A Thin Film Viscoplastic Theory for Calving Glaciers: Toward a Bound on the Calving Rate of Glaciers
A Thin Film Viscoplastic Theory for Calving Glaciers: Toward a Bound on the Calving Rate of Glaciers
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DOI：
10.1029/2019jf005160
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发表时间：
2019-08-01
影响因子：
3.9
通讯作者：
Ultee, L.
中科院分区：
文献类型：
--
作者：
Bassis, J. N.;Ultee, L.
预估冰原和冰川的生长和消亡需要控制冰的流动和断裂过程的物理模型。冰川冰的流动已经被越来越复杂的模型所处理。相比之下，由于冰山崩解，最终造成一半冰盖质量损失的断裂过程，通常使用特别的参数化来计算。在这项研究中，我们试图通过引入一个模型来弥合这一差距，在这个模型中，冰服从幂律流变学，适用于低于屈服强度的完整冰。在屈服强度之上，我们引入了一种单独的流变学，适用于严重断裂的冰的流动，在这种情况下，冰的变形更容易沿着断层和裂缝发生。我们表明，如果断裂冰的运动比完整冰的运动足够快，冰川的行为完全取决于完整冰的流变学和冰的屈服强度，而对断裂冰的精确流变学不敏感。此外，假设冰川未消融，我们可以限定冰川末端移动的长期平均速率，从而提供与海洋冰崖不稳定性相关的退缩速率的基本估计。我们使用理想化的几何形状和气候强迫来说明模式行为，并表明该模式不仅表现出前进和后退的现实模式，而且还具有表现出滞后的潜力。这种滞后性可以解释在海洋终止的冰川中观察到的快速退缩的突然发生。
Projections of the growth and demise of ice sheets and glaciers require physical models of the processes governing flow and fracture of ice. The flow of glacier ice has been treated using increasingly sophisticated models. By contrast, fracture, the process ultimately responsible for half of the mass lost from ice sheets through iceberg calving, is often included using ad hoc parameterizations. In this study we seek to bridge this gap by introducing a model where ice obeys a power law rheology appropriate for intact ice below a yield strength. Above the yield strength, we introduce a separate rheology appropriate for the flow of heavily fractured ice, where ice deformation occurs more readily along faults and fractures. We show that, provided the motion of fractured ice is sufficiently rapid compared to that of intact ice, the behavior of glaciers depends solely on the rheology of intact ice and the yield strength of ice and is insensitive to the precise rheology of fractured ice. Moreover, assuming that glacier ice is unyielded allows us to bound the long-term average rate of terminus advance, providing a first principles estimate of rates of retreat associated with the marine ice cliff instability. We illustrate model behavior using idealized geometries and climate forcing and show that the model not only exhibits realistic patterns of advance and retreat but also has the potential to exhibit hysteresis. This hysteresis could provide an explanation for the sudden onset of rapid retreat observed in marine-terminating glaciers.