Sea ice decline could weaken ocean currents of the North Atlantic

The research, published in Nature Climate Change and conducted in partnership with Yale University, found that a decline in sea ice cover caused by global warming could weaken the Atlantic Meridional Overturning Circulation (AMOC) – a large-scale ocean circulation system that affects climate.

AMOC is responsible for transporting heat from low to high latitudes. It has a lower limb of dense, cold water that flows south from the North Atlantic, and an upper limb of warm, salty water that flows north from the South Atlantic as part of the Gulf Stream.

The authors found that the system – which plays a major role in the climate of Atlantic rim countries, particularly those in Europe – could lose up to 50 per cent of its strength, leading to a cooling of the ocean surface in parts of the North Atlantic.

Lead author Dr Florian Sévellec, of the University of Southampton, said: “We suggest that Arctic ocean changes on a multi-decadal time scale, such as the decline in sea ice cover that we are currently experiencing, can efficiently weaken the large-scale ocean circulation of the North Atlantic, which is responsible for the oceanic transport of heat from the Equator to high latitudes.

“This in turn would have significant impacts on our daily weather, since the slow-down of this circulation, and its induced ocean surface cooling, has been shown in other studies to lead to an increase in storminess, to harsher winters, and to drier summers in Europe, for instance.”

Co-author Professor Alexey Fedorov, of Yale University, added: “Our study establishes a new mechanism that links the loss of sea ice and the AMOC. Potentially, this mechanism could lead to a reduction of between 30 and 50 per cent of the AMOC’s strength.”

In the short term, changes in the subpolar North Atlantic have the greatest impact on AMOC, the researchers found. But over the course of a few decades, it was changes in the Arctic that became most important to AMOC.

The researchers based their findings on a combination of comprehensive climate change model simulations and novel computations of the sensitivity of ocean circulation to fluctuations in temperature and salinity at the ocean’s surface over time.

The research was supported by grants from the Natural and Environmental Research Council UK, the US Department of Energy Office of Science, and the National Oceanic and Atmospheric Administration.