Is the “Atlantification” of the Arctic Ocean extending?

Abstract:

We present recent observation and modelling results, which suggest that retreat of the sea-ice edge in the Atlantic sector of the Arctic Ocean over several recent years may be an indication of the growing influence of Atlantic Water on the hydrographic regime (“Atlantification”). 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. The joint analysis of observations and modelling data is performed north-east of Svalbard 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, support our basic “Atlantification” concept. A general conclusion from the analysis performed is that the recently observed retreat of sea ice northeast of Svalbard in winter may be explained by the positive feedback between summer ice decay and the growing influence of oceanic heat on a seasonal time scale.