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摘要 : 从格陵兰和南极洲冰层流出的巨大冰河在气候不断变暖的情况下是否会进入一个失控的加速状态?如果是这样,那么海平面迅速上升的最坏情景将会出现。


从格陵兰和南极洲冰层流出的巨大冰河在气候不断变暖的情况下是否会进入一个失控的加速状态?如果是这样,那么海平面迅速上升的最坏情景将会出现。Chris Stokes 及同事整理了来自在距今22,000年前和7,000年前之间发生的 “劳伦太德冰层”的消退的现有证据,显示在冰消期冰河的数量和它们的总排量都下降了。这表明,冰河活动随冰层本身的大小减小,冰河并未像人们曾经提出的那样对冰层消退的失控有贡献。然而,这些结果是“劳伦太德冰层”消退的特定结果,未必直接适用于现代的情况。


Ice stream activity scaled to ice sheet volume during Laurentide Ice Sheet deglaciation


The contribution of the Greenland and West Antarctic ice sheets to sea level has increased in recent decades, largely owing to the thinning and retreat of outlet glaciers and ice streams. This dynamic loss is a serious concern, with some modelling studies suggesting that the collapse of a major ice sheet could be imminent or potentially underway in West Antarctica, but others predicting a more limited response. A major problem is that observations used to initialize and calibrate models typically span only a few decades, and, at the ice-sheet scale, it is unclear how the entire drainage network of ice streams evolves over longer timescales. This represents one of the largest sources of uncertainty when predicting the contributions of ice sheets to sea-level rise. A key question is whether ice streams might increase and sustain rates of mass loss over centuries or millennia, beyond those expected for a given ocean–climate forcing. Here we reconstruct the activity of 117 ice streams that operated at various times during deglaciation of the Laurentide Ice Sheet (from about 22,000 to 7,000 years ago) and show that as they activated and deactivated in different locations, their overall number decreased, they occupied a progressively smaller percentage of the ice sheet perimeter and their total discharge decreased. The underlying geology and topography clearly influenced ice stream activity, but—at the ice-sheet scale—their drainage network adjusted and was linked to changes in ice sheet volume. It is unclear whether these findings can be directly translated to modern ice sheets. However, contrary to the view that sees ice streams as unstable entities that can accelerate ice-sheet deglaciation, we conclude that ice streams exerted progressively less influence on ice sheet mass balance during the retreat of the Laurentide Ice Sheet.

来源: Nature 浏览次数:0


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