Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, New York 10964, USA.
Department of Earth and Environmental Sciences, Columbia University, Palisades, New York, New York 10964, USA.
Nature. 2017 Apr 19;544(7650):344-348. doi: 10.1038/nature22048.
Meltwater stored in ponds and crevasses can weaken and fracture ice shelves, triggering their rapid disintegration. This ice-shelf collapse results in an increased flux of ice from adjacent glaciers and ice streams, thereby raising sea level globally. However, surface rivers forming on ice shelves could potentially export stored meltwater and prevent its destructive effects. Here we present evidence for persistent active drainage networks-interconnected streams, ponds and rivers-on the Nansen Ice Shelf in Antarctica that export a large fraction of the ice shelf's meltwater into the ocean. We find that active drainage has exported water off the ice surface through waterfalls and dolines for more than a century. The surface river terminates in a 130-metre-wide waterfall that can export the entire annual surface melt over the course of seven days. During warmer melt seasons, these drainage networks adapt to changing environmental conditions by remaining active for longer and exporting more water. Similar networks are present on the ice shelf in front of Petermann Glacier, Greenland, but other systems, such as on the Larsen C and Amery Ice Shelves, retain surface water at present. The underlying reasons for export versus retention remain unclear. Nonetheless our results suggest that, in a future warming climate, surface rivers could export melt off the large ice shelves surrounding Antarctica-contrary to present Antarctic ice-sheet models, which assume that meltwater is stored on the ice surface where it triggers ice-shelf disintegration.
储存在池塘和裂缝中的融水会削弱和断裂冰架，引发其快速解体。这种冰架崩塌导致来自相邻冰川和冰流的冰通量增加，从而使全球海平面上升。然而，在冰架上形成的地表河流可能会潜在地输出储存的融水并防止其产生破坏性影响。在这里，我们提供了在南极洲纳森冰架上存在持久的活跃排水网络（相互连接的溪流、池塘和河流）的证据，这些网络将冰架的大部分融水输出到海洋中。我们发现，活跃的排水系统通过瀑布和落水洞将水从冰面排出已经有一个多世纪了。这条地表河流终止于一个 130 米宽的瀑布，在七天的时间内可以排出整个年度的地表融水。在较温暖的融化季节，这些排水网络通过更长时间的活跃和更多的水输出来适应不断变化的环境条件。在格陵兰的彼得曼冰川前的冰架上也存在类似的网络，但拉森 C 和阿梅里冰架等其他系统目前则保留了地表水。地表水输出和保留的根本原因仍不清楚。尽管如此，我们的研究结果表明，在未来的气候变暖中，地表河流可能会将融水从环绕南极洲的大型冰架上输出——这与目前的南极冰架模型相反，后者假设融水储存在冰面上，从而引发冰架解体。
