The Dynamics of Marine Ice Sheets
The Dynamics of Marine Ice Sheets
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DOI：
10.3189/s0022143000014726
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发表时间：
1979
影响因子：
3.4
通讯作者：
R. Thomas
中科院分区：
文献类型：
--
作者：
R. Thomas
海洋冰盖位于大部分低于海平面的陆地上。在冰原漂浮的地方，流过接地线的冰，要么变成冰山，要么形成与冰原相连的漂浮冰架。在接地线处存在冰盖动力向冰架动力的转变，该区域的蠕变变薄速率对海洋深度非常敏感；海平面上升导致冰层变薄率增加和基准线后退，而海平面下降则产生相反的效果。如果基岩向冰架中心倾斜，可能只有两种稳定模式：自由漂浮的冰架或延伸到大陆架边缘的海洋冰架。一旦开始，这种冰盖崩塌形成冰架的过程可能会非常迅速。在海洋冰盖的港湾中形成的冰架或部分接地的冰架具有稳定的影响，因为流过接地线的冰必须将冰架推过其两侧。接地线的后退往往会扩大冰架，最终可能变得足够大，以防止过度流出冰盖，从而建立新的平衡接地线；冰架的移除将使退缩得以继续。在威斯康辛州晚期冰川高峰时期，北半球可能有海洋冰盖，但目前唯一的例子是南极西部冰盖。这是由罗斯和罗恩冰架支撑的，如果气候变暖阻止了这些冰架的存在，那么冰盖就会崩溃。实地观察表明，目前冰盖可能正在向罗斯冰架的部分地区推进。然而，这样的推进并不能保证冰盖的安全，因为流向北方的冰流似乎直接流入海洋，几乎没有冰架支撑它们。如果这些冰流没有流过足够高的基岩，那么它们很可能为冰盖的退缩提供了途径。
Abstract Marine ice sheets rest on land that, for the most part, is below sea-level. Ice that flows across the grounding line, where the ice sheet becomes afloat, either calves into icebergs or forms a floating ice shelf joined to the ice sheet. At the grounding line there is a transition from ice-sheet dynamics to ice-shelf dynamics, and the creep-thinning rate in this region is very sensitive to sea depth; rising sea-level causes increased thinning-rates and grounding-line retreat, falling sea-level has the reverse effect. If the bedrock slopes down towards the centre of the ice sheet there may be only two stable modes: a freely-floating ice shelf or a marine ice sheet that extends to the edge of the continental shelf. Once started, collapse of such an ice sheet to form an ice shelf may take place extremely rapidly. Ice shelves which form in embayments of a marine ice sheet, or which are partially grounded, have a stabilizing influence since ice flowing across the grounding line has to push the ice shelf past its sides. Retreat of the grounding line tends to enlarge the ice shelf, which ultimately may become large enough to prevent excessive outflow from the ice sheet so that a new equilibrium grounding line is established; removal of the ice shelf would allow retreat to continue. During the late-Wisconsin glacial maximum there may have been marine ice sheets in the northern hemisphere but the only current example is the West Antarctic ice sheet. This is buttressed by the Ross and Ronne Ice Shelves, and if climatic warming were to prohibit the existence of these ice shelves then the ice sheet would collapse. Field observations suggest that, at present, the ice sheet may be advancing into parts of the Ross Ice Shelf. Such advance, however, would not ensure the security of the ice sheet since ice streams that drain to the north appear to flow directly into the sea with little or no ice shelf to buttress them. If these ice streams do not flow over a sufficiently high bedrock sill then they provide the most likely avenues for ice-sheet retreat.