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

海洋终止冰川前缘的退缩通常与冰流加速、冰山崩解率增加和向海洋的排放以及冰川变薄有关。相关的冰量损失是导致格陵兰冰盖在本世纪迄今为止对海平面上升贡献的大约一半。在世纪的剩余时间里，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的不确定性。这一合作项目旨在揭示格陵兰海洋终止冰川不同环境中控制终止退缩和冰山崩解的因素。该项目通过为来自EPSCoR州的两名早期职业科学家提供支持，两所大学的本科生参与以及研究生的培训，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，向非技术团体进行演讲，以及媒体专题报道。该项目将通过分析最近可用的观测数据集，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点参数化的性能，即所谓的“产犊定律”。“在格陵兰岛周围49个不同的海洋终止冰川（近冰盖总数的四分之一）的应用确保了项目结果具有代表性。适用于冰川终点及其附近条件的裂冰定律将预测终点位置。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点位置和产犊率。此外，这种方法的扩展将（1）深入了解冰隙水储存对冰山产犊的影响，（2）指导包括海底融化，以改善产犊规律的预测，（3）量化关键的时间尺度，在此时间尺度上，冰川特性必须被表征，以预测产犊率和终点位置。

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.