Exploring former subglacial Hodgson Lake, Antarctica Paper I: site description, geomorphology and limnology
Exploring former subglacial Hodgson Lake, Antarctica Paper I: site description, geomorphology and limnology
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DOI：
10.1016/j.quascirev.2009.04.011
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发表时间：
2009-11
影响因子：
4
通讯作者：
D. Hodgson;S. Roberts;M. J. Bentley;James R. Smith;Joanne S. Johnson;E. Verleyen;W. Vyverman;A. Hodson;M. Leng;A. Cziferszky;A. Fox;D. Sanderson
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文献类型：
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作者：
D. Hodgson;S. Roberts;M. J. Bentley;James R. Smith;Joanne S. Johnson;E. Verleyen;W. Vyverman;A. Hodson;M. Leng;A. Cziferszky;A. Fox;D. Sanderson
在南极冰盖退缩的边缘，有许多地方从前的冰下湖泊从冰下冒出来，但仍然常年被冰覆盖。本文介绍了其中一个湖泊的地点描述，霍奇森湖位于南极半岛西部亚历山大岛南部（南纬72°00.549′，西经68°27.708′）。首先，我们利用地形和地貌图描述湖泊的物理环境。其次，我们利用冰川不稳定的宇宙成因同位素定年与冰消退期间形成的凸起湖岸线三角洲的光激发光定年相互参照，确定了当地冰盖的消冰历史和湖泊的出现。第三，描述了物理和化学湖沼学，包括生命的生物和生物地球化学证据。结果表明，在13.5ka时，霍奇森湖的冰层厚度至少为295m，在全新世期间逐渐变薄，4.6ka后的某个时间，湖冰覆盖高度达到比现在的湖冰高6.5m。厚厚的常年冰覆盖至今仍在湖面上，湖水与大气隔绝，其化学成分与集水区冰的冰下融化一致。该湖是超贫营养湖泊，营养物质浓度在冰川下的沃斯托克湖的湖冰中发现的范围内。总有机碳和溶解有机碳存在，但浓度低于大陆降雨中通常记录的浓度。利用光学显微镜和高效液相色谱法在水柱中未检测到与光合作用或细菌活性相关的生物和色素。深层so4和阳离子浓度的增加以及o2的下降为硫化物氧化和细菌对o2的微小需求提供了一些证据，这些需求导致碳生物地球化学中微小的、可能无法检测到的变化。然而，总的来说，生命的化学标志是不确定的，非生物过程，如孔隙水从底栖沉积物扩散到湖中，更有可能是深层离子浓度增加的原因。这项研究的下一阶段将是对湖泊沉积物进行古湖泊学研究，看看它们能揭示冰川下湖泊的历史，并对湖水和底栖生物进行详细的分子分析，以确定存在什么样的生命形式。结合起来，这些研究将测试一些将用于探索大陆冰川下深层湖泊的方法。
At retreating margins of the Antarctic Ice Sheet, there are a number of locations where former subglacial lakes are emerging from under the ice but remain perennially ice-covered. This paper presents a site description of one of these lakes, Hodgson Lake, situated on southern Alexander Island, west of the Antarctic Peninsula (72° 00.549′ S, 68° 27.708′ W). First, we describe the physical setting of the lake using topographic and geomorphological maps. Second, we determine local ice sheet deglaciation history and the emergence of the lake using cosmogenic isotope dating of glacial erratics cross-referenced to optically stimulated luminescence dating of raised lake shoreline deltas formed during ice recession. Third we describe the physical and chemical limnology including the biological and biogeochemical evidence for life. Results show that the ice mass over Hodgson Lake was at least 295m thick at 13.5ka and has progressively thinned through the Holocene with the lake ice cover reaching an altitude of c. 6.5m above the present lake ice sometime after 4.6ka. Thick perennial ice cover persists over the lake today and the waters have remained isolated from the atmosphere with a chemical composition consistent with subglacial melting of catchment ice. The lake is ultra-oligotrophic with nutrient concentrations within the ranges of those found in the accreted lake ice of subglacial Lake Vostok. Total organic carbon and dissolved organic carbon are present, but at lower concentrations than typically recorded in continental rain. No organisms and no pigments associated with photosynthetic or bacterial activity were detected in the water column using light microscopy and high performance liquid chromatography. Increases in SO4and cation concentrations at depth and declines in O2provide some evidence for sulphide oxidation and very minor bacterial demand upon O2that result in small, perhaps undetectable changes in the carbon biogeochemistry. However, in general the chemical markers of life are inconclusive and abiotic processes such as the diffusion of pore waters into the lake from its benthic sediments are far more likely to be responsible for the increased concentrations of ions at depth. The next phases of this research will be to carry out a palaeolimnological study of the lake sediments to see what they can reveal about the history of the lake in its subglacial state, and a detailed molecular analysis of the lake water and benthos to determine what forms of life are present. Combined, these studies will test some of the methodologies that will be used to explore deep continental subglacial lakes.