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

世界各地的海平面目前正在上升，洪水和侵蚀加剧威胁着沿海人口，评估未来的威胁需要有能力预测海平面的变化。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，我们知道部分冰盖正在变薄。最快的变化发生在冰盖边缘附近，在那里流入大海的地方被称为松岛湾，变化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图像并不完全是错的。气温永远不会上升到冰点以上，但在寒冷的海面下，水温会上升到1摄氏度，远远高于冰点。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，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。不难理解，温水会导致快速融化，但究竟什么叫“暖”和“快”呢？如果我们把水温改变一点，融化速度会改变多少？最重要的是，什么可能会导致海洋温度的变化？为了找到这些问题的答案，我们必须测量冰川下面的水温，同时测量冰川底部融化到海洋中的速度，但这样做是非常具有挑战性的。冰川厚度在300米到1公里之间，因此很难到达其底部。关键是尖端技术，即能够潜入冰层下的机器人潜艇，沿着预先定义的轨迹进行测量，然后带着数据返回表面，以及一套坚固的自主雷达系统，可以在整个南极冬季留在冰川表面，精确测量冰层厚度的变化速度。机器人潜艇由NERC工程师设计和制造，并已于2009年在松岛冰川下进行了初步任务。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--与仔细测量返回回波的相位相结合，以确定图像中独特特征的位置，如冰川底部，在1公里范围内具有1毫米量级的非常高的精度。其中四台雷达仪器将留在松岛冰川表面，设计成可以全年自主运行，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和冰川以北海域中的水流。利用这个模型，我们将确定洋流输送到洞穴中的热量是如何被用来融化冰架的，以及南极这一地区气候的变化将对洋流和由此产生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，从而将如何影响这一世界偏远地区未来的海岸线，如荷兰和东英吉利。

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.