AnSlope: Cross-Slope Exchanges at the Antarctic Slope Front

Project Description
AnSlope seeks an answer to the question: What is the role of the Antarctic
Slope Front and continental slope morphology in the exchanges of mass, heat,
and freshwater between the shelf and oceanic regimes, in particular those
leading to outflows of dense water into intermediate and deep layers of the
adjacent deep basins and world ocean circulation?

The importance to the global ocean circulation and climate of cold water masses
originating in the Antarctic is now understood, but the processes by which
these water masses enter the deep ocean circulation are not. We have developed
a program called AnSlope to address this problem. Our primary goal is to
identify the principal physical processes that govern the transfer of
shelf-modified dense water into intermediate and deep layers of the adjacent
deep ocean. At the same time, we seek to understand the compensatory poleward
flow of waters from the oceanic regime. We identify the upper continental slope
as the critical gateway for the exchange of shelf and deep ocean waters. Here
the topography, velocity and density fields associated with the nearly
ubiquitous Antarctic Slope Front (ASF) must strongly influence the advective
and turbulent transfer of water properties between the shelf and oceanic
regimes.

AnSlope has four specific objectives: [A] Determine the ASF mean structure and
the principal scales of variability (spatial from ~1 km to ~100 km, and
temporal from tidal to seasonal), and estimate the role of the Front on
cross-slope exchanges and mixing of adjacent water masses; [B] Determine the
influence of slope topography (canyons, proximity to a continental boundary,
isobath divergence/convergence) on frontal location and outflow of dense Shelf
Water; [C] Establish the role of frontal instabilities, benthic boundary layer
transports, tides and other oscillatory processes on cross-slope advection and
fluxes; and [D] Assess the effect of diapycnal mixing (shear-driven and
double-diffusive), lateral mixing identified through intrusions, and
nonlinearities in the equation of state (thermobaricity and cabbeling) on the
rate of descent and fate of outflowing, near-freezing Shelf Water.

AnSlope addresses these objectives with an integrated observational and
modeling program structured as follows. A collaborative core program begins in
2002, containing the components considered central to meeting AnSlope
objectives, primarily through acquisition of a set of measurements focused over
the outer continental shelf and upper slope of the northwestern Ross Sea. This
will allow us to assess the regional AABW production rate, and to identify the
cross-front exchange processes that must be taken into account when assessing
provision of dense water to the deep basins elsewhere around Antarctica. The
core elements are: moorings; CTD/LADCP and CTD-based microstructure; tracers;
and basic tidal modeling. "Enhancement" proposals, to be submitted separately,
request support for the modeling studies that are necessary to fully exploit
the measurements and develop the techniques for parameterizing cross-front
exchanges in regional and global models. Three cruises are proposed, beginning
in Austral summer 2003, over a period of 12 to 14 months. Moorings would be in
place throughout this period. The Italian CLIMA program in the Ross Sea
provides a valuable international enhancement for the AnSlope observational
component. The German BRIOS-2 coupled ice-ocean GCM program is complementary to
the US process-oriented modeling studies, and provides a test-bed for
AnSlope-generated parameterizations of cross-front exchange.

Additional information can be found at
http://www.ldeo.columbia.edu/res/div/ocp/projects/anslope.shtml