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Circulation and Water Mass Transformation in a model of the Chukchi Sea
Ventilation of the Arctic Halocline by Shelfbreak Eddies
The circulation and water mass transformation in a regional ocean-ice model of the Chukchi
Sea are discussed. The model has horizontal resolution
of O( 4 km), is forced by fluxes derived from daily NCEP reanalysis
fields, and has seasonally varying transport, temperature, and salinity
imposed at Bering Strait. Many of the observed characteristics of the mean circulation
and seasonal cycle in the Chukchi Sea are reproduced. The
discussion focusses on: the branching of the inflow transport into pathways
following Herald Canyon, Central Channel, and the Alaskan coast;
the pattern of ice melt; and the water mass transformation and formation of
winter water and hypersaline water. The ice melt pattern and timing is
strongly influenced by advection through Bering Strait. High frequency
forcing results in a larger region of ice melt, particularly over
the shoals and in the northern Chukchi Sea, compared to monthly mean
forcing. In the model, the seasonal cycle of salinity in the southern and central Chukchi
Sea is dominated by advection through Bering Strait, while local atmospheric forcing
and brine rejection are more important north of Herald and Hanna Shoals
and in Barrow Canyon. However, since the residence time in the Chukchi Sea
is generally less than 1 year, interannual variability in the Bering Strait
salinity will be reflected in the salinity across the Chukchi Sea and at
Barrow Canyon.
The Arctic halocline is a layer of cold, fresh water in the upper
200 m that overlies the deeper warm, salty waters of Atlantic Ocean
origin. The maintenance of this halocline is not well understood, but is
crucial for the ice cover in the Arctic, and for the basin-scale balances
of heat and salt. Observations indicate that the halocline in the interior
of the Beaufort Sea is populated with very small anticyclonic eddies
composed of cold, fresh waters that originated on the shelf. It is
speculated that these eddies are important for the maintenance of the
halocline and also transport tracers and nutrients from the shelf region
into the basin interior. In this project, an idealized, high resolution
ocean general circulation model is used to study this eddy formation process
and its possible role in the maintenance of the Arctic halocline. The model
results are being compared to and evaluated against observations collected
by Dr. R. Pickart (WHOI) along a high resolution mooring array just east of
Barrow Canyon during 2002-2004 as part of the Shelf Basin Interaction Program.
The results indicate that cold fresh waters flow from the Chukchi Sea along
the shelf-break in a narrow boundary current and that this boundary
current is strongly unstable and able to form numerous small-scale
anticyclonic eddies, in general agreement with observations.
This work has been generously supported through grants from the
National Science Foundation Office of Polar Programs.
Recent manuscripts on these subjects :
Spall, M. A., 2007. Circulation and Water Mass Transformation in a Model of
the Chukchi Sea. J. Geophys. Res. ., 112, C05025,doi:10.1029/2005JC002264
Spall, M. A., R. S. Pickart, P. Fratantoni, A. Plueddemann, 2007. Western Arctic
Shelfbreak Eddies: Formation and Transport. submitted: Journal of Physical
Oceanography .
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