Ocean circulation and melting beneath the ice shelves of the south-eastern Amundsen Sea

目前世界各地的海平面都在上升，洪水和侵蚀加剧威胁着沿海地区的人口，评估未来的威胁需要有预测海平面变化的能力。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，以及它们是否正在慢慢流入海洋。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，我们知道冰盖的一部分正在变薄。最快的变化发生在冰原边缘附近，那里有一个叫做松岛湾的地方流入大海，变化的速度让科学家们感到惊讶。松树岛湾在地理上位于太平洋的最南端，这让人联想到的温暖的形象并非完全错位。空气温度从未超过冰点，但在寒冷的海面下，水温上升高达1摄氏度，远高于冰点。松岛冰川是一条巨大的冰河，流入松岛湾，携带的水量与冰冻的莱茵河一样多。冰川的最后60公里漂浮在松岛湾的水面上，底部融化得如此剧烈，以至于冰川携带的一半冰在30年的时间里消失了。温水导致快速融化并不难理解，但“温暖”和“快速”究竟是什么意思呢？如果我们稍微改变水温，融化速率会改变多少？关键的是，是什么导致了海洋温度的变化？为了找到这些问题的答案，我们必须测量冰川下的水温，同时测量冰川底部融化到海洋中的速度，但这样做是极具挑战性的。冰川的厚度在300米到1公里之间，因此很难进入它的底部。关键在于尖端技术，即一艘能够潜入冰下的机器人潜艇，沿着预先设定的轨道进行测量，然后带着数据返回水面，以及一套坚固的自主雷达系统，这些系统可以在整个南极冬季留在冰川表面，精确测量冰厚变化的速度。机器人潜艇由NERC工程师设计和建造，并于2009年在松岛冰川下的初步任务中证明了自己。雷达系统将作为该项目的一部分进行开发。他们将结合一种著名的雷达技术——FMCW雷达，仔细测量返回回波的相位，以确定图像中独特特征的位置，例如冰川底部，在1公里范围内具有非常高的精度，约为1毫米。其中四台雷达仪器将留在松岛冰川的表面，经过设计，可以全年自主运行，并监测冰层厚度随时间的逐渐变化。有了这些新仪器的数据，我们将使用一个计算机模型来描述冰川下方偏远洞穴内以及冰川北部海洋中的水流。利用这个模型，我们将确定洋流输送到洞穴中的热量如何被用来融化冰架，以及南极这部分地区的气候变化将对洋流和由此导致的融化速度产生什么影响。这些信息将使其他人能够更确定地评估未来气候变化将如何影响松岛湾的冰川，从而评估世界上这个偏远地区将如何影响荷兰和东安格利亚等地的未来海岸线。

Sea levels around the world are currently rising, threatening coastal populations with flooding and increased erosion, and evaluating the future threat requires an ability 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, and we know that parts of the ice sheet are thinning. The fastest changes are happening near the edge of the ice sheet, where it flows into the sea in a place called Pine Island Bay, and the speed of the changes 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, but beneath the cold surface of the sea, water temperatures rise as high as 1 degree Celsius, well above the freezing point. Pine Island Glacier is a vast river of ice that flows out into Pine Island Bay, carrying as much water as the River Rhine in frozen form. The last 60 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. 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? And critically, what might cause the ocean temperature to change?To find the answers to those questions we must make measurements of the water temperature beneath the glacier, and simultaneous measurements of the rate at which the base of the glacier is melting into the ocean, but to do so is enormously challenging. The glacier is between 300 m and 1 km thick, so it is difficult to access its base. The key is cutting-edge technology, in the form a robotic submarine capable of diving beneath the ice, making measurements along a pre-defined track, then returning to the surface with the data, and a set of rugged, autonomous radar systems that can left on the glacier's surface throughout the Antarctic winter precisely measuring the rate at which the thickness of the ice changes.The robot submarine has been designed and built by NERC engineers and has already proved itself on preliminary missions beneath Pine Island Glacier in 2009. The radar systems will be developed as part of this project. They will combine a well-known radar technique, FMCW radar, with careful measurement of the phase of the return echoes to establish the position of unique features in the image, such as the bottom of the glacier, with very high precision of the order of 1 mm over a 1 km range. Four of these radar instruments will be left on the surface of Pine Island Glacier, engineered to allow year-round autonomous operation and monitoring of the gradual change of ice thickness with time. Armed with the data from these new instruments we will use 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 how heat that is transported into the cavern by ocean currents is used to melt the ice shelf and what impact changes in the climate of this part of Antarctic will have on the ocean currents and resulting melt rates. This information will allow others to assess with greater certainty how future climate change will impact the glaciers of Pine Island Bay and hence how this remote part of the world will influence the future coastlines of places such as Holland and East Anglia.