Geographical variations in Sr and Nd isotopic ratios of cryoconite on Asian glaciers
Geographical variations in Sr and Nd isotopic ratios of cryoconite on Asian glaciers
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DOI：
10.1088/1748-9326/9/4/045007
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发表时间：
2014-04
影响因子：
6.7
通讯作者：
Naoko Nagatsuka;N. Takeuchi;T. Nakano;K. Shin;Emi Kokado
中科院分区：
文献类型：
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作者：
Naoko Nagatsuka;N. Takeuchi;T. Nakano;K. Shin;Emi Kokado
冰尘是一种沉积在冰川表面的深色尘埃，由风吹的矿物颗粒和来自冰川微生物的有机物组成。本文分析了四种矿物组分（即，本文对阿尔泰、帕米尔、天山、祁连山和喜马拉雅等6个亚洲冰川的冰屑岩样品进行了矿物组分（盐、碳酸盐、磷酸盐和硅酸盐矿物组分）和有机组分的分析，并从矿物组分的地质来源和冰川的地球化学过程讨论了它们的地理差异。北部冰川的硅酸盐矿物组分显示出较低的Sr和较高的Nd比值（阿尔泰，87 Sr/86 Sr：0.713 490-0.715 284，εNd（0）：−6.4至−5.6），而位于南部的冰川具有较高的Sr和较低的Nd比值（喜马拉雅山，87 Sr/86 Sr：0.740 121-0.742 088，εNd（0）：−16.4-−15.7）;比值与冰川相应区域的沙漠砂、黄土和河流沉积物相似。这一结果表明，冰屑中的硅酸盐矿物来自不同的来源，这取决于冰川的地理位置。盐，碳酸盐和磷酸盐矿物馏分的同位素比值是不同的硅酸盐馏分，并类似于那些从亚洲沙漠的钙钛矿和磷灰石矿床，但也不同的地理位置，表明它们可能反映其地质起源。有机质组分的Sr同位素比值与中部天山和祁连山冰川的盐水和碳酸盐组分相似，但在北方和南部高于盐水和碳酸盐组分，低于磷酸盐矿物组分。有机组分的比例可以由冰川上微生物掺入的钙源的混合比例来确定。
Cryoconite is a dark-coloured surface dust deposited on glaciers that consists of wind-blown mineral particles, as well as organic matter derived from microbes living on glaciers. In this paper, we analyse the Sr and Nd isotopic ratios of four mineral fractions (i.e., the saline, carbonate, phosphate, and silicate mineral fractions), as well as the organic fraction, of cryoconite samples obtained from six Asian glaciers (the Altai, Pamir, Tien Shan, Qillian Shan, and Himalayan regions), and discuss their geographical variations in terms of the geological origins of the mineral particles and the biogeochemical processes on the glaciers. The silicate mineral fraction showed lower Sr and higher Nd ratios for the glaciers located to the north (Altai, 87Sr/86Sr: 0.713 490–0.715 284, εNd(0): −6.4 to −5.6), while higher Sr and lower Nd ratios for the glaciers located to the south (Himalayas, 87Sr/86Sr: 0.740 121–0.742 088, εNd(0): −16.4 to −15.7); the ratios were similar to those of desert sand, loess, and river sediments in the respective regions of the glaciers. This result suggests that the silicate minerals within the cryoconites were derived from different sources depending on the geographical locations of the glaciers. The isotopic ratios of the saline, carbonate, and phosphate mineral fractions were distinct from those of the silicate fraction, and were similar to those of evaporites and apatite deposits from the Asian deserts, but also varied geographically, indicating that they are likely to reflect their geological origin. The Sr isotopic ratios of the organic fraction were similar to those of the saline and carbonate fractions from glaciers in the central area (Tien Shan and Qillian Shan), but were higher than those of the saline and carbonate fractions, and lower than the phosphate mineral fraction, in the northern and southern areas. The ratios of organic fraction may be determined from the mixing ratio of calcium sources incorporated by microbes on the glaciers.