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.

Cr同位素地球化学正在各种地质问题以及污染物Cr（VI）的环境修复的背景下进行探索。在氧化的Cr（VI）还原为Cr（III）的过程中，Cr同位素分馏强烈。我们提供了来自墨西哥东部热带北太平洋（ETNP）缺氧区（ODZ）和深圣巴巴拉盆地深处高度还原环境（[O ₂ ] <2μmol/ kg）的样品的铬浓度和Cr同位素数据加利福尼亚 在上部ETNP ODZ总可溶解的Cr略微耗尽（通过高达0.8纳摩尔/ kg）和δ ⁵³与SAFe站（30°N，140°W）处相同密度的含氧水相比，Cr重达0.1-0.2‰，这大概是Cr（VI）还原和轻铬（III）去除的结果）下沉颗粒。在Cr耗尽和Cr同位素分馏峰在同一深度为最高δ ¹⁵ NO N个₃ ^-低于同样氧不足型的水域内和减小，这意味着微生物减少依赖于下沉有机物通量可Cr的机制减少。这些数据与净同位素分馏因子为ε≈-0.44‰的分馏机理相一致。在2014年7月圣巴巴拉盆地的最深缺氧水域，溶解（<0.2微米）的Cr被至多1.8纳摩尔/ kg和δ耗尽⁵³与相同密度的SAFe站水相比，Cr重达0.5‰。这与ε≈-0.65‰的净同位素分馏因子相符。在圣塔芭芭拉盆地遗址，除微生物还原机制外，非生物的Fe（II）还原（从Fe（II）扩散到减少的陆架沉积物中扩散）也可能有助于Cr的还原。