BARENTS SEA WATER INPUT T0 THE EURASIAN BASIN AND ITS VARIABILITY
U. Schauer1, B. Rudels2, E. Fahrbach1, H. Loeng3
l) Alfred-Wegener-Institut fuer Polar- und Meeresforschung, D-27515 Bremerhaven, Germany
2) Finnish Institute of Marine Research, FIN-00931 Helsinki, Finland
3) Institute of Marine Research, N- 5024 Bergen-Nordnes, Norway
Introduction
For the ventilation of the Arctic Ocean, the Barents Sea plays a special role since l) it is the deepest Arctic shelf sea (>300 m), 2) it receives the most saline inflow as compared to other shelf seas, and 3) it has a permanent inflow and therefore supplies permanently water to the central basins (Rudels, 1987; Rudels et al., 1994). In addition, like on other shelf seas, there is a saisonal generation of dense cold brine enriched waters as a consequence of ice formation which was proposed by Nansen (1906) to be a mechanism to ventilate the deep Arctic basins.
Atlantic Water enters the western Barents Sea as a part of the large scale circulation of the Norwegian/ Greenland Sea. In addition, the Norwegian Coastal Current, continuously supplied with continental fresh water, follows the coastline and provides low salinity water to the Barents Sea. Both currents continue eastward into the central Barents Sea, with a combined transport of 1.9 Sv (106 m3/s) (Blindheim, 1989). Since the St. Anna Trough has a deep connection to the eastern Barents Sea, it was assumed that this water leaves the shelf through the St. Anna Trough after modification through cooling, freezing/melting and mixing.
Using hydrographic observations from “Johan Hjort”, “Dalnye Zelintsy” and “Polarstern” in 1991 and 1996 in the Barents and northern Kara Sea and time series from moored instruments in the western (Schauer, 1995) and eastern Barents Sea (Loeng et al., 1993), we trace the modification of the water masses and the flow from the passage between Novaya Zemlya and Franz-Josef-Land to the St. Anna Trough.
Flow between the eastern Barents Sea and the St.Anna Trough
Two sections from different years, one across the St. Anna Trough (“P1996”, Fig.l) and one across the eastern Barents Sea (“J1991”), reveal continuous flow between the two areas. In both sections, warm water is present 0n the western/northern side while the eastern/southern slope is dominated by temperatures below 0℃. The warm core, located at 200 m in the western St. Anna Trough, is a continuation of the Atlantic layer advected from Fram Strait in the boundary current along the continental slope (Hanzlick and Aagaard, 1980). Current measurements show that also the water in the warm core south of Franz Josef Land flows southwestward. This constitutes an anticycIonic flow of Fram Strait derived Atlantic Water through the St. Anna Trough into the central Barents Sea.
The layer of cold, low salinity water attached to the eastern/southern slope bottom is also found in both areas. It extends in a 150 m thick layer from the upper edge to the central deep channels. The density distribution is consistent with a highly sheared flow. Current measurements north of Novaya Zemlya (J2) show eastward flow over the entire water column, with the speed in the lower layer almost twice as high as in the upper layer (Fig. 3). Loeng et al. (1993) computed a total eastward transport of 1.9 Sv.
In the eastern St. Anna Trough, the northward baroclinic component of the geostrophic velocity increases towards the bottom and an extreme vertical shear is present in the easternmost part. Relative to the surface, the water below 50 m flows northward with velocities between up to 0.25 m/s. The interpretation of the profile as bottom-intensified, northward flow is consistent with shipborne ADCP measurements of the velocity profile, which agree in range and form with the geostrophic profile. Given a mean northward speed of 0.2 m/s for the 150 m thick layer of cold water at the bottom of the eastern 100 km of the St. Anna Trough, the total inflow of cold, low salinity water to the Nansen Basin would be 3 Sv, slightly more than the mean flow in the eastern Barents Sea.
