Abstract
Abstract. The circulation and water mass properties in the Eurasian Basin are discussed based on a review of previous research and an examination of observations made in recent years within, or parallel to, DAMOCLES (Developing Arctic Modeling and Observational Capabilities for Long-term Environmental Studies). The discussion is strongly biased towards observations made from icebreakers and particularly from the cruise with R/V Polarstern 2007 during the International Polar Year (IPY). Focus is on the Barents Sea inflow branch and its mixing with the Fram Strait inflow branch. It is proposed that the Barents Sea branch contributes not just intermediate water but also most of the water to the Atlantic layer in the Amundsen Basin and also in the Makarov and Canada basins. Only occasionally would high temperature pulses originating from the Fram Strait branch penetrate along the Laptev Sea slope across the Gakkel Ridge into the Amundsen Basin. Interactions between the Barents Sea and the Fram Strait branches lead to formation of intrusive layers, in the Atlantic layer and in the intermediate waters. The intrusion characteristics found downstream, north of the Laptev Sea are similar to those observed in the northern Nansen Basin and over the Gakkel Ridge, suggesting a flow from the Laptev Sea towards Fram Strait. The formation mechanisms for the intrusions at the continental slope, or in the interior of the basins if they are reformed there, have not been identified. The temperature of the deep water of the Eurasian Basin has increased in the last 10 yr rather more than expected from geothermal heating. That geothermal heating does influence the deep water column was obvious from 2007 Polarstern observations made close to a hydrothermal vent in the Gakkel Ridge, where the temperature minimum usually found above the 600–800 m thick homogenous bottom layer was absent. However, heat entrained from the Atlantic water into descending, saline boundary plumes may also contribute to the warming of the deeper layers.
Highlights
The inflow of warm Atlantic water into the Makarov Basin observed in 1993 (Carmack et al, 1995) and the high temperatures found on the Arctic Ocean section in 1994 (Carmack et al, 1997; Swift et al, 1997) and on the Polarstern section in 1996 (Schauer et al, 2002b) at the Lomonosov Ridge indicate that Fram Strait branch water occasionally passes beyond the Gakkel Ridge, not just by mixing and heating the Barents Sea branch and as a distinct contribution, retaining some of its high temperature and salinity characteristics
Differential diffusion has been suggested as an important mechanism in these situations (Merryfield, 2002), but the time to establish the intrusions would be on the order of years (Merryfield, 2002; Kuzmina et al, 2011). This appears long considering the interleaving structures in the intermediate depth range encountered along the continental slope and in the eastern Nansen Basin (Figs. 7–9), and by the occurrence of intrusions almost immediately, when the Makarov Basin deep water passes through the intra-basin in the Lomonosov Ridge into the Amundsen Basin (Bjork et al, 2007)
The intrusions observed north of the Laptev Sea are similar to those found in the interior of the Nansen and Amundsen basins beyond the warm core of the Fram Strait branch
Summary
Recent studies of the Arctic Ocean circulation have focused on three discoveries, or rediscoveries, occurring in the 1980s and 1990s. (1) The realisation that the inflow of Atlantic water from the Norwegian Sea over the Barents Sea to the Arctic Ocean is of comparable magnitude as the inflow of Atlantic water taking place in Fram Strait (Rudels, 1987; Blindheim, 1989). (2) The shelf contribution to the formation of the halocline does not just involve the creation of dense water by brine rejection that eventually penetrates into the deep basin water column and the outflow of low salinity shelf water that overruns the winter mixed layer in the Nansen Basin, transforming it into a halocline water mass (Rudels et al, 1996). (3) The inflow of anomalously warm Atlantic water to the Arctic Ocean in the late 1980s and early 1990s (Quadfasel et al, 1991), and the relocation of the upper low salinity surface water from a large part of the Amundsen Basin into the Makarov Basin and even into the Canada Basin, and the shift of the surface front between the Atlantic and the Pacific derived waters from the Lomonosov Ridge to the Mendeleev. (3) The inflow of anomalously warm Atlantic water to the Arctic Ocean in the late 1980s and early 1990s (Quadfasel et al, 1991), and the relocation of the upper low salinity surface water from a large part of the Amundsen Basin into the Makarov Basin and even into the Canada Basin, and the shift of the surface front between the Atlantic and the Pacific derived waters from the Lomonosov Ridge to the Mendeleev. The present study reviews how these findings have guided recent research and in particular the oceanography work from icebreakers conducted within DAMOCLES (Developing Arctic Modeling and Observational Capabilities for Long-term Environmental Studies). It describes how observations made in the late part of the 2000s have improved our understanding of the Arctic Ocean processes and circulation
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