The role of quasi-stationary flaw polynya in formation of dense shelf waters in the wintertime and their subsequent slope cascading (the Laptev Sea case study)

Abstract

Shelf areas in the region of the Severnaya Zemlya Archipelago in the Laptev Sea are characterized by existing quasi-stationary flaw polynya that periodically opens throughout the entire wintertime under the action of strong offshore winds, which occur during the passage of cyclones. In periods of the open water surface, a near-surface turbulent layer or forced convection layer is formed in the flaw polynya; the water in the layer formed undergoes intense salinization and its dense increases due to active volumetric frazil ice production. As a result of the gravity force action, intense three-dimensional convective circulation develops in the underlying layers. It leads to a fast convective adjustment of the entire water column, especially, in the late winter, when residual stratification in the area of polynya is weakened with the total action of salinization due to the background static ΣMsback and periodical local frazil ice formation ΣMsf. On the whole for the entire winter period ΣMsf is 3.4 times greater than ΣMsback, although, during one month, probable lifetime of polynya with open water surface is several days. However, in these periods, salt fluxes with frazil ice production exceed background salt fluxes in the congelation polynya and background salt fluxes under heavy ice (limiting the polynya) 10–80 times. Spreading outside the polynia, dense shelf waters form in the area of polynya mesoscale baroclinic circulation, first generating intense shelf cascading, then intense slope cascading, which is of a local and random character. Some estimates of elements of baroclinic circulation of a convective origin in the area of polynia were obtained from the laboratory modeling results and are confirmed by field observation data.