Investigating the cycling of chromium in the oxygen deficient waters of the Eastern Tropical North Pacific Ocean and the Santa Barbara Basin using stable isotopes
Investigating the cycling of chromium in the oxygen deficient waters of the Eastern Tropical North Pacific Ocean and the Santa Barbara Basin using stable isotopes
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DOI：
10.1016/j.marchem.2020.103756
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发表时间：
2020-04
期刊：
影响因子：
3
通讯作者：
S. B. Moos;E. Boyle;M. Altabet;A. Bourbonnais
中科院分区：
文献类型：
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作者：
S. B. Moos;E. Boyle;M. Altabet;A. Bourbonnais
铬同位素地球化学正在探索的背景下，各种地质问题，以及污染物Cr（VI）的环境修复。在氧化态Cr（VI）还原为还原态Cr（III）的过程中，Cr同位素分馏作用很强。本文介绍了墨西哥外海热带北太平洋东部（ETNP）缺氧区（ODZ）和加州外海圣巴巴拉盆地深处高还原环境（[O2] < 2 μmol/kg）中样品的铬浓度和铬同位素数据。与SAFe站（30°N，140°W）相同密度的好氧沃茨相比，ETNP ODZ上部的总可溶性Cr略有减少（高达0.8 nmol/kg），δ 53 Cr重达0.1-0.2‰，这可能是Cr（VI）减少和通过沉降颗粒去除轻Cr（III）的结果。Cr亏损和Cr同位素分馏在NO3-δ 15 N最高值处达到峰值，在同样缺氧的沃茨中下降，这表明微生物还原依赖于下沉的有机质通量可能是Cr还原的机制。这些数据与净同位素分馏因子ε <$−0.44‰的分馏机制一致。2014年7月，在圣巴巴拉盆地最深的缺氧沃茨中，与相同密度的SAFe站沃茨相比，溶解（<0.2 μm）Cr的贫化高达1.8 nmol/kg，δ 53 Cr的含量高达0.5‰。这与净同位素分馏系数ε −0.65‰一致。在圣巴巴拉盆地现场，这是可能的，非生物的Fe（II）还原（从Fe（II）扩散出来的还原大陆架沉积物）也有助于铬还原除了微生物还原机制。
Cr isotope geochemistry is being explored in the context of a variety of geological problems as well as the environmental remediation of pollutant Cr(VI). There is a strong Cr isotope fractionation during reduction of oxidized Cr(VI) to reduced Cr(III). We present chromium concentration and Cr isotope data for samples from highly reducing environments ([O2] < 2 μmol/kg) in the Eastern Tropical North Pacific (ETNP) Oxygen Deficient Zone (ODZ) off of Mexico and the deep Santa Barbara Basin off of California. Total dissolvable Cr in the upper ETNP ODZ is slightly depleted (by up to 0.8 nmol/kg) and δ53Cr is up to 0.1–0.2‰ heavier compared to oxic waters of the same density seen at the SAFe station (30°N, 140°W), presumably both a result of reduction of Cr(VI) and removal of light Cr(III) by sinking particles. The Cr depletion and Cr isotope fractionation peak at the same depth as the highest δ15N of NO3−and decrease within the equally oxygen-deficient waters below, implying that microbial reduction dependent on the sinking organic matter flux may be the mechanism of Cr reduction. These data are consistent with a fractionation mechanism with a net isotope fractionation factor of ε ≈ −0.44‰. In the deepest anoxic waters of the Santa Barbara Basin in July 2014, dissolved (<0.2 μm) Cr is depleted by up to 1.8 nmol/kg and δ53Cr is up to 0.5‰ heavier compared to SAFe station waters of the same density. This is consistent with a net isotope fractionation factor of ε ≈ −0.65‰. At the Santa Barbara Basin site, it is possible that abiotic Fe(II) reduction (from Fe(II) diffusing out of reducing continental shelf sediments) also contributes to Cr reduction in addition to the microbial reduction mechanism.