Thinner Arctic sea ice may affect global ocean circulation

The weakening of the AMOC, Atlantic Meridional Overturning Circulation, is a hot topic among the world's climate scientists. However, it is unclear what the consequences will be when the ocean currents change and when a tipping point is reached. Researcher Céline Heuzé from the University of Gothenburg, together with colleagues Marylou Athanase and Raphael Köhler from Germany, has studied the future of one of the major ocean currents in the Beaufort Sea, located in the Arctic Ocean, north of the Alaskan and Canadian coasts.

This current is the Beaufort Gyre and it is an important feature of the Arctic Ocean. By storing or releasing freshwater, it influences the oceanic properties both within the Arctic and as far away as the North Atlantic.

Due to warmer temperatures in the Arctic, the Beaufort Gyre is currently losing large amounts of sea ice. The ice helps keeping the ocean cool, acting as a lid. Thinner sea ice allows more heat from the atmosphere to pass through, raising sea temperatures further and causing even more sea ice to disappear. Previous research shows that the freshwater content of the Beaufort Sea has increased by 40 percent over the last two decades.

Concerns about sea ice 'tipping point'

"The results of this study make us concerned that the reduction of sea ice in the area could lead to a tipping point where the AMOC collapses," says Céline Heuzé, Senior Lecturer in Climatology at the University of Gothenburg and an expert on deep ocean and sea ice.

In the study, the researchers made projections using only the global climate models that can accurately represent the Beaufort Gyre. A climate model is a computer simulation of the Earth's climate system -- atmosphere, ocean, land and ice. Climate models are used to reconstruct the past climate or predict the future climate.

"If greenhouse gas emissions are not reduced urgently, this projection suggests that the Beaufort Gyre will weaken and release the freshwater that it currently holds. This freshwater could then reach the North Atlantic and possibly negatively impact the AMOC," says Marylou Athanase, researcher at Alfred Wegener Institute, Germany, and first author of the study.

The AMOC, of which the Gulf Stream is a part, is of great importance for the climate in Scandinavia as it transports warm water to high latitudes in the northern hemisphere. How the link between reduced Arctic sea ice and a weakening of the AMOC may develop in the future is something the researchers now want to study more closely.

Background information

The Gulf Stream and the AMOC

The ocean circulation in the Atlantic that many climate scientists focus on is called the AMOC -- Atlantic Meridional Overturning Circulation. It is a large system of ocean currents in the Atlantic, of which the Gulf Stream is a part. The AMOC system is driven by differences in density between different water masses so that warm water from more southerly latitudes moves north along the ocean surface where it cools, sinks and moves south again into the deep ocean. (Wikipedia)

Tipping points

In climate science, a tipping point is a critical threshold that, when crossed, leads to large, accelerating and often irreversible changes in the climate system. (Wikipedia)