Nordic and Barents Seas Cooling – Where Does the Heat Go?

Lars Henrik Smedsrud1, Oeystein Skagseth2, Ailin Brakstad3, Tor Eldevik4, Morven Muilwijk4 and Marius Årthun4, (1)University of Bergen, Geophysical Institute, Bergen, Norway, (2)Insititute for Marine Research, and Bjerknes Centre for Climate Research, Bergen, Norway, (3)Bjerknes Centre for Climate Research, University of Bergen, Geophysical Institute, Bergen, Norway, (4)Geophysical Institute, University of Bergen and Bjerknes Centre for Climate Research, Bergen, Norway
Abstract:
The Nordic Seas receives a large inflow of warm Atlantic Water (AW) across the Greenland Scotland Ridge (GSR), representative values is about 8 Sv and +8°C. This AW heat plays a crucial role in regulating regional climate, modifying Atlantic sector sea ice cover, and may directly contribute to ocean driven melting along the North-East coast of Greenland. When the waters return southwards as cooled water, most of it quite dense, the temperature is around -1°C – documenting a total Arctic, Nordic and Barents Seas cooling of over 500 TW. Both the AW inflow itself and the onwards destiny of this heat has varied spatially and over time. Within the Nordic and Barents Seas the three main heat sinks are 1) the atmosphere, 2) The Arctic Basin, and 3) sea ice and glacial melting.

The Barents Sea heat loss (~75 TW) is a dominant heat source for the Arctic atmosphere and here there has been a direct conversion of AW into dense water contributing ~30% of the GSR overflow. Until 2010 this Barents Sea “cooling machine” – warmer Atlantic inflow, less sea ice, more regional ocean heat loss – operated steadily – but this has now changed. Most of the Barents Sea is now open AW and any additional heat loss from more open water is relatively marginal.

Utilizing coupled climate model simulations, ocean re-analysis and more than 100 years of observations, the ocean heat transport and heat loss variability over the Nordic and Barents Seas will be evaluated, based on current-state of the art understanding of heat loss, dense water formation, sea ice loss and melting of marine-terminating glaciers. Initial results show large decadal-scale variability of the AW inflow dictated by the Atmospheric forcing, but also that there is a significant warming over the recent decades along the entire AW Nordic Seas inflow path. This recent warming is larger than the warm period in the 1920’s and 1930’s – and appears most strongly in the Barents Sea that today dominates both the variability and mean ocean heat transport towards the ocean beneath the Arctic sea ice. The portion of the AW heat that re-circulates in Fram Strait and is available for melting the exported Arctic sea ice and Greenland glaciers has likely also increased, but what drives changes in this re-circulation is under present investigation.