Ocean Circulation and Ice Shelf Melting on the Amundsen Sea Continental Shelf

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Sea levels around the world are currently rising by about 2 mm every year. That may not sound very much, but people living in areas such as Holland or East Anglia are already threatened by coastal erosion. If we are to say how that threat might change in the future we must learn how to forecast changes in sea level. To do this we must understand what is happening to the Earth's great reservoirs of freshwater, and whether or not they are slowly draining into the ocean. The largest of these reservoirs by far is the Antarctic Ice Sheet, which contains 70% of all the freshwater on the planet. At present we do not know whether the ice sheet is growing or shrinking overall, but we do know that some parts of it are getting smaller. The fastest changes are happening at the edge of the ice sheet, where it flows into the sea, in a place called Pine Island Bay. Nobody yet knows what is causing these changes, and their speed has taken scientists by surprise. Pine Island Bay is geographically the far south of the Pacific Ocean, and the image of warmth that this conjures up is not entirely misplaced. The air temperatures never rise above freezing and the coast is battered by storms, but beneath the cold surface of the sea, water temperatures rise as high as 1 degree Celcius. This may seem cold by our standards (sea temperatures around Britain rarely drop into single figures, even in winter), but it is warm enough to melt the ice. Pine Island Glacier is a vast river of ice that flows out into Pine Island Bay. It carries as much water as the River Rhine, but in frozen form. The last 75 km of the Glacier floats on the waters of Pine Island Bay, and the bottom melts so intensely that half of the ice carried in the glacier is lost within the space of 30 years. The other half breaks off the end of the glacier as icebergs, which drift away to melt elsewhere. It is not hard to understand that warm water causes rapid melting, but what do 'warm' and 'rapid' really mean? If we change the water temperature by a small amount, by how much will the melt rate change? To find the answers to those questions we must make measurements of the water temperature beneath the glacier, but to do so is enormously challenging. The glacier is between 300 m and 1 km thick, so we cannot get instruments through from above, while the drifting Antarctic pack ice bars access to the front of the glacier to all but the most powerful ships. Engineers working at the Southampton Oceanography Centre have, over many years, designed and built a solution to this problem in the form of a robotic submarine that they can programme to dive beneath the ice, make measurements along a pre-defined track, then return to the surface with the vital data. By teaming up with American scientists, who can make use of a powerful icebreaker, we hope to take the submarine right up to Pine Island Glacier and launch it on its mission beneath the ice.The underwater cavern beneath the glacier is completely unknown and the submarine must find its own way in and out, avoiding any obstacles that it finds along its path. The Antarctic pack ice is notoriously unpredictable and could prove a huge challenge to the ship. But the potential return makes the risks worthwhile. Armed with our new knowledge we will build a computer model that describes the flow of water within the remote cavern beneath the glacier and in the sea to the north of it. Using this model we will determine if there have been any changes in the water temperature in Pine Island Bay over the past 20 years and how such changes would have affected melting of the glacier base. Other scientists can then use our results to establish if changes in the glacier's melt rate could have caused the ice sheet to thin in the way that has been observed, and together we will be able to say with greater certainty what impact the glaciers of Pine Island Bay will have on the future coastlines of Holland and East Anglia.