Abstract
Broad, long-living, ice-free areas in mid-winter northeast of Svalbard between 2011 and 2014 are investigated. The formation of these persistent and re-emerging anomalies is linked, hypothetically, with the increased seasonality of Arctic sea ice cover, enabling an enhanced influence of oceanic heat on sea ice, and in particular, heat transported by Atlantic Water. The ‘memory’ of ice-depleted conditions in summer is transferred to the fall season, through excess heat content in the upper mixed layer, which in turn transfers to mid-winter via thinner and younger ice. This thinner ice is more fragile and mobile, thus facilitating the formation of polynyas and leads. When openings in ice cover form along the Atlantic Water pathway, weak density stratification at the mixed layer base supports the development of thermohaline convection, which further entrains warm and salty water from deeper layers. Convection-induced upward heat flux from the Atlantic layer retards ice formation, either keeping ice thickness low or blocking ice formation entirely. Certain stages of this chain of events have been examined in a region north of Svalbard and Franz Joseph Land, between 80-83°N and 15-60°E, where the top hundred meters of Atlantic inflow through the Fram Strait cools and freshens rapidly. Complementary research methods, including statistical analyses of observations and numerical modelling, are used to support our basic concept that the recently observed retreat of sea ice northeast of Svalbard in winter may be explained by a positive feedback between summer ice decay and the growing influence of oceanic heat on a seasonal time scale.
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