Collaborative Research: What Controls Calving? A Greenland-wide Test of Terminus Change Mechanisms

海洋冰川前缘的退缩通常与冰流加速、冰山崩解速度和向海洋排放的增加以及冰川变薄有关。本世纪到目前为止，格陵兰冰盖对海平面上升的贡献大约有一半是由相关的冰块质量损失造成的。在本世纪余下的时间和以后，我们对冰山崩解和冰川退缩的理解存在差距，导致对质量损失和随之而来的海平面上升的预测存在很大不确定性。这一合作项目旨在揭示在格陵兰海洋冰川的不同环境中控制冰川末端消退和冰山崩解的因素。该项目通过支持两名来自EPSCoR州的早期职业科学家、两所大学的本科生参与以及一名研究生的培训，为STEM劳动力发展做出了贡献。主要研究人员将继续积极开展活动，包括在大学周围的农村地区参观博物馆和教室，向非技术小组介绍情况，以及媒体专题报道。该项目将通过分析最近获得的观测数据集，极大地提高我们对海洋冰川终止动力学的理解。通过这些数据，该项目将评估在数值冰盖模型中使用的终端参数化的性能，即所谓的“崩解定律”。在格陵兰岛周围49个不同的海洋终止冰川(几乎占冰盖总数的四分之一)上的应用确保了项目成果的代表性。冰川终点处及其附近条件适用的崩解定律将预测冰川终点处的位置。预测将与卫星和延时图像中观察到的终点位置进行比较，以确定模型不匹配。这种校准和验证分析将揭示特定的产犊规律何时何地可靠地再现终点位置和产奶率。此外，这一方法的推广将：(1)洞察裂隙水储存对冰山崩解的影响，(2)指导包括海底融化，以通过崩解规律改进预测，以及(3)量化冰川特性的关键时间尺度，以预测冰川崩解速度和终点位置。

Retreat of the leading edge of marine-terminating glaciers is often associated with ice flow acceleration, increases in iceberg calving rates and discharge to the sea, and glacier thinning. The associated ice mass loss is responsible for approximately half the contribution of the Greenland Ice Sheet to sea level rise thus far this century. For the remainder of the century and beyond, gaps in our understanding of iceberg calving and glacier retreat result in large uncertainties in predictions of mass loss and consequent sea level rise. This collaborative project is designed to reveal the factors controlling terminus retreat and iceberg calving in the diverse settings of Greenland's marine terminating glaciers. The project contributes to STEM workforce development by providing support to two early-career scientists from EPSCoR states, undergraduate student participation at both institutions, and for training of a graduate student. The principal investigators will continue their active outreach, including museum and classroom visits in the rural settings around their universities, presentations to non-technical groups, and media features.This project will substantially improve our understanding of marine terminating glacier dynamics via the analysis of recently-available observational datasets. Through these data, the project will evaluate the performance of terminus parameterizations used in numerical ice sheet models, known as "calving laws." Application at 49 diverse marine-terminating glaciers around Greenland (nearly a quarter of the ice sheet total) ensures that project results will be representative. Calving laws applied to conditions at and near glacier termini will predict terminus locations. Predictions will be compared to terminus positions observed in satellite and time-lapse images to identify model misfits. This calibration and validation analysis will reveal when and where specific calving laws reliably reproduce terminus positions and calving rates. Furthermore, extensions of this approach will (1) yield insight into the impact of crevasse water storage on iceberg calving, (2) guide the inclusion of submarine melting to improve prediction by calving laws, and (3) quantify the critical timescales over which glacier properties must be characterized for the prediction of calving rates and terminus positions.