April 6, 2011

Arctic Fresh Water Could Alter Europe’s Climate

Oceanographers are monitoring a vast expanse of fresh water in the Arctic Ocean that could spill into the Atlantic, something that could result in unpredictable changes in the ocean currents that give Western Europe its moderate climate.

The scientists said Tuesday that the unusual accumulation of fresh water resulted from the Siberian and Canadian rivers dumping more water into the Arctic, and from melting sea ice.

"The volume of water discharged into the Arctic Ocean, largely from Canadian and Siberian rivers, is higher than usual due to warmer temperatures in the north causing ice to melt," Laura De Steur of the Royal Netherlands Institute for Sea Research said in a statement.

"Sea ice is also melting quickly "“ another new record low for ocean area covered was recently documented by the National Snow and Ice Data Center, adding even more freshwater to the relatively calm Arctic Ocean,"

If it should spill into the Atlantic Ocean, the addition of so much fresh water could alter the ocean current that brings warmth from the tropics to European shores, she added.

The Arctic Ocean's fresh water content has risen 20 percent since the 1990s, or about 8,400 cubic kilometers -- the volume of all the water in Lake Michigan and Lake Huron combined, said German researcher Benjamin Rabe of the Alfred Wegener Institute.

Increased runoff from the great northern rivers "could potentially impact the large scale ocean circulation in the Atlantic Ocean," said De Steur.

"This is important for us in Western Europe because our climate is pretty much dictated by the Thermohaline ocean circulation," she said, referring to the system of deep ocean and wind-driven currents, such as the Gulf Stream, which carries warmth from the tropics.

The Thermohaline current loops from the tropics to the North Atlantic, powered by differences in salt content and wind patterns.  Warm water from the south increases in salinity and grows heavier as it cools.  At its northern end, cold air further cools the current, which then sinks before warming again and rising as it travels south.

"Sea ice that is thinner is more mobile and could exit the Arctic faster. In the worst case, these Arctic outflow surges can significantly change the densities of marine surface waters in the extreme North Atlantic. What happens then is hard to predict," De Steur said.

Most of the excess fresh water has collected in the Canada Basin, she added.  However, during the last three years changes also have been observed in the Eurasian side of the Arctic Ocean.

The icy water has until now been held in the Arctic Ocean by wind patterns, which have not shifted their general clockwise direction for 12 years.  This is somewhat atypical; these winds have historically changed at intervals of five to ten years.

"It's important to monitor this to see if this can be transported to the Atlantic, where it might potentially affect the Gulf Stream and the Thermohaline circulation," De Steur said.

Rabe warned that the results of model simulations are inconclusive, and that scientists have not been studying the matter long enough to predict what may happen in the future.

The Guardian newspaper reported on Tuesday that freshwater inflow from rivers could also impact the Baltic Sea.  Its salinity is determined by the amount of freshwater flowing off the surrounding land, and how much water is exchanged with the North Sea, said Thomas Neumann of Germany's Leibnitz-Institute for Baltic Sea Research. If the salinity declined further, it could potentially harm the species that live there.


Image Caption: Polar stratospheric clouds in the Arctic. Photo: Ross J. Salawitch, University of Maryland


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