Synoptic Antarctic Shelf-Slope Interactions Study

Project Description
Short Title: SASSI
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Short synoptic transects will be undertaken circumpolarly and will radiate outwards across the Antarctic continental shelf and slope. Transects will incorporate insofar as possible:* Closely-spaced full depth CTD/ADCP stations plus profiles of PAR irradiance, bio-optical properties and fluorescence (EoI 9, 57, 310, 573, 585, 596, 635, 911).* Collection throughout the water column at stations of water samples for tracer, chemical and biological analyses including oxygen isotopes, carbon parameters, inorganic and organic nutrients and trace gases, and for biomass on deck incubation experiments to evaluate auto and heterotrophic activities (EoI 9, 573, 585, 596, 635, 911).* Deployment of moored instruments along each transect to measure temperature, salinity, current velocities, sedimentary fluxes and sea level for at least one year (EoI 9, 57, 310, 573, 585, 596, 635).* Deployment on the shelf of autonomous water samplers to collect weekly samples for tracer analyses (EoI 9).* Deployment of ice-hardened surface ocean drifters across the coastal and slope break current systems, measuring temperature, salinity, sea level pressure and location (EoI 9, 310, 573).* Air-sea heat and freshwater flux and meteorological measurements (EoI 9, 573, 585).* Swath bathymetric surveys of the complex shelf and slope terrain, both to assess local circulation and mixing processes, and to detect geological/glaciological phenomena such as iceberg scour (EoI 9, 237, 310, 573, 596).* Sedimentological observations including coring and biostratigraphy (EoI 596, 635)* Turbulent mixing measurements (EoI 9, 310, 573).* Continuation of hydrographic sections poleward beneath ice shelves and/or sea ice using autonomous underwater vehicles (AUVs) such as Autosub (EoI 9) and hot-water drilled access holes (EoI 310).* Use of AUVs to measure sea ice thickness distribution on the Antarctic shelf and slope (EoI 57)* Use of autonomous underwater vehicles and/or instrumented pelagic marine mammals to penetrate beneath sea ice and ice shelves to measure hydrographic and dynamical properties (EoI 9, 585), marine geological, chemical and biological characteristics (EoI 237)Additionally:* We will deploy subsurface Lagrangian floats to be tracked acoustically beneath the seasonal sea ice throughout the winter (EoI 9, 485, 573, 596). These will provide profiles of temperature and salinity, and geographical location, every 10 days. Plans are already in hand to ensonify the Weddell Sea, the offshore region of the Wilkes-Adelie Land and the western margin of the Antarctic Peninsula, to enable use of such floats. Extension of this tracking network to other regions surrounding Antarctica will be undertaken through SASSI to provide polar coverage to the global Argo programme.* Visible, passive microwave and synthetic aperture radar remote sensing (EoI 57, 585, 911) will be used to assess the seasonal/interannual variability of circumpolar coastal polynyas and of phytoplankton biomass. SAR, passive microwave and Cryosat altimetry will allow large scale monitoring of sea ice.* Numerical models will be developed to quantitatively study heat & freshwater fluxes and water mass transformations, and impacts of large iceberg calving events (EoI 57), processes of exchange between ice shelves and the open ocean (EoI 232), tides (EoI 573), biogeochemical cycling of C, N and P (EoI 635), short-term mesoscale instabilities, mixing processes and mass transports associated with gravity plumes across sloping bathymetry (EoI 596). Coupled ice-ocean models (EoI 585) will be analysed, and will assist in developing parameterisation for climate models.* Hot-water drilling through floating ice shelves (EoI 232, 310) will allow sub-ice-shelf CTD profiling and mooring deployment, together with acoustic determinations of basal melt rate.