Siegert M J
Bristol Glaciology Centre, School of Geographical Sciences, University of Bristol, UK.
Sci Prog. 2000;83 ( Pt 3):223-42.
At the floor of the Antarctic ice sheet, 4 km below the Russian research base Vostok Station, lies a 2,000 km3 body of water, comparable in size to Lake Ontario. This remote water mass, named Lake Vostok, is the world's largest subglacial lake by an order of magnitude (Figure 1). Despite ice-surface temperatures regularly around -60 degrees C, the ice-sheet base is kept at the melting temperature by geothermal heating from the Earth's interior. The ice sheet above the lake has been in existence for at least several million years and possibly as long as 20 million years. The origins of Lake Vostok may therefore data back across geological time to the Miocene (7-26 Ma). The hydrology of Lake Vostok can be characterised by subglacial melting across its northern side, and refreezing over the southern section. A deep ice core, located over the southern end of the lake has sampled the refrozen ice. Geochemical analysis of this ice has found that it comprises virtually pure water. However, normal glacier ice contains impurities such as debris and gas hydrates. Subglacial melting and freezing over Lake Vostok may, therefore, leave the lake enriched in potential nutrients issued from the melted glacier ice. Many scientists expect microbial life to exist within the lake, adapted to the extreme conditions of low nutrient and energy levels. Indeed microbes have been found in the basal refrozen layers of the ice sheet. If Lake Vostok has been isolated from the atmosphere for several million years by the ice sheet that lays above it, the microbes within the lake must also date back several million years and may have undergone evolution over this time, yielding life that may be unique to Lake Vostok. Plans are currently being arranged to explore Lake Vostok and other Antarctic subglacial lakes, and identify life in these extraordinary places. Before this happens, however, much more needs to be known about the ice-sheet above subglacial lakes, and the rocks and sediment below them.
在俄罗斯沃斯托克站下方4公里处的南极冰盖底部，有一个体积达2000立方公里的水体，其大小与安大略湖相当。这个偏远的水体被称为沃斯托克湖，是世界上最大的冰下湖，比其他冰下湖大一个数量级（图1）。尽管冰面温度经常在零下60摄氏度左右，但冰盖底部由于地球内部的地热加热而保持在融化温度。湖上方的冰盖已经存在了至少几百万年，可能长达2000万年。因此，沃斯托克湖的起源可以追溯到地质时期的中新世（700 - 2600万年前）。沃斯托克湖的水文特征表现为湖的北侧发生冰下融化，而南侧则重新冻结。位于湖南端上方的一个深冰芯对重新冻结的冰进行了采样。对该冰的地球化学分析发现，它几乎由纯水组成。然而，正常的冰川冰含有诸如碎屑和气体水合物等杂质。因此，沃斯托克湖上方的冰下融化和冻结可能会使湖中富含从融化的冰川冰中释放出的潜在营养物质。许多科学家预计湖内存在微生物生命，它们适应了低营养和低能量水平的极端条件。事实上，在冰盖底部重新冻结的冰层中已经发现了微生物。如果沃斯托克湖通过其上方的冰盖与大气隔绝了数百万年，那么湖中的微生物也一定可以追溯到数百万年前，并且可能在这段时间里经历了进化，产生了可能是沃斯托克湖特有的生命形式。目前正在安排计划探索沃斯托克湖和其他南极冰下湖，并确定这些非凡地方的生命形式。然而，在这之前，需要更多地了解冰下湖上方的冰盖以及其下方的岩石和沉积物。
