Investigating meltwater flow beneath the Greenland Ice Sheet using a multi-tracer approach

格陵兰冰盖是北半球的主要冰库，能够影响21世纪的海平面。从飞机上测量冰盖表面的高度，现在可以更好地了解冰盖是否正在颗粒化或失去质量。然而，在更好地了解冰是如何从冰盖内部流向海洋之前，旨在预测格陵兰冰盖对气候变化的反应及其对海平面影响的模型不太可能产生准确的估计。冰流最不为人所知的一个方面是，冰盖底部的融水润滑可能会如何影响冰向海洋排放的速度。最近的研究表明，夏季地表融化水输入冰盖床会导致相当大的结冰速度。融水到底是如何在床上流动的(它是在离散的通道中流动，还是以更分散的方式扩散和流动？)对于理解冰盖可能如何应对气候变暖中融化输入的增加至关重要。目前，人们对基本熔水路线知之甚少，因为大量的熔水阻碍了传统示踪技术(如染料示踪)的使用。该项目旨在应用新的追踪方法，这种方法将在大规模稀释中幸存下来，并可以注入冰川表面的洞(山洞)中，并在冰盖前缘出现水时进行检测。其中一些技术已经在海洋学中被广泛使用，以追踪穿过海洋盆地的洋流。我们的示踪实验将提供有关冰盖底部融水流动路径特征及其时空变化的新信息，并提供沿流动路径特征的详细测量(例如压力)。将我们的示踪结果(如水流速度、渠道压力条件)与同一冰川的冰速数据进行比较，将有助于确定融水路线和冰流机制之间的联系，并将为未来旨在量化格陵兰冰盖对全球海平面上升的未来贡献的数值模拟研究生成一个独特的数据集。

The Greenland Ice Sheet is the main reservoir of ice in the northern hemisphere capable of affecting sea level in the 21st Century. Measurements of the elevation of the ice sheet surface from aircraft now provide a much better picture of the whether the ice sheet is graining or losing mass. However, until there is a better understanding of how ice flows from the ice sheet interior to the ocean, models that aim to predict the response of the Greenland Ice Sheet to climate change and the impact on sea level are unlikely to produce accurate estimates. One of the least poorly understood aspects of ice flow is how meltwater lubrication at the ice sheet sole might affect the rate of ice discharge to the ocean. Recent research has shown that the input of surface meltwater to the ice sheet bed in summer causes considerable ice speed up. Exactly how meltwater flows at the bed (does it flow in discrete channels or does it spread out and flow in a more diffuse manner?) is crucial to understanding how the ice sheet might respond to increased melt inputs in a warming climate. Currently, little is known about basal meltwater routing because the vast amounts of meltwater prevent the use of traditional tracing techniques (e.g. dye tracing). This project aims to apply novel tracing methods which will survive large scale dilution, and which can be injected to holes (moulins) on the glacier surface and detected when the water emerges at the ice sheet front. Some of these techniques have been using widely in oceanography to trace currents across ocean basins. Our tracer experiments will provide new information regarding characteristics of meltwater flow paths and their temporal/spatial variations at the bed of the ice sheet and provide detailed measurements (e.g. pressure) of along-flow path characteristics. Comparison of our tracer results (e.g. water flow speeds, pressure conditions in channels) with ice velocity data from the same glacier will help identify linkages between meltwater routing and ice flow mechanisms, and will generate a unique dataset for future numerical modelling studies aimed at quantifying the future contribution of the Greenland Ice Sheet to global sea level rise.level rise.