St.Lawrence Island Polynya: A factory for ice and dense water

Knut Aagaard (UW), Thomas Weingartner (UAF), Detlef
Quadfasel (University of Copenhagen), Jens Meincke (University of Hamburg),
Seelye Martin (UW), Richard Moritz (UW)

Corresponding author: Knut Aagaard (aagaard@apl.washington.edu)

OVERVIEW

We are in the analysis phase of a field study to test new theoretical ideas about shelf convection and the spreading of ventilated waters away from the convecting region.  These ideas, which are based on baroclinic instability of the front bordering such a region, have direct applicability both to open ocean convection and to that on the shelf, e.g., with respect to the equilibrium that is established between the export of excess density via the eddy fluxes across the boundary of the convecting region and the import of excess density across the sea surface from the buoyancy loss to the atmosphere.  In both cases this equilibrium limits the oceanic density anomaly that can be generated.  Our focus is on whether:
- The salinity of the dense water formed in the convecting region during the geostrophic adjustment phase increases linearly with time and with the magnitude of the surface flux forcing;

- The density anomaly scale and the equilibration time scale are consistent with the Chapman and Gawarkiewicz [1997a] formulation;

- A front forms on the offshore boundary of the convecting region, with the along-front flow tending toward geostrophic balance;

- Frontal instabilities develop;

- These instabilities lead to a cross-shelf eddy salt flux equal to the salt rejection rate predicted from a surface heat balance model for the region of active convection;

- The instabilities shed vertically stratified eddies with cyclonic flow at the surface and anticyclonic flow at the bottom;

- The eddies migrate across isobaths; and

- We can quantify the salinity changes experienced by a parcel of dense water as it propagates offshore along the anticipated eddy trajectory.

For published results, see:  Drucker, R., S. Martin, and R. Moritz (2003), Observations of ice thickness and frazil ice in the St. Lawrence Island polynya from satellite imagery, upward looking sonar, and salinity/temperature moorings, J. Geophys. Res., 108, 3149, doi:10.1029/2001JC001213, C5.

PRIOR REFEREED PUBLICATIONS

Schumacher, J.D., K. Aagaard, C.H. Pease, and R.B. Tripp, Effects of a shelf
  polynya on flow and water properties in the northern Bering Sea, J.
  Geophys. Res., 88, 2723-2732, 1983.

We gratefully acknowledge financial support for this work from the National Science Foundation (NSF).

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