Changing Sea Ice in the Nordic Seas and its Effect on Water Mass Transformation

The physical processes that take place in the Nordic Seas, the gateway between the Atlantic and the Arctic Oceans, are important for the world’s oceans and climate. Waters transformed in the Nordic Seas form the lower limb of the Atlantic Meridional Overturning Circulation and impact the transport of heat to high northern latitudes. The Nordic Seas are both responding to and affecting a climate in change, both for the present and the past. However, it is not yet clear why, how, and to what extent the Nordic Seas are changing. Here, we study climatic changes in the Nordic Seas related to sea ice over a range of different timescales using an eddy-resolving configuration of the Massachusetts Institute of Technology general circulation model.

By employing a configuration with idealized topography we demonstrate the potential for an extensive sea-ice cover in the Nordic Seas during colder climates, consistent with paleoclimatic reconstructions. The sea-ice cover is found to be highly sensitive to changes in Atlantic water temperature and freshwater input: small changes in oceanic forcing lead to large and abrupt changes in sea ice and ocean circulation. A more extensive sea-ice cover in the Nordic Seas than today shuts down convection and reduces the heat loss from the Atlantic waters circulating the basin. The waters exiting the Nordic Seas are therefore warmer in a colder climate.

The current change in sea ice also affects convection and Atlantic water transformation in the Nordic Seas; observations have shown a re-ventilation of the Atlantic water in a warming climate. We address ongoing changes in the Nordic Seas using a model configuration with realistic topography as well as initial and boundary conditions that represent distinct periods over the past few decades.