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

目前，全球海平面正以每年约2毫米的速度上升。这听起来可能不是很多，但生活在荷兰或东英吉利等地区的人们已经受到海岸侵蚀的威胁。如果我们要说这一威胁在未来可能如何变化，我们就必须学会如何预测海平面的变化。要做到这一点，我们必须了解地球上巨大的淡水水库正在发生什么，以及它们是否正在缓慢地排入海洋。到目前为止，这些水库中最大的是南极冰盖，它包含了地球上70%的淡水。目前我们不知道整个冰盖是在扩大还是在缩小，但我们知道冰盖的某些部分正在变小。最快的变化发生在冰盖的边缘，在那里它流入大海，在一个叫松岛湾的地方。目前还没有人知道是什么导致了这些变化，它们的速度让科学家们感到惊讶。松岛湾在地理上位于太平洋的最南端，这让人联想到温暖的形象，这并不完全是错的。气温永远不会超过冰点，海岸被暴风雨袭击，但在寒冷的海面下，水温最高可达1摄氏度。按照我们的标准，这可能看起来很冷(英国周围的海温很少降到个位数，即使在冬天也是如此)，但它足够温暖，足以融化冰层。松岛冰川是一条巨大的冰河，流入松岛湾。它输送的水量和莱茵河一样多，但都是冰冻的。冰川的最后75公里漂浮在松岛湾的水面上，冰底融化得如此剧烈，以至于冰川携带的冰有一半在30年内消失了。另一半冰川的末端破裂为冰山，冰山漂移到其他地方融化。不难理解，温水会导致快速融化，但“温暖”和“迅速”的真正含义是什么？如果我们把水温改变一点，融化速度会改变多少？为了找到这些问题的答案，我们必须测量冰川下的水温，但这样做是巨大的挑战。冰川厚度在300米到1公里之间，所以我们无法从上面通过仪器，而漂浮的南极冰川覆盖着冰块，除了最强大的船只外，所有人都可以进入冰川前面。多年来，在南安普顿海洋学中心工作的工程师们设计并建造了一种机器人潜艇的形式来解决这个问题，他们可以对潜艇进行编程，在冰下潜水，沿着预先定义的轨迹进行测量，然后带着关键数据返回海面。通过与美国科学家合作，他们可以利用强大的破冰船，我们希望将潜艇直接带到松岛冰川，并在冰层下发射它执行任务。冰川下的水下洞穴完全未知，潜艇必须自己找到进出的路，避开沿途发现的任何障碍。南极的浮冰是出了名的不可预测，可能会给这艘船带来巨大的挑战。但潜在的回报让风险变得值得。有了我们的新知识，我们将建立一个计算机模型，描述冰川下方偏远洞穴内和冰川以北海域中的水流。利用这个模型，我们将确定在过去的20年里，松岛湾的水温是否有任何变化，以及这种变化将如何影响冰川底部的融化。然后，其他科学家可以利用我们的结果来确定冰川融化速度的变化是否会导致冰盖以观察到的方式变薄，我们将能够更确定地说，松岛湾的冰川将对荷兰和东英吉利群岛未来的海岸线产生什么影响。

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.