THE SIBERIAN COASTAL CURRENT: A WIND AND BUOYANCY-FORCED ARCTIC COASTAL CURRENT
Thomas J. Weingartner*
Institute of Marine Science, University of Alaska, Fairbanks, Alaska
Yasunori Sasaki
Japan Marine Science and Technology Center, 2-15, Natsushima, Yokosuka 237
Vladimir Pavlov
Arctic and Antarctic Research Institute, St. Petersburg, Russia
1. INTRODUCTION
The huge river runoff (nearly 10% of the global river discharge) into the Arctic Ocean profoundly affects the hydrography and circulation of the ocean interior (Aagaard and Carmack, 1989). That influence occurs via direct contributions to the mixed layer and through mediation of the modal salinity properties of the dense winter shelf water that ventilates the subsurface layers of the Arctic Ocean (Meilling, 1993). Arctic continental shelves play an important role in transporting and modifying this freshwater, but there are relatively few studies of these shelf processes.
Here we describe dispersal and mixing mechanisms within the Siberian Coastal Current (SCC) in the western Chukchi Sea using shipboard measurements of ocean velocity, temperature, and salinity obtained in the fall of the years between 1992 and 1995.
The SCC apparently originates with an eastward flow of Laptev Sea water (diluted by the Lena River discharge) through the straits of the New Siberian Islands and into the East Siberian Sea.
The SCC continues eastward across this shelf and incorporates the discharges from the Indigirka and Kolyma rivers. It then enters the western Chukchi Sea through Long Strait and terminates on this shelf (Coachman et al., 1975). In addition to the buoyancy forcing provided by the discharge, winds play an important role in the circulation of these shallow shelves (Weingartner et al, 1998). Both forcing functions vary substantially throughout the year, implying similarly large seasonal variations in the hydrographic structure and dynamics of the SCC. Our measurements were made in September and October which is a transition season for forcing on arctic shelves. At this time the standing stock of freshwater on the shelf is a maximum, but river discharge is rapidly decreasing from its peak, mid-summer rates. On the other hand, winds are mild in summer, but the strength and intensity of storm winds increases in autumn.
2. RESULTS
Figure 1 shows temperature and salinity contoured as a function of depth and crossshore distance in the western Chukchi Sea from October 1993 (left panel) and September 1995 (right panel), The outermost portion (>150 km) of the 1993 transect was vertically homogeneous and consisted of relatively warm (>2℃), saline (>32.0) Bering Sea Water (Coachman et al, 1975). A broad (〜75 km wide) front separated this water mass from the cold (<1.0℃), dilute (<30.0) coastal waters comprising the SCC. Waters inshore of the 30m isobath were weakly stratified whereas offshore of this isobaths a strong halocline (which eventually bends upward to form the front) separates SCC water from Bering Sea Water. ADCP data showed that, offshore of the front, the flow was southeastward due to northwesterly winds. Shoreward of, and within the front, the thermohaline structure implied a southeastward alongshore baroclinic, geostrophic flow. However, the observed alongshore velocities were northwestward and swift (25 cm s-1). This flow was neither tidal (tides are <5 cm s-1) or wind-driven as the winds were calm along the coast. Satellite thermal infrared imagery showed that the coastal region was replete with meanders, dipole eddies and “squirt-like”features. These features are reflected in Figure 2 which shows ADCP velocities and surface temperatures and salinities from a 400km long
*Corresponding author address;Thomas J. Weingartner, Institute of Marine Science, University of Alaska, Fairbanks, AK 99775-7220; e-mail:weingart@ims.alaska.edu
