As the climate changes, so does the face of local meteorology. In the Arctic it appears the Beaufort high is gradually making place for increased dominance of low pressure systems, leading to a more dominant positive phase in the Arctic Oscillation (AO). And this in turn may have large climatic relevance…
Under a positive AO northern hemisphere westerlies pick up and Russian Arctic waters come under increasing Atlantic influence – with a wind-driven current of warm and salty water spreading eastwards along the coast.
Although this speeds up ice melting along the Eurasian coasts, it may also help save some sea ice in the North American Arctic – and the stability of the Gulf Stream.
The situation is summarised in the above salinity anomaly chart [between 2005-2008] that was presented yesterday by NASA and the University of Washington, and which indicates the counter clockwise surface current continues eastwards, then at some point connects to the clockwise Beaufort Gyre, jumping across to accumulate extra fresh water in the Canadian Arctic.
The researchers, who have published their findings in Nature, say on the whole the salinity of the Arctic Ocean hasn’t changed much. The local differences are however large: in the Beaufort Sea the water is now thought to be fresher than anywhere in the last 50 years, with especially the extra fluvial input adding about 3 meters of fresh water to that part of the Arctic Ocean.
Because of high stratification between light fresh water and denser salt water beneath this situation may be preserved under seasonal changes, slowing down spring thaw and speeding up winter refreezing – in the Canadian Arctic.
In the Russian Arctic of course the situation would be the opposite, with more saline waters promoting ice loss. As also along the Arctic margins of the Greenland Sea and the Barentz Sea the water seems to be getting saltier – in words of the press release – ‘allays concerns‘* over a freshwater Arctic destabilising the thermohaline circulation.
[*) These concerns have been slowly diminishing over recent years anyway, as ocean thermohalinity models show little response to a (seeping) fresh water influx and for instance new research indicates the North Atlantic waters may be rather flexible at chosing a spot to sink. Moreover, we may even have lost our ice age worst case scenario.]
[*) Perhaps a bigger global climate concern should be the Russian tundra swamps. In that case the implications of the NASA study are not as positive. Less offshore ice and decreased albedo in combination with a stronger west circulation can only further promote permafrost thaw in the Eurasian Arctic – and probably also in Alaska. So let's hope no more than 62 gigatonnes of carbon (2011 PNAS projection) are released from Arctic tundra soils this century – and let’s indeed hope this will be in the form of CO2.]
© Rolf Schuttenhelm | www.bitsofscience.org