundance and spatial distribution of DOC in the Arctic Ocean is controlled by the interplay between the ocean circulation and mircobial degradation. Due to these two processes, salinity and DOC load become then distinct signatures of water masses of different origin (coastal vs off-shore) and their relationship strongly depends on the rate of DOC microbial degradation superimposed to surface ocean circulation.By combining both numerical tools and theoretical models I will show : (1) how and why I can realistically model the DOC-Saliniy relationship matching field data and (2) how important is the riverine DOC input (due to its conversion into inorganic carbon) for the air-sea fluxes of CO2 at basin scale. In the same context, I will also provide a general outlook on the recent and evident trend of Arctic sea-ice loss and its implications for the ocean CO2 sink of this region.