Ocean Science www.ocean-sci.net 1812-0784 1812-0792 6 1 2010 10.5194/os-6-401-2010 http://www.ocean-sci.net/6/401/2010/ http://www.ocean-sci.net/6/401/2010/os-6-401-2010.html http://www.ocean-sci.net/6/401/2010/os-6-401-2010.pdf 401 411 2010-03-22 Structure and forcing of the overflow at the Storfjorden sill and its connection to the Arctic coastal polynya in Storfjorden F. Geyer florian.geyer@nersc.no I. Fer L. H. Smedsrud Nansen Environmental and Remote Sensing Center, Thormølensgate 47, 5006 Bergen, Norway Bjerknes Center for Climate Research, Allégaten 55, 5007 Bergen, Norway Geophysical Institute, University of Bergen, Allégaten 70, 5007 Bergen, Norway Storfjorden (Svalbard) is a sill-fjord with an active polynya and exemplifies the dense water formation process over the Arctic shelves. Here we report on our simulations of Storfjorden covering the freezing season of 1999–2000 using an eddy-permitting 3-D ocean circulation model with a fully coupled dynamic and thermodynamic sea-ice model. The model results in the polynya region and of the dense water plume flowing over the sill crest are compared to observations. The connections of the overflow at the sill to the dense water production at the polynya and to the local wind forcing are investigated. Both the overflow and the polynya dynamics are found to be sensitive to wind forcing. In response to freezing and brine rejection over the polynya, the buoyancy forcing initiates an abrupt positive density anomaly. While the ocean integrates the buoyancy forcing over several polynya events (about 25 days), the wind forcing dominates the overflow response at the sill at weather scale. In the model, the density excess is diluted in the basin and leads to a gradual build-up of dense water behind the sill. 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