A Role for the Ocean in the Winter Sea Ice Distribution North of Svalbard

Abstract

The ocean is suggested to play a major role in the ongoing winter decay of the sea ice cover in the western Eurasian Basin. Using a high-resolution sea ice-ocean model, we investigate the processes influencing the ice-ocean interactions in winter in the waters north of Svalbard, with a particular focus on those contributing to sea ice melt events of large amplitude. These short term events, lasting 5–10 days, are associated with locally large melt rates mostly found along the pathway of the Atlantic Water. The sum of all these events over the simulation period is found to contribute 40% of the total winter melt. Episodes of strong surface winds, occasionally associated with enhanced velocity shear at the mixed layer base, can trigger enhanced entrainment of Atlantic Water through the relatively shallow upper thermocline in the Atlantic Water boundary current, leading to substantial ocean heat transfer to the sea ice. In some cases, strengthening of the boundary current also contributes to fueling the heat transfer to the ice. Another type of large melt event, not linked to increased ocean vertical heat flux but due to ice being advected over warm surface waters, is also identified, sometimes associated with episodes of ice close-up. Sea ice budget calculations show that, overall, large melt events contribute significantly to the eastward retreat of the winter marginal ice zone on the upper slope east of Svalbard while episodes of northward advection of ice largely dominate the ice edge retreat over the shelf north of Svalbard.