More Than Deoxygenation: Linking Iodate Reduction to Nitrogen, Iron, and Sulfur Chemistry in Reducing Regimes

IF 3.3 2区 地球科学 Q1 OCEANOGRAPHY Journal of Geophysical Research-Oceans Pub Date : 2024-11-01 DOI:10.1029/2024JC021013
Natalya Evans, Emma Johnson, Amanda Taing, Alexi A. Schnur, Peter J. Chace, Samantha Richards, Dalton S. Hardisty, James W. Moffett
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Abstract

A striking feature of Oxygen Deficient Zones (ODZs) on the eastern boundary of the Pacific Ocean are large subsurface plumes of iodide. Throughout the oceans, iodate is the predominant and thermodynamically favored species of dissolved iodine, but iodate is depleted within these plumes. The origin of iodide plumes and mechanism of reduction of iodate to iodide remains unclear but is thought to arise from a combination of in situ reduction and inputs from reducing shelf sediments. To distinguish between these sources, we investigated iodine redox speciation along the Oregon continental shelf. This upwelling system resembles ODZs but exhibits episodic hypoxia, rather than a persistently denitrifying water column. We observed elevated iodide in the benthic boundary layer overlying shelf sediments, but to a much smaller extent than within ODZs. There was no evidence of offshore plumes of iodide or increases in total dissolved iodine. Results suggest that an anaerobic water column dominated by denitrification, such as in ODZs, is required for iodate reduction. However, re-analysis of iodine redox data from previous ODZ work suggests that most iodate reduction occurs in sediments, not the water column, and is also decoupled from denitrification. The underlying differences between these regimes have yet to be resolved, but could indicate a role for reduced sulfur in iodate reduction if the sulfate reduction zone is closer to the sediment-water interface in ODZ shelf sediments than in Oregon sediments. Iodate reduction is not a simple function of oxygen depletion, which has important implications for its application as a paleoredox tracer.

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不仅仅是脱氧:将还原体系中的碘酸盐还原与氮、铁和硫化学联系起来
太平洋东部边界缺氧区(ODZs)的一个显著特点是大量的次表层碘化物羽流。在整个大洋中,碘酸根是溶解碘的主要和热力学上有利的物种,但在这些羽流中,碘酸根会被耗尽。碘化物羽流的来源以及碘酸根还原成碘化物的机制仍不清楚,但认为是原地还原和陆架沉积物还原输入的综合结果。为了区分这些来源,我们对俄勒冈大陆架沿岸的碘氧化还原标本进行了调查。这一上升流系统与 ODZ 相似,但表现为偶发性缺氧,而不是持续的反硝化水柱。我们在陆架沉积物上覆的海底边界层观察到碘化物升高,但其程度远小于 ODZs。没有证据表明近海存在碘化物羽流或溶解碘总量增加。结果表明,碘酸盐还原需要一个以反硝化作用为主的厌氧水体,如 ODZs。然而,对以前 ODZ 工作中的碘氧化还原数据进行的重新分析表明,大部分碘还原发生在沉积物中,而不是水体中,而且也与反硝化作用脱钩。这些机制之间的根本差异尚待解决,但如果与俄勒冈州沉积物相比,奥德赛大陆架沉积物中的硫酸盐还原区更接近沉积物-水的界面,则可能表明还原硫在碘还原中的作用。碘酸盐还原作用不是耗氧的简单函数,这对其作为古氧化还原示踪剂的应用具有重要影响。
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来源期刊
Journal of Geophysical Research-Oceans
Journal of Geophysical Research-Oceans Earth and Planetary Sciences-Oceanography
CiteScore
7.00
自引率
13.90%
发文量
429
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