Organic carbon export from the Greenland ice sheet
Organic carbon export from the Greenland ice sheet
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DOI：
10.1016/j.gca.2013.02.006
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发表时间：
2013-05-15
影响因子：
5
通讯作者：
Kujawinski, Elizabeth B.
中科院分区：
文献类型：
--
作者：
Bhatia, Maya P.;Das, Sarah B.;Kujawinski, Elizabeth B.
冰川融水向海洋系统输出一种独特类型的有机碳，不同于非冰川来源的河流输出，有可能刺激下游海洋初级生产力。本文首次描述了格陵兰冰盖（GrIS）冰川融水的总体溶解有机碳（DOC）和颗粒有机碳（POC）同位素组成。这些数据与早期研究GrIS溶解有机物的分子水平组成相结合，共同描述了融化季节陆地出口冰川冰下排放物中有机碳的浓度、放射性碳含量和不稳定性。通过扩大我们在整个冰盖上的测量，我们估计GrIS的年DOC通量（0.08 Tg/y）与北极一条小河的年DOC通量(流量（Q) < 50 km(3)/y）相当，而GrIS的年POC通量（0.9 Tg/y）可能与北极一条大河的年POC通量（Q > 200 km(3)/y）相当。DOC通量主要来自冰川下（冰下）（约75%）的早期季节，以及在融季高峰时通过冰下环境传输的表面融冰（高达100%）。POC通量主要来自整个融季的冰下环境。与浓度较低（0.1-0.6 mg L-1）且δ C-14更耗尽（δ C-14（DOC）类似于-400 ppm）的旺季（高流量）排放相比，早期（低流量）冰川排放含有更高的DOC浓度（0.5-4.1 mg L-1），并且出口更多的富集碳（δ C-14-(DOC)类似于-250 ppm）。相反，POC输出量（1.4-13.2 mg L-1, δ C-14（POC）类似于-250 ppm）在整个融冰季的浓度或放射性碳含量均无时间变化。伴随样品的溶解离子负荷反映了冰下排水系统的季节演变，证实了冰下水文对整体碳库组成的影响。结果表明：(1)不同的机制控制着冰川系统的DOC和POC通量；(2)不同化学成分的DOC池通过季节变化的水文路径进入；(3) GrIS可以向下游前冰期和海洋环境输送不稳定碳（也可能是14c -贫碳）。(C) 2013 Elsevier Ltd.版权所有。
Glacial meltwater exports a unique type of organic carbon to marine systems, distinct from non-glacially derived riverine export, potentially capable of stimulating downstream marine primary productivity. Here, we describe for the first time the bulk-level dissolved organic carbon (DOC) and particulate organic carbon (POC) isotopic composition of glacial meltwater draining the Greenland ice sheet (GrIS). These data, in conjunction with an earlier study that investigated the molecular-level composition of GrIS dissolved organic matter, collectively describe the concentration, radiocarbon content, and lability of organic carbon in subglacial discharge from a land-terminating outlet glacier during a melt season. By scaling up our measurements across the ice sheet, we estimate that the annual DOC flux from the GrIS (0.08 Tg/y) is equivalent to that from a small Arctic river (discharge (Q) < 50 km(3)/y), and that the annual POC flux from the GrIS (0.9 Tg/y) may be comparable to that of a large Arctic river (Q > 200 km(3)/y). The DOC flux is derived primarily from beneath the glacier (subglacial) (>75%) in the early season, and from surface ice-melt (up to 100%) transmitting through the subglacial environment at the peak of the meltseason. The POC flux is primarily derived from the subglacial environment throughout the meltseason. The early season (low flow) glacier discharge contains higher DOC concentrations (0.5-4.1 mg L-1), and exports more enriched carbon (Delta C-14-(DOC) similar to -250 parts per thousand) compared to the peak season (high flow) discharge, when the concentrations are lower (0.1-0.6 mg L-1) and the Delta C-14 is more depleted (Delta C-14(DOC) similar to -400 parts per thousand). Conversely, the POC export (1.4-13.2 mg L-1, Delta C-14(POC) similar to -250 parts per thousand) shows no temporal variation in either concentration or radiocarbon content throughout the meltseason. Dissolved ion loads in concomitant samples reflected the seasonal evolution of the subglacial drainage system, confirming the influence of subglacial hydrology on the composition of the bulk carbon pools. Based on this work, we conclude that (1) different mechanisms control the DOC and POC flux from glacial systems; (2) chemically-distinct DOC pools are accessed by seasonally-evolving hydrological flow-paths; and (3) the GrIS can deliver labile carbon, which may also be 14 C-depleted, to downstream proglacial and marine environments. (C) 2013 Elsevier Ltd. All rights reserved.