Turbulence changes Arctic's role in climate change
6 April 2011, by Adele Walker
The loss of sea ice in the Arctic Ocean caused by a warming environment could be made worse by previously undetected turbulence, which has been identified by scientists from Bangor University.
Arctic sea ice.
Until now the Arctic Ocean was thought to be relatively tranquil. But observations by an international team, lead by Yueng-Djern Lenn of Bangor's School of Ocean Sciences, show for the first time that different water layers are being mixed together by bursts of turbulence beneath the Arctic ice.
Turbulence is caused by the action of the wind on the sea and ice; ice cover averages out the wind's effect, but when there is no ice the wind acts directly on the sea. When the wind blows in the opposite direction to the flow of water the turbulence is greatly increased.
This mixing brings heat from the ocean interior up to just beneath the ice, while in open water it takes the warmth of the summer sun from the surface water layers and carries it down to deeper water.
So the strength and frequency of this mixing could have a significant effect on how much ice cover there is in the Arctic itself.
It's such a huge event – if you missed it your results would be wrong by orders of magnitude.
Dr Tom Rippeth, Bangor University
According to these new findings, there is a lot more of this mixing when there is no sea ice insulating the sea surface from the atmosphere, which suggests that the Arctic Ocean will become more turbulent as the world gets warmer and sea ice retreats.
'These results are highly significant as they are helping us to understand the role of sea ice in the Arctic Ocean and in particular how it impacts heat exchange between the ocean interior and the atmosphere,' says Dr Tom Rippeth, co-author of the team's report which is published in the Journal of Physical Oceanography.
The profiler used to monitor the turbulence.
The team took made their observations from a Russian ice breaker, as part of an International Polar Year project. They measured what was happening in the water by lowering a profiler – essentially a long tube about 20cm diameter – vertically down into the water. Monitors inside the tube recorded the intensity of the turbulent eddies in the water that mix up the different layers.
The team had already seen changes in the water in the Arctic basin which couldn't be explained by the diffusion processes normally associated with mixing in the Arctic Ocean.
'We knew something was happening to this water,' says Rippeth, 'but the level of turbulence was a complete surprise. It's such a huge event – if you missed it your results would be wrong by orders of magnitude.'
So the team was in the right place at the right time. Based on their other work in the Irish and Celtic seas, they reckon such turbulence events are likely to be widespread at the edges of the Arctic Ocean.
'We are already seeing a big reduction in the extent of sea ice cover, particularly in the summer months, and so there is a lot more mixing going on,' says Rippeth.
'The question is, could the turbulence in summer increase to such an extent that it eventually prevents the sea ice reforming?' he continues.
Some scientists believe that we may already be feeling the effects of disappearing Arctic sea ice, through more serve winters, such as those endured during the past couple of winters here in the UK.
Yueng-Djern Lenn, Tom P Rippeth, Chris P Old, Sheldon Bacon, Igor Polyakov, Vladimir Ivanov and Jens Holemann. Intermittent intense turbulent mixing under ice in the Laptev Sea. (2010) Journal of Physical Oceanography doi: 10.1175/2010JPO4425.1
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