NSFGEO-NERC: Investigating the Direct Influence of Meltwater on Antarctic Ice Sheet Dynamics

当冰盖和冰川失去冰的速度比降雪积累的速度快时，它们就会收缩，导致海平面上升。这对地球仪各地的沿海社区产生了影响，例如，增加了破坏性风暴潮的频率。海平面上升已经在进行中，地球科学界面临的一个主要挑战是改善对海平面上升将如何演变的预测。南极冰盖是海平面上升的最大潜在因素，其未来非常不确定。它通过两个主要机制失去冰：冰山的形成和其外围浮动冰架底部的融化。冰在重力作用下流向海洋，冰流的速度控制着冰盖和冰川收缩的速度。在格陵兰岛和南极洲，冰流集中在出口冰川和冰流中，它们的流动速度比周围地区快得多。此外，格陵兰冰盖的部分地区在每小时到季节的时间尺度上大幅加速和减速，特别是在地表融水到达冰层底部的地方。到达冰底的融水改变了冰的流动，改变了冰底的水压力，从而改变了冰下岩石和沉积物对冰的摩擦力。这种现象在格陵兰经常观察到，但在南极洲却没有。最近的卫星观测表明，这种现象也发生在南极半岛的出口冰川上。由于预计本世纪南极洲周围的气温和表面融化将增加，到达南极冰盖底部的融水可能会变得更加普遍。该项目的目的是确认最近的卫星观测，建立一个基线，以比较未来的变化，并提高对融水对南极冰盖动态的直接影响的理解。 这是一个由国家科学基金会地球科学理事会（NSF/GEO）和联合王国国家环境研究理事会（NERC）通过NSF/GEO-NERC牵头机构协议联合资助的项目。该协议允许美国/英国提交一份联合提案，并由研究者拥有最大预算比例的机构进行同行评审。在成功地共同确定奖励建议后，每个机构将资助其各自国家研究机构科学家的预算部分，该项目将包括在弗拉斯克冰川、南极半岛出口冰川上开展实地活动，并进行全大陆遥感调查。这些活动将使研究小组能够检验与南极冰盖对表面融水的动态响应有关的三个假设：（1）卫星数据显示的冰速度的短期变化是表面融水到达冰床的结果，（2）这在今天的南极洲很普遍，（3）这导致平均年冰流量的可测量增加。该项目是美国和英国研究人员之间的合作，将得到英国南极调查局的后勤支持。该项目旨在深入了解由表面融化引起的冰流速短期变化的驱动因素和影响。例如，如果能确凿地证明融水直接影响南极冰的动态，将对理解南极洲对大气变暖的反应产生重大影响，就像20年前在格陵兰岛首次发现这一现象时所做的那样。这项工作也可能影响其他领域，因为到达南极冰盖床的表面融水可能会影响冰流变学，冰下水文学，海底融化，崩解，海洋环流和海洋地球化学。该项目旨在通过支持早期职业科学家、英美合作、教育和推广以及在冰川学界采用开放数据科学方法，对科学和社会产生更广泛的影响。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

When ice sheets and glaciers lose ice faster than it accumulates from snowfall, they shrink and contribute to sea-level rise. This has consequences for coastal communities around the globe by, for example, increasing the frequency of damaging storm surges. Sea-level rise is already underway and a major challenge for the geoscience community is improving predictions of how this will evolve. The Antarctic Ice Sheet is the largest potential contributor to sea-level rise and its future is highly uncertain. It loses ice through two main mechanisms: the formation of icebergs and melting at the base of floating ice shelves on its periphery. Ice flows under gravity towards the ocean and the rate of ice flow controls how fast ice sheets and glaciers shrink. In Greenland and Antarctica, ice flow is focused into outlet glaciers and ice streams, which flow much faster than surrounding areas. Moreover, parts of the Greenland Ice Sheet speed up and slow down substantially on hourly to seasonal time scales, particularly where meltwater from the surface reaches the base of the ice. Meltwater reaching the base changes ice flow by altering basal water pressure and consequently the friction exerted on the ice by the rock and sediment beneath. This phenomenon has been observed frequently in Greenland but not in Antarctica. Recent satellite observations suggest this phenomenon also occurs on outlet glaciers in the Antarctic Peninsula. Meltwater reaching the base of the Antarctic Ice Sheet is likely to become more common as air temperature and surface melting are predicted to increase around Antarctica this century. This project aims to confirm the recent satellite observations, establish a baseline against which to compare future changes, and improve understanding of the direct influence of meltwater on Antarctic Ice Sheet dynamics. This is a project jointly funded by the National Science Foundation’s Directorate for Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award recommendation, each Agency funds the proportion of the budget that supports scientists at institutions in their respective countries.This project will include a field campaign on Flask Glacier, an Antarctic Peninsula outlet glacier, and a continent-wide remote sensing survey. These activities will allow the team to test three hypotheses related to the Antarctic Ice Sheet’s dynamic response to surface meltwater: (1) short-term changes in ice velocity indicated by satellite data result from surface meltwater reaching the bed, (2) this is widespread in Antarctica today, and (3) this results in a measurable increase in mean annual ice discharge. The project is a collaboration between US- and UK-based researchers and will be supported logistically by the British Antarctic Survey. The project aims to provide insights into both the drivers and implications of short-term changes in ice flow velocity caused by surface melting. For example, showing conclusively that meltwater directly influences Antarctic ice dynamics would have significant implications for understanding the response of Antarctica to atmospheric warming, as it did in Greenland when the phenomenon was first detected there twenty years ago. This work will also potentially influence other fields, as surface meltwater reaching the bed of the Antarctic Ice Sheet may affect ice rheology, subglacial hydrology, submarine melting, calving, ocean circulation, and ocean biogeochemistry. The project aims to have broader impacts on science and society by supporting early-career scientists, UK-US collaboration, education and outreach, and adoption of open data science approaches within the glaciological community.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.