Marine sulfur cycle evidence for upwelling and eutrophic stresses during Early Triassic cooling events
Marine sulfur cycle evidence for upwelling and eutrophic stresses during Early Triassic cooling events
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DOI：
10.1016/j.earscirev.2018.09.007
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发表时间：
2019-08
影响因子：
12.1
通讯作者：
A. Stebbins;T. Algeo;L. Krystyn;H. Rowe;M. Brookfield;J. Williams;S. Nye;R. Hannigan
中科院分区：
文献类型：
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作者：
A. Stebbins;T. Algeo;L. Krystyn;H. Rowe;M. Brookfield;J. Williams;S. Nye;R. Hannigan
在地球历史上最大的生物危机——二叠纪末大灭绝之后，全球碳和硫循环的扰动在长达5兆r的早三叠纪期间间歇性地反复出现。本研究通过对新特提斯洋南部（印度斯皮提谷）大陆架剖面碳酸盐岩伴生硫酸盐（CAS）硫、CAS氧和黄铁矿硫同位素比值的分析，为早三叠纪海相硫循环提供了新的认识。Spiti地区CAS硫同位素值的长期变化与华南地区相似，表明CAS是全球海水硫酸盐信号的可靠记录者。Spiti CAS和黄铁矿δ34S谱显示黄铁矿埋藏率最高的时期与较低的海表温度一致。我们推断，气候变冷加剧了赤道到极点的温度梯度，增强了温盐翻转环流，并增强了营养物质的上涌，从而刺激了海洋生产力和有机碳沉降通量。生产力的提高促进并维持了微生物的呼吸，增加了对氧的需求，并且在新特提斯南部，导致微生物硫酸盐还原区向上迁移，并与水柱更加紧密地联系在一起。在这些条件下，微生物硫酸盐还原不再受有机质或硫酸盐有效性的限制，导致更多的34s贫黄铁矿被掩埋，海洋硫酸盐池中34s -和18o富集。这一环境情景表明，在Griesbachian-Dienerian、Dienerian-Smithian和Smithian-Spathian边界附近的正碳同位素漂移期间，可能存在与富营养化相关的环境压力。此外，CAS与黄铁矿硫同位素值（Δ34SCAS-pyr）的差异在早三叠世缓慢上升，反映了海水硫酸盐浓度在接近二叠纪-三叠纪边界的最低点之后缓慢上升。
Perturbations to the global carbon and sulfur cycles recurred episodically throughout the ~5-Myr-long Early Triassic, in the aftermath of the end-Permian mass extinction, the largest biocrisis in Earth's history. In this study, analyses of carbonate-associated sulfate (CAS) sulfur, CAS oxygen, and pyrite sulfur-isotope ratios in a continental shelf section from the southern Neo-Tethys Ocean (Spiti Valley, India) provide new insights into the Early Triassic marine sulfur cycle. Secular variation in CAS sulfur-isotope values at Spiti is similar to that in South China, suggesting that CAS was a robust recorder of a global seawater sulfate signal. The Spiti CAS and pyrite δ34S profiles show that the highest rates of pyrite burial coincided with cooler sea-surface temperatures. We infer that climatic cooling steepened equator-to-pole temperature gradients, invigorating thermohaline overturning circulation, and enhancing upwelling of nutrients that stimulated marine productivity and organic carbon sinking fluxes. Enhanced productivity fueled and sustained microbial respiration, increased oxygen demand, and, within the southern Neo-Tethys, caused the zone of microbial sulfate reduction to migrate upwards and become more connected to the water column. Microbial sulfate reduction, under these conditions, was no longer limited by organic matter or sulfate availability, leading to burial of more34S-depleted pyrite and34S- and18O-enrichment of the oceanic sulfate pool. This environmental scenario suggests possible environmental stresses related to eutrophication during positive carbon-isotope excursions around the Griesbachian-Dienerian, Dienerian-Smithian, and Smithian-Spathian boundaries. Additionally, the difference between CAS and pyrite sulfur-isotope values, Δ34SCAS-pyr, slowly rose through the Early Triassic, reflecting a slow increase in seawater sulfate concentrations following a minimum close to the Permian-Triassic boundary.