Dense Water Production in Storfjorden, Svalbard, From a 1-Year Time Series of Observations and a Simple Model: Are Polynyas in a Warming Arctic Exporting Heat to the Deep Ocean?

Abstract

The formation of dense Brine-enriched Shelf Water (BSW) in Storfjorden is analyzed during Winter 2016–2017 from mooring observations, a polynya model nudged to satellite observations, and an original BSW production model. The ice season was two months shorter than average, yet 44.2 ${\text{km}}^3$ of sea ice were formed, in line with estimates for the period preceding the atlantification of the Barents Sea in the mid-2000s: A thinner, more fragile ice may favor polynya openings and frazil ice production. A saline specimen of BSW was produced in large volumes, corresponding to an annual mean transport of 0.042 Sv, larger than previous estimates. The important production is due to the preconditioning of the polynya with a more saline source water, exceeding the pre-2005 values by 0.37. The BSW overflow was observed on the West Spitsbergen shelf slope from hydrographic sections down to 750 m, thus entering the Norwegian Sea Deep Water layer. Its core temperature was about $1°$C warmer than the pre-2005 values owing to the entrainment of a warmer water in Storfjordrenna, suggesting that a part of the excess surface heat of the Barents Sea could be exported into the deep ocean. Overall our results suggest that dense water formation in the Storfjorden polynya may not, at least for now, be hampered by the atlantification of the Barents Sea, and perhaps even temporarily favored by the more saline source water. Anomalous atmospheric warming during the Winter-Spring may however disrupt the production, as was observed 1 year before.