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

山脉冰川是二十世纪测量的海平面上升的主要来源，也是目前海平面上升的原因。南极半岛是一个主要的山地冰川系统，有400多个冰川，几乎所有的冰川都流入大海。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贡献与阿拉斯加、加拿大北极、巴塔哥尼亚和斯瓦尔巴尔群岛等其他快速变化的近极或大型山地冰川环境的速度相似。冰川融化或冰山在冰川前部崩解的增加导致冰川冰流失到海洋中，从而导致海平面上升。研究了20世纪南极半岛冰川长度和冰架面积的变化，已知许多冰川加速。然而，几乎没有关于冰川中所含冰量变化的信息。因此，目前对山脉和近极冰川在过去海平面变化中的作用的评估没有适当地将南极半岛包括在内。预测南极半岛冰盖未来对海平面的影响首先需要了解过去和最近的冰川质量变化。现在测量这些冰川质量过去变化的唯一方法是通过历史上的航空摄影进行详细的三维测量。南极半岛北部有3万多张合适的航拍照片，可以追溯到20世纪50年代，有些地方在这段时间里拍摄了几张照片。它们最初是为了测绘和绘制海岸的水文图而飞行的。我们的研究将集中在50年内50个冰川的质量变化。我们将使用摄影测量法，这是一种由航空摄影制作地图和土木工程测量的成熟方法，用于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消融的地理范围，并揭示随着时间的推移冰川消融加速等趋势。它还将确定，在冰川上部，由于降雪量增加，海岸附近的冰川融化是否会被增加所抵消。使用摄影测量学从旧照片中进行可靠的测量依赖于准确地将已知的地面测量点与它们在照片上的位置相关联。对于南极半岛来说，这样的地面控制点一直很难获得，而且根本不存在所需的数量。到目前为止，这阻止了从照片中进行测量，这些照片是一种未开发的资源。项目组开发了一种新技术，将从旧照片测量的表面与最近的卫星图像或全球定位系统支持的航空摄影联系起来，消除了实地勘测地面控制的需要。它允许我们从航空照片档案中解锁冰川变化的测量结果，并建立一套由50个基准冰川组成的套件，这些冰川具有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，将它们用作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，或者海洋温度和海冰覆盖等其他因素是否也是驱动因素。总体而言，该项目将把南极半岛从几乎没有测量到的变化转变为最著名的大型山脉或近极冰川系统之一，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.