The changing seasonal cycle of the Arctic Ocean

The seasonal cycle of Arctic Ocean temperature is weak due to the insulating and light scattering effects of sea ice cover and the moderating influence of the seasonal storage and release of heat through ice melting and freezing. The retreat of sea ice and other changes in recent decades is already warming surface air temperatures in winter. We our analysis of future change with an examination of the dominant processes in the seasonal response of the Arctic Ocean and sea ice to surface forcing as they appear in historical simulations of 14 CMIP5 climate models. In both models and observations the seasonal heat budget is dominated by a local balance between net surface heating and storage in the heat content of the ocean and in melting/freezing of sea ice. Observations suggest ocean heat storage is more important than sea ice melt, while in most models sea ice melt dominates. The dominant balance in the seasonal freshwater budget is the exchange of freshwater between the liquid ocean and sea ice. At its peak this rate of exchange exceeds 2Sv. The appearance of sea ice and also ocean stratification in both the heat and freshwater budgets provides two links between the budgets and two mechanisms for feedback. Our analysis of the seasonal cycle in the coming centuries suggests that the loss of sea ice will dramatically increase the amplitude of the seasonal cycle of sea surface temperature in the Arctic Ocean. Depending on the rate of growth of atmospheric greenhouse gases the seasonal range in Arctic sea surface temperature may exceed 10°C by year 2300, greatly increasing the stratification of the summer mixed layer.