A Model Study of Circulation and Biogeochemical Processes on the West Antarctic Peninsula

John M. Klinck, Michael S. Dinniman, and Eileen E. Hofmann

Circumpolar Deep Water (CDW) is a relatively warm, salty and nutrient rich water mass which flows across the shelf break of the west Antarctic Peninsula. This water mass moderates the ice cover through heat flux, provides a relatively warm subsurface environment for some animals and provides nutrients to stimulate primary production. CDW exchange is known to be episodic, but persistent, and is thought to occur at specific locations due to bottom topography. A circulation study using an eddy permitting 3D numerical circulation model analyzes the exchange of CDW. Macro-nutrients and estimated biological uptake processes are included to analyze nutrient pathways and selection processes that result in diatoms or algae blooms.

We use the Rutgers/UCLA Regional Ocean Model System (ROMS) with a grid resolution of 5 km horizontally and 24 levels vertically. A gridded bathymetry is derived from the Smith and Sandwell bathymetry with modifications around Marguerite Bay from digitized nautical charts (Beardsley). Initial temperature, salinity, nitrate and silicate are derived from the World Ocean Atlas (WOA98). Monthly climatological ECMWF reanalysis wind stress is applied to the top three layers of the model. Ice concentrations are specified using the SSM/I climatology. The COARE bulk flux algorithms are used to compute the model surface heat and salt fluxes, as modified by the sea ice. Vertical mixing in the interior and surface boundary layer uses the K profile parameter (KPP) scheme (modified for the presence of ice). An annual climatology of depth averaged volume transport was estimated from the Orsi et al. (1995) frontal locations. A radiation boundary condition with adaptive nudging (Marchesiello, 2000) to monthly climatologies of the tracers and the estimated volume transport is used on open boundaries.

The model circulation compares favorably to general schematics of the flow. The Antarctic Circumpolar Current (ACC) flows along the shelf break, although the model has stronger and less variable circulation than is shown by recent ADCP measurements. A weak, southward coastal flow, which turns into Marguerite Bay and flows cyclonically around the bay, matches the general pattern of recent ADCP measurements (Muench and Padman). Subpycnocline temperature shows evidence of intrusion of warm water from the ACC onto the shelf.