The spin-up of the Arctic Ocean

The Earth is currently undergoing the largest climate experiment in history. Our climate system is in a state of change and the most dramatic sign of that change is the shrinking of the Arctic sea ice cover. As ice melts, less heat from the sun is reflected back into space, so the warming in the polar regions increases, melting more ice. This positive feedback is well understood. However, as the Arctic ice cover retreats the Arctic Ocean circulation will also change radically, which may result in additional changes, both to the ice cover and to the way fresh water from rivers and melting ice work to dilute the sea water. The dilution of sea water can eventually change the ways that the warm Atlantic Ocean brings heat to northern Europe (and the UK). This proposal will explore how the Arctic Ocean circulation is changing due to the retreating ice cover using novel satellite techniques, in-situ data and models. 'Spin-up' refers to what happens to the ocean when the wind acts on it. For example, in the Arctic, if the wind were blowing in a clockwise (anti-cyclonic) sense - like the winds around a mid-latitude high pressure system - then the ocean waters would be pushed towards the location of the centre of the high, causing a hill in the sea level. The ocean the responds to this by flowing in the same direction as the atmospheric isobars: i.e. the wind is spinning up the ocean. Sea ice forms a boundary between the atmosphere and the ocean, greatly reducing the effect of the force of the wind on the ocean. So as the ice retreats we expect the wind to act more efficiently on the ocean and spin it up, which will change the circulation of the Arctic Ocean. This change in the circulation may act to cool the climate of Northern Europe. The Arctic Ocean both contains a large amount of fresh water, and also can act as a conduit for much more (from rivers and ice melt), which if released has the potential to disrupt the global ocean circulation and cool the climate of Northern Europe. If the Arctic Ocean spins up, this will change the ocean circulation and hence may change the storage of the freshwater and its export out of the Arctic Ocean into the North Atlantic. The change in circulation may also cause in an additional positive feedback to the retreat of the ice cover. The Arctic Ocean has a cold, fresh surface layer with warmer, saline Atlantic water below. These two layers don't mix much with each other, which means that sea ice can easily grow in the cold surface layer during the winter. When the wind blows on the ocean the water below is stirred up. So if the force of the wind on the ocean increases, due to the retreat of the ice cover, there will be increased mixing between the warm Atlantic layer and the cool fresh layer, resulting in heat being transported into the cool layer. It is estimated that an enhanced upward heat flux could reduce the growth of sea ice in winter by 70-80%. Work at University College London, using data from European Space Agency (ESA) satellites, means that we can now measure the hills in the sea level caused by the spin-up of the ocean and answer the question of what will happen to the ocean circulation as the ice cover retreats. It has not been possible to attempt this research in the past as the satellite data set needed to explore these questions has not existed due to the difficulty in making measurements over the sea ice. In addition, the launch of the new ESA satellite CryoSat2, in February 2010, means that there will soon be an even better data set to address these important questions of environmental change in the Arctic.