Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109.
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109;
Proc Natl Acad Sci U S A. 2021 Oct 5;118(40). doi: 10.1073/pnas.2105080118.
The sudden propagation of a major preexisting rift (full-thickness crack) in late 2016 on the Larsen C Ice Shelf, Antarctica led to the calving of tabular iceberg A68 in July 2017, one of the largest icebergs on record, posing a threat for the stability of the remaining ice shelf. As with other ice shelves, the physical processes that led to the activation of the A68 rift and controlled its propagation have not been elucidated. Here, we model the response of the ice shelf stress balance to ice shelf thinning and thinning of the ice mélange encased in and around preexisting rifts. We find that ice shelf thinning does not reactivate the rifts, but heals them. In contrast, thinning of the mélange controls the opening rate of the rift, with an above-linear dependence on thinning. The simulations indicate that thinning of the ice mélange by 10 to 20 m is sufficient to reactivate the rifts and trigger a major calving event, thereby establishing a link between climate forcing and ice shelf retreat that has not been included in ice sheet models. Rift activation could initiate ice shelf retreat decades prior to hydrofracture caused by water ponding at the ice shelf surface.
2016 年末，南极洲拉森 C 冰架上一条先前存在的大裂隙（全厚度裂缝）突然扩张，导致 2017 年 7 月形成了 A68 平板冰山，这是有记录以来最大的冰山之一，对剩余冰架的稳定性构成了威胁。与其他冰架一样，导致 A68 裂隙激活并控制其扩展的物理过程尚未阐明。在这里，我们模拟了冰架应力平衡对冰架变薄和包裹在先前裂隙内及周围的冰混杂物变薄的响应。我们发现，冰架变薄不会重新激活裂隙，反而会使其愈合。相比之下，冰混杂物的变薄控制着裂隙的张开率，与变薄呈超线性关系。模拟表明，冰混杂物变薄 10 到 20 米足以重新激活裂隙并引发大规模崩解事件，从而在冰盖模型中建立了气候强迫与冰架退缩之间的联系，而这一联系此前并未被包括在内。裂隙的激活可能会导致冰架退缩，比因冰架表面积水而导致的水压断裂提前几十年。
