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(GRI)正在缩小。事实上，到2100年，从冰盖流出的融化水预计将对全球海平面贡献约10厘米(Fettweis等人，2013年)。这将使目前遭受洪灾的人数翻一番(Nicholls，2006)，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，并且可能含有溶解的营养物质，高融水流向海洋的流量可能会对海洋循环(Luo等人，2016)和沿海/峡湾生态系统(例如，Hawking等人，2015)产生影响。除了这些直接影响之外，在其出海的过程中，融水径流还牵涉到一系列过程，这些过程也有助于冰的流失(称为反馈)。重要的是，这包括流经冰盖下的表面融化水，在那里它可以润滑冰流(Schoof 2010)。这表明，气候变暖导致的融化增加可能会导致冰盖持续加速，导致冰盖变薄和变平。这会给气温较高的地区带来更多的冰，从而加剧融化，有可能导致更多的质量损失。目前尚不清楚这是否会因为涉及的复杂过程而发生(例如，Tedstone等人，2015)，但我们的研究表明，未来可能会有更多的亚冰盖环境暴露在这些过程中(Leeson等人，2015)。因此，增进我们对该系统及其运作方式的理解是非常重要的。目前，未来的全球海平面变化(例如，政府间气候变化专门委员会-气专委评估报告中的海平面贡献估计)是使用冰盖模型来预测的，该模型没有完全考虑到上述反馈过程。地表融化对冰流的影响受地表和基本水文特征的控制，例如湖泊和溪流。对于冰盖模型来说，这些特征太小，变化太快，这就是为什么到目前为止它们还没有被包括在这些模型中的原因。然而，我们的项目组最近率先取得的技术进步(例如Goldberg等人，2009年和Gourmelen等人，2017年)现在允许冰盖模型模拟小规模和大型过程，最先进的卫星现在捕获了足够的信息，使我们能够全面评估这样的模型。在这个项目中，我们将利用这些进展，开发一种新的、健壮的、耦合的水文/冰盖模型，该模型完全受约束，并根据新的和专门的观测进行测试。然后，我们将使用该模型来1)提高我们对地表融水在冰动力学中的作用的理解，以及2)模拟GRIS对IPCC气候变暖情景下预期的地表融化变化的响应。

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.