Abstract The marine chromium (Cr) cycle is still insufficiently understood, in particular the mechanisms modulating the spatial distribution of dissolved stable Cr isotopes in seawater. Redox transformations between its main oxidation states, Cr(VI) and Cr(III), have been held accountable for the observed tight inverse logarithmic relationship between the dissolved Cr concentration [Cr] and its isotopic composition (δ53Cr), whereby isotopically light Cr(III) is removed in surface waters and oxygen minimum zones (OMZs), and subsequently released to deeper waters from remineralized particles or sediments. Seawater [Cr] and δ53Cr were investigated in a series of depth profiles across the Peruvian margin OMZ, covering a wide spectrum of dissolved oxygen concentrations ranging from 2 to 242 µmol/kg. We found [Cr] ranging from 1.5 to 5.5 nmol/kg, associated with δ53Cr variations between +1.59 and +0.72‰, but no systematic relationship to dissolved oxygen concentrations. However, distinctly different seawater profiles were observed above the suboxic/anoxic shelf compared to those located further offshore, with substantial Cr removal restricted to suboxic or anoxic environments on the shelf. This suggests that suboxic conditions ([O2]

中文翻译：

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铬还原和相关的稳定同位素分馏仅限于秘鲁最低氧区的缺氧大陆架水域

摘要 海洋铬 (Cr) 循环仍不清楚，特别是调节海水中溶解的稳定 Cr 同位素空间分布的机制。其主要氧化态 Cr(VI) 和 Cr(III) 之间的氧化还原转变已被认为是溶解的 Cr 浓度 [Cr] 与其同位素组成 (δ53Cr) 之间观察到的紧密逆对数关系的原因，其中同位素轻的 Cr( III) 在地表水和最低氧区 (OMZ) 中被去除，然后从再矿化颗粒或沉积物中释放到更深的水域。在秘鲁边缘 OMZ 的一系列深度剖面中对海水 [Cr] 和 δ53Cr 进行了研究，涵盖了从 2 到 242 µmol/kg 的广泛溶解氧浓度范围。我们发现 [Cr] 范围从 1.5 到 5.5 nmol/kg，与 +1.59 和 +0.72‰ 之间的 δ53Cr 变化相关，但与溶解氧浓度没有系统关系。然而，与位于更远海的那些相比，在低氧/缺氧大陆架上方观察到明显不同的海水剖面，大量的铬去除仅限于大陆架上的低氧或缺氧环境。这表明低氧条件 ([O2]