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

终结海洋的冰川前缘的退缩通常与冰流加速、冰山崩解速率和向海洋排放的增加以及冰川变薄有关。本世纪迄今为止，格陵兰冰盖对海平面上升的贡献中，约有一半是由相关的冰质量损失造成的。在本世纪余下的时间里及以后，我们对冰山崩解和冰川退缩的理解存在差距，导致对冰川质量损失和随之而来的海平面上升的预测存在很大的不确定性。这个合作项目的目的是揭示控制终端退缩和冰山崩解的因素在格陵兰岛的海洋终端冰川的不同设置。该项目通过为来自EPSCoR州的两名早期职业科学家、两所大学的本科生参与以及一名研究生的培训提供支持，促进了STEM劳动力的发展。主要研究人员将继续积极开展外联活动，包括在大学周围的农村环境中参观博物馆和教室，向非技术团体进行介绍，并进行媒体专题报道。该项目将通过对最近可获得的观测数据集的分析，大大提高我们对海洋终止冰川动力学的理解。通过这些数据，该项目将评估用于数值冰盖模型的终端参数化的性能，即所谓的“冰解定律”。在格陵兰岛周围49个不同的海洋终止冰川（近四分之一的冰盖总数）的应用确保了项目结果的代表性。适用于冰川终点站及其附近条件的产犊定律将预测终点站的位置。预测结果将与卫星和延时图像中观测到的终端位置进行比较，以确定模型的不匹配。这种校准和验证分析将揭示何时何地特定的产犊规律可靠地再现终端位置和产犊率。此外，该方法的扩展将(1)深入了解裂缝储水量对冰山崩解的影响，(2)指导将海底融化纳入其中，以改进通过崩解规律进行的预测，以及(3)量化预测崩解速率和终点位置必须表征冰川特性的关键时间尺度。

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.