Water mass distribution and polar front structure in the western Barents Sea

Abstract

The water mass distribution in the western Barents Sea, the thermohaline structure of the western Barents Sea Polar Front, and the local formation of a dense water mass are described on the basis of an analysis of historical hydrographic data. This study concentrated on the frontal region between Bjørnøya and Hopen Island where Arctic water is found on the Spitsbergen Bank and Atlantic water in the Bear Island Trough and Hopen Trench. The distributions of Atlantic and Arctic waters in relation to topography were consistent with the hypothesis that the location of the polar front is fixed at about the 250 m isobath by the barotropic circulation of Atlantic water within the Bear Island Trough and Hopen Trench. In winter, vertical gradients of temperature and salinity were weak throughout the frontal region, consistent with a barotropic, topographically controlled front. In summer, vertical gradients remained weak below 100 m depth but increased in the upper layer as a result of the presence of fresh, warm surface water produced by melting ice. The topographic control of thermohaline properties at the surface was disrupted by the meltwater pool, and the meltwater contributed to water mass modification in the frontal region. The following seasonal cycle of water mass formation was hypothesized: Summer heating melts the sea ice on the Spitsbergen Bank and produces the surface meltwater pool. This meltwater not only increases vertical thermohaline gradients on the bank but also crosses the front and freshens the surface layer throughout the western Barents Sea. Subsequent winter cooling, which creates ice over the bank, also forms dense water in the Bear Island Trough and Hopen Trench by convective mixing of Atlantic water and the overlying meltwater.