Aspects of the Hydrography and Circulation of the Siberian Coastal Current
Thomas Weingarther
Institute of Marine Science, University of Alaska, Fairbanks, AK 99775
Tel: 1-907474-7993
Fax: 1-907-474-7204
weingart@jarvis.ims.uaf.edu
Yasunori Sasaki
Japan Marine Science and Technology Center, Yokosuka, Japan
Vladimir Pavlov
Arctic and Antarctic Research Institute, St. Petersburg, Russia
The thermohaline structure of the Arctic Ocean is profoundly influenced by the enormous river discharges from the surrounding continents. However, prior to entering the ocean interior this discharge is substantially modified by a variety of shelf processes. These water mass modification processes are highly non-linear because they depend upon the shelf stratification and circulation, which are, of course, linked to the freshwater discharge. Moreover, these processes are very time-dependent because of the acutely seasonal nature of the river discharge, wind-forcing, and shelf ice cover.
We explore these issues using several years of shipboard hydrography and acoustic Doppler current profiler (ADCP) data from the Siberian Coastal Current (SCC) within the western Chuckchi Sea. The SCC nominally flows across the entire length of the East Siberian Sea and eaters the western end of the Chukchi Sea along the Siberian coast. It transports river water from the Laptev Sea as well as the Indigirka and Kolyma rivers that empty into the East Siberian Sea. In some years the SCC is a prominent feature of the Chukchi shelf manifesting itself as a buoyancy-forced coastal current. However, in other years it is completely absent. These year-to-year differences are related to the mixing history of river and ambient shelf water. They also involve mixing processes at the river mouth that establish the subsequent transport pathway for the freshwater into the Arctic Ocean.
When present in the Chukchi Sea, the SCC appears to be very unstable because it is populated by numerous eddies and energetic squirts. The instabilities are very effective horizontal (and vertical) transport mechanisms that carry river water far offshore and mix it with ambient shelf water along the way. Indeed we find that the energy released by the conversion of available potential energy into eddy energy is an order of magnitude greater than the energy available for mixing by the wind field. Clearly, one effect of the instabilities is to weaken the SCC. However, they might also allow the development of a more persistent coastal flow because they enhance vertical mixing which could allow for the formation of a surface-bottom front. Coastal currents characterized by such fronts have a tendency to persist over vast alongshore distances.
