Abstract

Newly available historical Russian data are used to quantify year-to-year variations in the structure and properties of the halocline and Atlantic Water layers in the eastern Nansen Basin. The data come from a series of aerial surveys of the central Arctic Ocean done during winter between 1973 and 1979, and repeated "Polygon" surveys of the shelf, slope, and basin north of Severnaya Zemlya in the 1980s, and thus allow a perspective on shelf-basin exchange. A water-mass census shows substantial survey-to-survey variability in several water-mass categories, with volumetric fluctuations of ∼17% in the Upper Polar Deep Water category, ∼14% in Atlantic Water, and ∼39% for cold surface waters with T < −1.5°C. Mean water-mass production rates in the polygon area are found to be 0.6–1.2 Sv for Upper Polar Deep Water, and an effective loss rate of 0.75–1.5 Sv is found for Atlantic Waters. On average Atlantic Water loses 16% of its initial heat content within the 350 km-long survey area, possibly enhanced by double-diffusive processes. Mean upward heat fluxes above the Atlantic Water are estimated to be between 4 and 6 W/m2, based on heat budget considerations. Upward heat fluxes of this magnitude would have a major effect on sea ice, which is regularly observed to be thinner in this area of the Nansen Basin. Shallow-water profiles taken close to Severnaya Zemlya show cold and salty waters denser than offshore waters at similar depths, and evidence of convection is seen in many profiles taken over the continental shelf and slope, reflecting deep convective events extending in some cases below the deepest observed depth of 1000 m.

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