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

格陵兰冰盖是北方的主要冰库，能够影响世纪的海平面。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在颗粒化还是在失去质量。然而，在更好地了解冰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以及对海平面的影响的模型不太可能产生准确的估计。对冰流了解最少的一个方面是冰盖底部的融水润滑作用如何影响冰向海洋排放的速度。最近的研究表明，在夏季输入的表面融水的冰盖床造成相当大的冰的速度。融水到底是如何在河床上流动的（它是在离散的通道中流动，还是以更扩散的方式扩散和流动？）对于了解冰盖如何应对气候变暖中增加的融化输入至关重要。目前，很少有人知道的基础融水路由，因为大量的融水阻止使用传统的跟踪技术（如染料跟踪）。该项目旨在应用新的追踪方法，这些方法将在大规模稀释中幸存下来，并且可以注入冰川表面上的洞（冰臼），并在水出现在冰盖前沿时进行检测。这些技术中的一些已被广泛用于海洋学追踪跨海洋盆地的电流。我们的示踪剂实验将提供新的信息，关于融水流动路径的特性及其在冰盖床的时间/空间变化，并提供详细的测量（如压力）沿流路径特性。我们的示踪结果（例如水流速度，通道中的压力条件）与来自同一冰川的冰速度数据的比较将有助于确定融水路由和冰流机制之间的联系，并将为未来的数值模拟研究生成一个独特的数据集，旨在量化格陵兰冰盖对全球海平面上升的未来贡献。

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.