The spatial and temporal distribution of 20th Century Antarctic Peninsula glacier mass change and its drivers

山地冰川是20世纪测量到的海平面上升的一个主要来源，也是目前海平面上升的一个因素。南极半岛是一个主要的山地冰川系统，有400多个冰川，几乎所有的冰川都延伸到海洋。该地区气象站的记录显示，在过去的半个世纪里，该地区经历了夏季变暖。科学家们预计，南极半岛对海平面变化的影响与其他快速变化的近极地或大型山地冰川环境（如阿拉斯加、加拿大北极、巴塔哥尼亚和斯瓦尔巴群岛）相似。冰川前部的冰川融化或冰山崩解增加导致冰川冰流入海洋，导致海平面上升。人们对20世纪南极半岛冰川长度和冰架面积的变化进行了研究，已知许多冰川已经加速融化。然而，几乎没有关于冰川中冰量变化的信息。因此，南极半岛没有被适当地包括在目前对山地和近极地冰川在过去海平面变化中的作用的评估中。预测南极半岛冰盖对海平面的未来影响，首先需要了解过去和最近的冰川质量变化。现在测量冰川质量过去变化的唯一方法是通过历史航空摄影进行详细的三维测量。有一个超过30,000张适合的航空照片的档案，可以追溯到20世纪50年代的南极半岛北部，有些地方有这一时期的几个日期的报道。它们最初是用来绘制海岸的地图和水文图的。我们的研究将集中在50年时间跨度内50个冰川的质量变化。我们将使用摄影测量法，这是一种成熟的方法，可以通过航空摄影制作地图和土木工程测量，来绘制不同日期的冰川表面高程图。比较每个冰川的这些表面将显示冰川冰损失的地理范围，并揭示冰损失随时间的加速等趋势。它还将确定海岸附近的冰损失是否被冰川上部更高的降雪量所抵消。利用摄影测量法对旧照片进行可靠的测量，依赖于将精确已知的地面测量点与其在照片上的位置联系起来。对于南极半岛来说，这种地面控制点一直很难获得，而且根本没有所需的数量。到目前为止，这阻碍了对照片的测量，它们是一种未开发的资源。项目组开发的一项新技术将从旧照片中测量到的表面与最近的卫星图像或gps支持的航空摄影联系起来，消除了实地测量地面控制的需要。它使我们能够从航空照片档案中解锁冰川变化测量数据，并建立一套50个基准冰川，具有50年的记录，用于监测未来的变化。然后，我们将把测量到的冰川变化与气候记录联系起来，将它们作为项目团队开发的冰川行为计算机模型的参数。这将使我们能够分离出大气变暖在多大程度上解释了测量到的变化，或者其他因素，如海洋温度和海冰覆盖是否也是驱动因素。总的来说，该项目将把南极半岛从几乎无法测量的地方转变为最著名的大型山地或近极地冰川系统之一，并为大气变暖、降雪、海洋温度和海冰覆盖等变量在冰川质量变化中的作用提供新的见解。

Mountain glaciers are a major source of the sea-level rise measured in the twentieth century and contributor to present sea-level rise. The Antarctic Peninsula is a major mountain glacier system, with more than 400 glaciers, nearly all of which reach the sea. Records from weather stations in the area show that it has experienced summer warming over the last half-century. Scientists expect the Antarctic Peninsula to be contributing to sea-level change at a similar rate to that of other fast-changing near-polar or large mountain-glacier environments such as Alaska, the Canadian Arctic, Patagonia and Svalbard.Loss of glacier ice to the sea through melting or increased iceberg calving at the front of the glacier contributes to sea-level rise. Changes to the length of Antarctic Peninsula glaciers and area of its ice shelves in the twentieth century have been studied, and many glaciers are known to have speeded up. However there is almost no information on changes in the amount of ice contained in the glaciers. As a result, the Antarctic Peninsula is not properly included in current assessments of the role of mountain and near-polar glaciers in past sea-level change. Forecasting of the future impact of the Antarctic Peninsula ice sheet on sea level first needs an understanding of past and recent glacier mass changes. The only way to now measure these past changes in glacier mass is by detailed three-dimensional measurements from historic aerial photography. There is an archive of more than 30,000 suitable aerial photographs going back to the 1950s for the northern Antarctic Peninsula, and some places have coverage from several dates over this period. They were originally flown for mapping and hydrographic charting of the coast.Our research will focus on mass change of 50 glaciers over a 50 year-time span. We will use photogrammetry, a well-established method for making maps and civil-engineering measurements from aerial photography, to map the glacier surface elevation at different dates. Comparing these surfaces for each glacier will show the geographical extent of glacier ice loss and reveal trends such as acceleration of ice loss over time. It will also establish whether ice loss near the coast is counter-balanced by gain, from higher snowfall, in the upper parts of the glaciers. Making reliable measurements from the old photographs using photogrammetry relies on relating accurately-known ground surveyed points to their positions on the photographs. For the Antarctic Peninsula such ground-control points have always been difficult to obtain and simply do not exist in the numbers required. Until now, this has prevented measurements from the photographs and they are an unexploited resource. A new technique developed by the project team links surfaces measured from the old photographs to recent satellite imagery or GPS-supported aerial photography and eliminates the need for field-surveyed ground control. It allows us to unlock glacier change measurements from the archive of aerial photographs, and establish a suite of 50 benchmark glaciers, with a 50-year record, for monitoring future changes. We will then relate the measured glacier changes to the climate record, using them as parameters in a computer model of glacier behaviour developed by the project team. This will allow us to isolate the extent to which atmospheric warming, leading to increased melting, explains the measured changes, or whether other factors such as ocean temperature and sea ice cover are also drivers.Overall the project will transform the Antarctic Peninsula from being almost unmeasured to one of the best known large mountain or near-polar glacier systems and provide new insights into the roles of variables such as atmospheric warming, snowfall, marine temperature and sea-ice cover in glacier mass change.