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

当冰盖和冰川融化的速度快于降雪积累的速度时，它们就会收缩，并导致海平面上升。这对全球沿海社区产生了影响，例如，增加了破坏性风暴潮的频率。海平面已经在上升，地球科学界面临的一大挑战是改进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贡献者，其未来非常不确定。它通过两种主要机制失去冰：冰山的形成和外围漂浮冰架底部的融化。冰在重力作用下流向海洋，冰流的速度控制着冰盖和冰川缩小的速度。在格陵兰岛和南极洲，冰流集中在出口冰川和冰流中，这些冰川和冰流的流动速度比周围地区快得多。此外，格陵兰冰盖的部分在每小时到季节性的时间尺度上加速和减速，特别是在表面融化的水到达冰层底部的地方。到达底部的融水通过改变基本水压来改变冰流，从而改变下面岩石和沉积物施加在冰上的摩擦力。这种现象在格陵兰岛经常观察到，但在南极洲并不常见。最近的卫星观测表明，这种现象也出现在南极半岛的出口冰川上。到达南极冰盖底部的融水可能会变得更加常见，因为预计本世纪南极洲周围的气温和表面融化将会增加。该项目旨在确认最近的卫星观测，建立比较未来变化的基线，并增进对融水对南极冰盖动态的直接影响的了解。这是一个由国家科学基金会地球科学局(NSF/GEO)和英国国家环境研究委员会(NERC)通过NSF/GEO-NERC牵头机构协议共同资助的项目。该协定允许美国和英国提交一个单一的联合提案，并由该机构进行同行审查，该机构的调查员在预算中所占比例最大。在成功地联合确定一项奖项建议后，每个机构将资助其各自国家机构中支持科学家的预算比例。该项目将包括关于长颈瓶冰川、南极半岛出口冰川的实地活动，以及一项全大陆的遥感调查。这些活动将使该小组能够测试与南极冰盖对表面融化水的动态响应有关的三个假说：(1)卫星数据显示的冰速的短期变化是表面融化水到达海床的结果，(2)这在今天的南极洲很普遍，(3)这导致平均年冰流量显著增加。该项目是美国和英国研究人员的合作项目，将得到英国南极调查局的后勤支持。该项目旨在提供对表面融化导致的冰流速度短期变化的驱动因素和影响的见解。例如，得出结论，表明融化的水直接影响南极的冰动态，这将对理解南极洲对大气变暖的反应具有重要意义，就像20年前格陵兰岛首次发现这种现象时一样。这项工作还可能影响其他领域，因为到达南极冰盖底部的表面融化水可能会影响冰的流变学、冰下水文、海底融化、崩解、海洋环流和海洋生物地球化学。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智力优势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.