The Effect of Meltwater Plumes on the Melting of a Vertical Glacier Face
The Effect of Meltwater Plumes on the Melting of a Vertical Glacier Face
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DOI：
10.1175/jpo-d-13-0219.1
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发表时间：
2014-12-01
影响因子：
3.5
通讯作者：
Piggott, Matthew
中科院分区：
文献类型：
--
作者：
Kimura, Satoshi;Holland, Paul R.;Piggott, Matthew
冰原表面融化产生的淡水通常从深峡湾末端冰川的底部排入海洋峡湾。淡水的排放在冰川断裂面前形成上涌羽流。本研究使用非流体静力学海洋模型模拟了融水羽流喷入未分层环境的情况，该模型采用非结构化网格和子网格尺度混合，并与已建立的羽流理论进行了比较校准。冰面的存在减少了海水对融水羽流的夹带，因此羽流仍附着在冰面上，这与以前的简单模型不同。作者推测，这种 "过度切割 "可能是冰山在开裂时向冰面内倾的趋势的原因。研究发现，总体熔化率随排水通量的增加而增加，但只达到一个临界值，而这个临界值取决于通道的大小。熔化率并不是冰川下泄流量的简单函数，这一点在之前的许多研究中都有所假设。在给定的排泄流量下，羽流源的几何形状也会对熔化产生重大影响，较薄、较宽的羽流源会获得较高的熔化率。在较宽的通道中，源附近会产生两个羽流，这些羽流最终会聚合在一起。这种合并的融水羽流上升速度更快，增加了通道中心附近的最大熔化率。
Freshwater produced by the surface melting of ice sheets is commonly discharged into ocean fjords from the bottom of deep fjord-terminating glaciers. The discharge of the freshwater forms upwelling plumes in front of the glacier calving face. This study simulates the meltwater plumes emanated into an unstratified environment using a nonhydrostatic ocean model with an unstructured mesh and subgrid-scale mixing calibrated by comparison to established plume theory. The presence of an ice face reduces the entrainment of seawater into the meltwater plumes, so the plumes remain attached to the ice front, in contrast to previous simple models. Ice melting increases with height above the discharge, also in contrast to some simple models, and the authors speculate that this "overcutting" may contribute to the tendency of icebergs to topple inwards toward the ice face upon calving. The overall melt rate is found to increase with discharge flux only up to a critical value, which depends on the channel size. The melt rate is not a simple function of the subglacial discharge flux, as assumed by many previous studies. For a given discharge flux, the geometry of the plume source also significantly affects the melting, with higher melt rates obtained for a thinner, wider source. In a wider channel, two plumes are emanated near the source and these plumes eventually coalesce. Such merged meltwater plumes ascend faster and increase the maximum melt rate near the center of the channel The melt rate per unit discharge decreases as the subglacial system becomes more channelized.