Formation and Transport of Cold Saline Water on the Laptev Sea Shelf

It is believed that brine enriched water, which is produced on shelves in winter attains sufficient density to cascade down continental slope ventilating various water layers of the Arctic Ocean. Despite the fact that the general concept of this process was formulated by F. Nansen a century ago, our present knowledge about Arctic cascades is based on theoretical speculations and numerical modeling rather than on direct observations of dense water forming and cascading at specific locations in the Arctic Ocean. In the present study our intention was to recreate the process of dense water formation and cascading in a specific area of the Arctic Ocean by filling a gap between two seasonal hydrographic surveys using numerical model output. We applied a primitive-equation model forced by constant surface buoyancy flux to simulate a dense water outflow from the shelf through the winter of 1984-85 when the northwestern Laptev Sea was covered by recurrent hydrographic surveys. Using meteorological, hydrographic and sea ice data we formulated hypotheses for our numerical model. The model results were then checked against available hydrographic observations, theoretical predictions, and the output of other, comparable numerical models. Our analysis has shown that between October and April, 1985 Laptev Sea shelf waters had received an amount of salt almost 5 times greater than the amount that accumulated. This excessive salt was transported off the shelf by dense water flow (cascading) through the bottom boundary layer with an average thickness of about 40 m. This dense water would have reached at least 1000 m depth, but strong stratification prevented it from penetrating deeper than 400 m down slope. According to model results, the cold halocline layer acts as a sink for salt entering from the shelf (at depths less than 200 m), and from the Atlantic Water layer (at depths larger than 200 m). The later is the result of compensatory upwelling, which carries warm and salty water upslope.