Meltwater Ice-sheet Interactions and the changing climate of Greenland (MII-Greenland)

随着地球气候变暖，格陵兰冰盖（GrIS）正在缩小。事实上，预计到2100年，从冰盖上流下的融水将使全球海平面上升约10厘米（Fettweis等人，2013年）。这将使目前遭受洪水的人数增加一倍（Nicholls，2006年），可能导致全世界的生命和生计损失。此外，由于融水是新鲜的，而不是咸的，并且可以含有溶解的营养物质，因此流向海洋的高融水通量可能对海洋环流产生影响（Luo等人，2016年）和沿海/峡湾生态系统（如Hawkings等人，2015年）。除了这些直接影响外，在其出海的过程中，融水径流还涉及一系列过程，这些过程也有助于冰的损失（称为反馈）。重要的是，这包括在冰盖下流动的表面融水，在那里它可以润滑冰流（Schoof 2010）。这表明，由于气候变暖导致的融化增加可能导致冰盖持续加速，导致变薄和变平。这将加剧融化，因为更多的冰将被带到气温较高的海拔地区，可能导致更多的质量损失。由于所涉及的复杂过程，尚不清楚这是否会发生（例如Tedstone等人，2015年），然而，我们的研究表明，未来更多的亚冰盖环境可能会暴露于这些过程（Leeson等人，2015年）。因此，提高我们对该系统及其功能的理解是非常重要的。目前，未来的GrIS变化（例如，政府间气候变化专门委员会（IPCC）评估报告中的海平面贡献估计）是使用冰盖模型预测的，这些模型没有充分考虑上述反馈过程。地表融化对冰流的影响受地表和基底水文特征（如湖泊和溪流）的控制。这些特征太小，而且发展得太快，冰盖模型无法模拟，这就是为什么它们直到现在才被包括在这些模型中。我们的项目团队开创的最新技术进步（例如Goldberg等人，2009和Gourmelen等人，然而，现在允许冰盖模型模拟小规模和大规模的过程，最先进的卫星现在捕获足够的信息，让我们充分评估这样的模型。在这个项目中，我们将利用这些进步，并开发一个新的，强大的，耦合水文/冰盖模型，这是彻底约束和测试对新的，专用的，观测。然后，我们将使用该模型来1）提高我们对冰动力学中表面融水作用的理解，2）模拟GrIS对IPCC气候变暖情景下预期的表面融化变化的响应。

The Greenland ice sheet (GrIS) is shrinking as Earth's climate warms. In fact, meltwater which runs off the ice sheet is expected to contribute ~10 cm to global sea level by 2100 (Fettweis et al., 2013). This would double the number of people currently experiencing flooding (Nicholls, 2006) potentially cuasing the loss of lives and livelihoods worldwide. Additionally, because meltwater is fresh as opposed to salty, and can contain dissolved nutrients, high meltwater fluxes to the ocean can potentially have an impact on ocean circulation (Luo et al., 2016) and coastal/fjord ecosystems (e.g. Hawkings et al., 2015). In addition to these direct impacts, on its journey out to sea, the meltwater runoff is implicated in a range of processes which also contribute to ice loss (known as feedbacks). Importantly, this includes surface meltwater which is routed underneath the ice sheet, where it can lubricate ice flow (Schoof 2010). This suggests that increases in melt due to a warming climate could lead to a sustained speed-up of the ice sheet; leading to a thinning and flattening. This would exacerbate melting by bringing more ice to elevations with warmer air temperatures, potentially resulting in more mass loss. It is not yet clear whether this will occur because of the complicated processes involved (e.g. Tedstone et al., 2015), however our research has that shown more of the sub-ice sheet environment is likely to be exposed to these processes in the future (Leeson et al., 2015). As such, improving our understanding of the system and how it functions is of great importance.At present, future GrIS change (e.g. estimates of sea level contribution which feature in the Intergovernmental Panel on Climate Change - IPCC - assessment reports) is predicted using ice sheet models which do not fully account for the feedback processes outlined above. The impact of surface melting on ice flow is controlled by surface and basal hydrological features, for example lakes and streams. These features are too small, and evolve too quickly, for the ice sheet models to simulate, which is why they have not been included in these models until now. Recent technological advances pioneered by our project team (e.g. Goldberg et al., 2009 and Gourmelen et al., 2017) however, now allow for ice sheet models to simulate both small and large scale processes and state-of-the art satellites now capture enough information for us to fully evaluate such a model. In this project we will exploit these advances and develop a new, robust, coupled hydrology/ice-sheet model which is thoroughly constrained and tested against new, and dedicated, observations. We will then use the model to 1) improve our understanding of the role of surface meltwater in ice dynamics and 2) simulate the GrIS response to changes in surface melting expected under IPCC climate warming scenarios.