Modeling ice-ocean interaction in ice-shelf crevasses
Modeling ice-ocean interaction in ice-shelf crevasses
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DOI：
10.1002/2013jc009208
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发表时间：
2014-02-01
影响因子：
3.6
通讯作者：
Kimura, Satoshi
中科院分区：
文献类型：
--
作者：
Jordan, James R.;Holland, Paul R.;Kimura, Satoshi
冰架基底裂缝内的海洋结冰可能对冰架产生稳定影响；然而，人们对这些裂缝内的冰海相互作用和海洋动力学仍然知之甚少。为此，我们使用 Fluidity（一种使用非结构化网格的有限元海洋模型）开发了冰架基底裂缝的理想化二维模型。 Fluidity 中已纳入冰晶形成和沉积的简单模型，以更好地表示冻结过程。模型结果显示了两种不同的流动状态，具体取决于裂缝中的冻结量：一种是由裂缝顶部的冻结驱动的，另一种是由裂缝外部融水的进入驱动的。第一种情况是，裂缝顶部结冰，由于排斥浓密的咸水，导致形成不稳定的翻转循环。在第二种情况下，沿着裂缝的侧面和顶部形成浮力层，使水柱分层。研究发现，在冻结驱动的情况下，冰降水是基底裂隙顶部的主要冻结过程，而在融化驱动的情况下，直接冻结是主要的。在这两种情况下，由于强烈的翻转循环，融化发生在裂缝壁的下方。研究发现，冰架裂缝和裂缝中的冻结高度依赖于海洋温度，这对其他地方不存在的冷水下方的冰架产生了稳定影响。
Ocean freezing within ice-shelf basal crevasses could potentially act as a stabilizing influence on ice shelves; however, ice-ocean interaction and ocean dynamics within these crevasses are as yet poorly understood. To this end, an idealized 2-D model of an ice-shelf basal crevasse has been developed using Fluidity, a finite-element ocean model using an unstructured mesh. A simple model of frazil ice formation and deposition has been incorporated into Fluidity to better represent the freezing process. Model results show two different flow regimes, dependent on the amount of freezing in the crevasse: one driven by freezing at the top of the crevasse and the other by the ingress of meltwater from outside the crevasse. In the first, freezing at the top of the crevasse leads to the formation of an unstable overturning circulation due to the rejection of dense, salty water. In the second, a buoyant layer is formed along the sides and roof of the crevasse, stratifying the water column. Frazil ice precipitation is found to be the dominant freezing process at the top of the basal crevasse in the freeze-driven case, with direct freezing being dominant in the melt-driven case. In both cases, melting occurs lower down on the walls of the crevasse due to the strong overturning circulation. The freezing in ice-shelf crevasses and rifts is found to be highly dependent upon ocean temperature, providing a stabilizing influence on ice shelves underlain by cold waters that is not present elsewhere.