The heat budget of the Nordic seas: insights from a 1/12° coupled ocean-atmosphere-ice model

The Nordic Seas are a region of deep water formation, a major control of the Atlantic Meridional Overturning Circulation and a gateway to the Arctic Ocean. In the east of the Nordic seas (Norwegian sea), the ocean loses heat to the atmosphere. In the western part of the Nordic seas, in the Greenland and Iceland seas, the surface conditions are very different due to the seasonal ice cover, and the heat loss experienced by the ocean cannot be observed directly. The balance of this surface heat loss by ocean convergence of heat is difficult to quantify from observations. In recent years, coupled climate models have been developed with ocean components at higher resolution, such as the high resolution version of the Met Office Global Coupled Model GC3 based on the GO6 configuration of the ORCA12 1/12° ocean model. Coupled models represent ice-ocean-atmosphere interactions in a more consistent manner than ocean-ice models forced by a fixed atmospheric state. For the first time we use such a model to compute the heat budget in the Nordic seas. The GC3 model reproduces the contrasted ocean heat loss between the eastern and western regions. Integrated over the Greenland and Iceland seas, the heat loss experienced by the ocean is close to the atmospheric heat gain of the ERA5 reanalysis, because of a compensating effect between the insulating effect of sea ice and the cooling by ice melt. The latter is a major contribution to the heat loss over the path of the East Greenland Current. The model indicates a balance between surface fluxes and ocean heat convergence due to exchanges with the North Atlantic, the Barents Sea and the Arctic, in each of the eastern and western regions. The net heat exchange between these two regions, integrated from Fram Strait to Iceland, is relatively small. Eddy and other time fluctuations contribute to the net heat transports. Their contributions exceed 20% in Denmark Strait and across the Knipovich ridge.