Cadmium-isotopic evidence for increasing primary productivity during the Late Permian anoxic event
Cadmium-isotopic evidence for increasing primary productivity during the Late Permian anoxic event
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DOI：
10.1016/j.epsl.2014.11.010
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发表时间：
2015-01
影响因子：
5.3
通讯作者：
S. Georgiev;T. Horner;H. Stein;J. Hannah;B. Bingen;M. Rehkämper
中科院分区：
文献类型：
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作者：
S. Georgiev;T. Horner;H. Stein;J. Hannah;B. Bingen;M. Rehkämper
地球上最极端的灭绝事件发生在晚二叠世末期，导致90%以上的现存海洋物种灭绝。大范围和密集的海洋缺氧几乎肯定是造成这场灾难的原因，尽管维持这种条件的驱动机制仍然存在争议。特别感兴趣的是水柱缺氧是否是一个“停滞的海洋”的后果，或者如果它是由营养供应，初级生产力，以及随后的异养呼吸增加控制。测试这些相互竞争的假设需要从海洋沉积物中地表水生产力的变化中去卷积沉积/底层水氧化还原条件。我们通过研究格陵兰东部和挪威大陆架中部的海洋页岩，并结合沉积氧化还原指标和镉同位素分析来解决这个问题。沉积氮同位素数据，黄铁矿framboid分析，有机和无机页岩地球化学揭示硫化物条件下，强烈的上升流，越来越缺氧的条件下，加强上升流在格陵兰岛和挪威部分，分别。沉积金属收支的详细分析表明，镉主要与有机碳和记录主要的地球化学特征，从而使重建地表水养分利用。对反王水溶出的自生页岩组分进行镉同位素分析，得出δ Cd 114/110平均值为+ 0.15±0.01‰（2 SE，n= 12; rel. NIST SRM 3108），表明地表水养分利用不完全。营养盐利用率的恒定程度结合强烈的上升流需要增加初级生产力，而不是海洋滞流，以平衡更大的营养盐通量的两个研究地点在晚二叠世水柱缺氧的发展。总体而言，我们的数据表明，如果底层水氧化还原和上升流能够得到充分限制，则富含有机物沉积物的镉同位素分析可用于提供有关营养物利用以及过去生产力的有价值信息。
Earth's most extreme extinction event near the end of the Late Permian decimated more than 90% of all extant marine species. Widespread and intensive oceanic anoxia almost certainly contributed to the catastrophe, though the driving mechanisms that sustained such conditions are still debated. Of particular interest is whether water column anoxia was a consequence of a ‘stagnant ocean’, or if it was controlled by increases in nutrient supply, primary productivity, and subsequent heterotrophic respiration. Testing these competing hypotheses requires deconvolving sedimentary/bottom water redox conditions from changes in surface water productivity in marine sediments. We address this issue by studying marine shales from East Greenland and the mid-Norwegian shelf and combining sedimentary redox proxies with cadmium-isotopic analyses. Sedimentary nitrogen-isotopic data, pyrite framboid analyses, and organic and inorganic shale geochemistry reveal sulfidic conditions with vigorous upwelling, and increasingly anoxic conditions with a strengthening upwelling in the Greenland and Norwegian sections, respectively. Detailed analysis of sedimentary metal budgets illustrates that Cd is primarily associated with organic carbon and records primary geochemical signatures, thus enabling reconstruction of surface water nutrient utilization. Cadmium-isotopic analyses of the authigenic shale fraction released by inverse aqua regia digestion yield an average δ Cd 114/110 of+ 0.15±0.01‰(2 SE, n= 12; rel. NIST SRM 3108), indicative of incomplete surface water nutrient utilization up-section. The constant degree of nutrient utilization combined with strong upwelling requires increasing primary productivity–and not oceanic stagnation–to balance the larger nutrient fluxes to both study sites during the development of the Late Permian water column anoxia. Overall, our data illustrate that if bottom water redox and upwelling can be adequately constrained, Cd-isotopic analyses of organic-rich sediments can be used to provide valuable information on nutrient utilization and therefore past productivity.