Meteoric 10Be as a tracer of subglacial processes and interglacial surface exposure in Greenland
Meteoric 10Be as a tracer of subglacial processes and interglacial surface exposure in Greenland
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DOI：
10.1016/j.quascirev.2018.05.009
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发表时间：
2018-07-01
影响因子：
4
通讯作者：
Neumann, Thomas A.
中科院分区：
文献类型：
--
作者：
Graly, Joseph A.;Corbett, Lee B.;Neumann, Thomas A.
为了测试格陵兰岛目前有冰川覆盖的区域所产生的沉积物在之前的间冰期是否暴露在地球表面附近或地球表面，我们测量了在五个冰缘地点采集的沉积物颗粒涂层中所含的稀有同位素铍 - 10。这种颗粒涂层含有大气成因铍 - 10（Be - 10(met)），它在大气中形成并沉积在地球表面。样本包括夹带在冰中的沉积物、在冰缘采集的冰水沉积物以及在消融区通过热水钻探提取的冰下沉积物。由于被冰掩埋，当代冰下沉积物只有在过去格陵兰冰盖比现在范围小的时候才可能获得大量的大气成因铍 - 10浓度。所测得的最高大气成因铍 - 10浓度与在发育良好、长期暴露的土壤中发现的浓度相当，这表明在冰期前或间冰期暴露的沉积物在冰下得以保存并被冰川搬运。冰内沉积物的大气成因铍 - 10浓度明显高于冰水沉积物，这表明冰水作用的侵蚀性很强，足以去除之前间冰期暴露的示踪物。格陵兰岛北部从冰盖中央主穹顶供应冰和沉积物的地点的大气成因铍 - 10浓度明显高于格陵兰岛南部的地点，这表明格陵兰岛中部比南部在冰期前或间冰期的地貌保存得更好。由于格陵兰岛南部冰川消退的频率更高且在空间上范围更广，但过去地表暴露的证据却更少，我们认为冰川沉积物中的大气成因铍 - 10测量值主要受侵蚀效率的控制，而非间冰期暴露时长的控制。（C）2018爱思唯尔有限公司。保留所有权利。
In order to test whether sediment emerging from presently glaciated areas of Greenland was exposed near or at Earth's surface during previous interglacial periods, we measured the rare isotope Be-10 contained in grain coatings of sediment collected at five ice marginal sites. Such grain coatings contain meteoric Be-10 (Be-10(met)), which forms in the atmosphere and is deposited onto Earth's surface. Samples include sediment entrained in ice, glaciofluvial sediment collected at the ice margin, and subglacial sediment extracted during hot water drilling in the ablation zone. Due to burial by ice, contemporary subglacial sediment could only have acquired substantial Be-10(met) concentrations during periods in the past when the Greenland Ice Sheet was less extensive than present.The highest measured Be-10(met) concentrations are comparable to those found in well-developed, long-exposed soils, suggesting subglacial preservation and glacial transport of sediment exposed during preglacial or interglacial periods. Ice-bound sediment has significantly higher Be-10(met) concentrations than glaciofluvial sediment, suggesting that glaciofluvial processes are sufficiently erosive to remove tracers of previous interglacial exposures. Northern Greenland sites where ice and sediment are supplied from the ice sheet's central main dome have significantly higher Be-10(met) concentrations than sites in southern Greenland, indicating greater preglacial or interglacial landscape preservation in central Greenland than in the south. Because southern Greenland has more frequent and spatially extensive periods of glacial retreat but nevertheless has less evidence of past subaerial exposure, we suggest that Be-10(met) measurements in glacial sediment are primarily controlled by erosional efficiency rather than interglacial exposure length. (C) 2018 Elsevier Ltd. All rights reserved.