Greenland in a warmer climate: What controls the advance & retreat of the NE Greenland Ice Stream

在过去的十年里，格陵兰冰盖正在加速变薄，目前是全球海平面上升的最大单一因素。了解未来变化的可能速度和幅度很重要，因为如果各国政府要为全球变暖的未来做规划，并制定可持续的海岸防御战略，就必须对海平面上升进行准确的预测。格陵兰岛对海平面上升的很大一部分贡献与越来越多的快速流动的出海口冰川的加速和融化有关。这些冰川的迅速变薄与空气和海洋温度的升高同时发生，这表明它们对这些参数很敏感，也很敏感。然而，尽管已经提出了与大气和海洋强迫有关的各种机制来解释最近的变薄，但在较长时间尺度上，每种机制与冰盖对它们的响应之间的相对重要性和相互作用存在很大的不确定性。如果没有这一关键信息，当前这一代冰盖模式的产出就有局限性，而且海平面上升预测可能出现重大误差。这项研究将通过重建东北格陵兰冰流（NEGIS）在过去1万年中的行为，直接解决我们理解中的这一关键差距。NEGIS特别令人感兴趣，因为最近的研究表明，在25年的相对稳定之后，这个寒冷的北极高纬度地区的冰盖开始持续变薄。这引起了人们的担忧，即迅速向内陆撤退已经开始，并可能导致NEGIS集水区的减少。其流域的完全崩塌将使海平面上升约1.4米（相当于南极洲松岛-思韦茨集水区的总和），对沿海地区的人口构成重大威胁。NEGIS为研究冰流对过去变化（海洋和大气变暖）的响应提供了一个无与伦比的机会，因为有证据表明，它在全新世热极大期（类似于预测的21世纪后期气温升高的时期）经历了戏剧性的退缩（然后前进）。为了实现这一目标，我们组建了一个经验丰富的团队，他们将生成NEGIS几何变化的详细记录，以及同期大气、海洋和相对海平面的变化。我们将根据海洋和陆地数据重建冰流结构（厚度、范围），并生成海洋和大气温度以及相对海平面的高分辨率记录。利用最先进的冰盖模型（BISICLES），这些数据将用于测试冰流在100-1000年时间尺度上对不同强迫机制的敏感性。我们选择的时间尺度将使我们能够区分短期“噪音”和长期趋势，这已被认为是一个潜在的问题，这是不可能的，从几十年的仪器记录中得出的当代边际波动的调查。最终，我们的项目将大大提高我们对冰盖对各种强迫机制的敏感性的理解，这将有助于支持海平面上升预测，制定海岸防御政策并保护子孙后代。该项目具有重要的附加价值，因为我们将在一个资助的欧洲项目“格陵兰冰盖/海洋相互作用和弗拉姆海峡通量”中开展工作，并已确认通过德国阿尔弗雷德·韦格纳研究所提供资金后勤支持，并乘坐RV北极星号（2016）前往这个偏远地区进行为期50天的巡游。

Over the past decade the Greenland ice sheet has thinned at an accelerating rate and is currently the largest single contributor to global sea-level rise. Understanding the likely rate and magnitude of future change matters because accurate projections of sea-level rise are necessary if governments are to plan for the future in a warming world and develop sustainable coastal defence strategies.A significant portion of Greenland's contribution to sea-level rise has been associated with the speed-up and melting of an increased number of fast-flowing outlet glaciers. Rapid thinning of these glaciers has coincided with increases in air and ocean temperatures, suggesting that they are sensitive and responsive to these parameters. However, although various mechanisms related to atmospheric and oceanic forcing have been proposed to explain the recent thinning, there exist large uncertainties in the relative importance of and interplay between each of these and the ice sheet response to them over longer timescales. Without this crucial information output from the current generation of ice sheet models has limitations and there is potential for significant errors in sea-level rise projections.This research will directly address this critical gap in our understanding by reconstructing the past behaviour of the Northeast Greenland Ice Stream (NEGIS) over the past 10,000 years. NEGIS is of particular interest because recent studies show that this cold, High Arctic region of the ice sheet has started to undergo sustained thinning after more than 25 years of relative stability. This has raised concerns that rapid inland retreat is already underway and could lead to drawdown of the NEGIS catchment. Complete collapse of its drainage basin would raise sea-level by ~1.4 m (equivalent to the combined Pine Island-Thwaites catchment in Antarctica) posing a major hazard for coastal populations. NEGIS provides an unparalleled opportunity to investigate the response of an ice stream to past change (oceanic and atmospheric warming), because there is evidence that it underwent dramatic retreat (and then advance) during the Holocene Thermal Maximum (a period of increased air temperatures analogous to that predicted for late 21st century). To achieve this we have assembled an experienced team who will generate a detailed record of changes in NEGIS geometry, and the contemporaneous atmospheric, oceanic and relative sea level changes. We will reconstruct ice stream configuration (thickness, extent) from marine and terrestrial data, and produce high-resolution records of oceanic and atmospheric temperatures and relative sea level. Using a state-of-the-art ice sheet model (BISICLES), these data will be used to test the sensitivity of the ice stream to different forcing mechanisms at 100-1000 year timescales. Our chosen timescale will allow us to differentiate short term 'noise' from long term trends, something that has been recognised as a potential issue, which is not possible from investigations of contemporary margin fluctuations derived from a few decades of instrumental records. Ultimately our project will deliver significant improvements in our understanding of the sensitivity of the ice sheet to various forcing mechanisms that will help to underpin sea-level rise projections, shape policy on coastal defence and protect future generations.The project has significant added value in that we will work within a funded European programme 'Greenland Ice Sheet/Ocean Interaction and Fram Strait Fluxes' and has confirmed funded logistical support through the Alfred Wegener Institute, Germany and a 50 day cruise on the RV Polarstern (2016) to this remote area.