Impact of eastern Arctic shelf waters on the Nansen Basin intermediate layers

Abstract

The Eurasian shelves supply water to the Nansen Basin intermediate layers in two ways: as buoyancy‐driven plumes of dense winter water and as permanent inflow of the Barents Sea branch of Atlantic Water. While the plumes are local and seasonal phenomena, the Barents Sea flow is part of the large‐scale circulation. Both interact with Atlantic Water, which enters the Arctic Ocean through Fram Strait and moves as a subsurface boundary current eastward along the continental slope. During the Polarstern cruise ARK IX/4 in summer 1993, the Fram Strait branch was observed as a narrow core within tens of kilometers of the Barents Sea shelf edge. Here, several patches of cold, low‐salinity water spread across the slope down to about 500 m depth. Their origin is assumed to be the northern Barents Sea. They mix with the warm, saline Fram Strait branch water (FSBW), so that the core properties of the latter become modified downstream. In the eastern Nansen Basin the Fram Strait branch is displaced toward the inner basin by inflow of the Barents Sea Branch of Atlantic Water (BSBW). This inflow appears as a broad (200 km) wedge extending from 200 to 1300 m depth. BSBW is colder and less saline than water of the Fram Strait branch, and it is less dense and less stratified than the ambient water. Both branches appear to undergo vigorous mixing while spreading eastward, so that any eastward continuation of the boundary flow transports about 50% BSBW and 50% FSBW above 600 m and about 80% BSBW and 20% FSBW below that level toward the Canadian Basin. According to available observations, the Barents and Kara Seas are the only source areas for shelf waters ventilating the Nansen Basin below the halocline, and these waters constitute a freshwater input rather than a salt input. Winter shelf water from the Laptev Sea cannot contribute to layers deeper than the upper halocline.