The recent – and expected future – decline in Arctic sea ice cover has become an icon of climate change. As parts of the ice cover are replaced by open waters, more heat can be released directly from the ocean to the atmosphere above, and thus temperate the regional climate. As opposed to the central Arctic Ocean where a cold halocline insulates the surface ocean from the warmer waters below, net ocean heat is directly available for the atmosphere in the shelf regions where temperate waters from the Nordic Seas meet the ice edge.
Heat and salt are transported into the Arctic by the West Spitsbergen Current (WSC), which flows northward along the western coast of Svalbard and then turns eastward into the Arctic. Along its way the WSC looses large amounts of heat due to heat loss to the atmosphere, melting of sea ice and mixing with other water masses. This loss of heat has previously been determined by observing the decreasing temperature of the WSC as it progresses northwards.
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| Map of the study area north and northwest of Svalbard. Black arrows show the individual ice drifting experiments included in this study and the large red arrow indicate the pathways of the West Spitsbergen Current along the coast of Svalbard, transporting warm and salty Atlantic water into the Arctic. |
Large heat loss over shallow water
A new study published in Journal of Physical Oceanography by the Bjerknes researhers Anders Sirevaag and Ilker Fer presents observations from several drifting ice stations in the area north of Svalbard. The drift stations, which took place in early spring in the years 2003 – 2007, contain direct measurements of heat fluxes and amounts of mixing within the water column. The measurements that were made within the main branches of the WSC or over the shelves close to Svalbard show large heat fluxes and mixing due to strong currents and impact of strong tides and shallow topography.
The measurements made outside the WSC and far off the shelves, show heat exchange and mixing rates similar to observations made within the central Arctic Ocean. The results also show that in the area north of Svalbard, water masses are more modified by heat loss to the atmosphere than by ice melting. The study emphasizes the importance of mixing along the boundaries and over shelves and topography for the cooling of the relatively warm water that flows into the Arctic.