Brine formation through ice production in Storfjorden, Svalbard, estimated by
ERS-2 SAR imagery and simple ice drift and ice formation models

Abstract
The main goal of the Storfjorden study was to estimate the brine formation that results from salt rejection during sea ice production, by coupling ERS-2 SAR observations with simples ice drift and ice production models and in situ measurements. The water masses, their transformation and currents, especially regarding the salinity increase inducing a local thermohaline circulation, have been described from hydrographic measurements taken before and after the winter. The ice cover observations during the winter 1997/1998 showed the evolution of a large area of fast ice in the shallow area north of 78° N, and of persistent latent heat polynyas that develop under northerly winds between the fast ice and the sill of the fjord at 77° N. The SAR images were manually segmented into fast ice, polynia and pack ice. The polynya estimates were then interpolated with a simple ice drift model and we separated inside between open water and thin ice assuming frazil ice accumulation at the lee side of the polynya, where it consolidates in a thin ice cover. Using algorithms of frazil ice production in the open water area and ice growth under thin ice and fast and pack ice, a total ice production of 40 km3 was calculated. About two thirds of the total ice was formed inside the polynya that covered on average only 15% of the total area. This ice production released 1 Gt of salt that was rejected as brine to the underlying water column and could enrich the salinity of 4-5 times the Storfjorden volume by 0.3 PSU. Comparison with the ice production during the milder winter 1998/1999, where the vast fast ice cover in the north was absent, showed that a larger polynya situated over shallower waters could partly balance the lack of cold temperature regarding the brine formation and even produce more saline brine-enriched bottom waters.

Key words: Arctic Ocean, Svalbard, Storfjorden, sea ice, brine, polynyas, remote sensing, ERS-2 SAR