Over the last decades, the chromium (Cr) stable isotope system (referred to as δ53Cr) has emerged as a proxy to reconstruct past oxygenation changes in Earth’s atmosphere and oceans. Although Cr is a promising paleoproxy, uncertainties remain as to the modern marine Cr cycle, and limited data are yet available in large swaths of the ocean, including the Atlantic Ocean. Here we present dissolved seawater Cr concentrations ([Cr]) and δ53Cr along a meridional transect from the North to the South Atlantic (AMT 29). Chromium concentrations range from of 2.51 to 3.96 nmol kg−1 (n = 68) and δ53Cr values range from +0.86 ± 0.04 ‰ (2SEM) to +1.20 ± 0.02 ‰ (2SEM) (n = 68). In contrast to data from other ocean basins [Cr] and δ53Cr show only a weak correlation (δ53Cr vs. Ln([Cr]) R2 = 0.17), inconsistent with a closed-system Rayleigh distillation model. These results can mainly be explained by horizontal advection and water mass mixing, which our data demonstrate are the dominant processes controlling [Cr] and δ53Cr distributions throughout much of the Atlantic, while the impact of in situ biogeochemical cycling is comparatively minor. There is, indeed no clear impact of biological productivity nor of dysoxic environments in the (sub)tropical Atlantic on the cycling of Cr along the transect. This is likely explained by insufficiently depleted oxygen concentrations and relatively low biological productivity, resulting in these processes being of secondary importance relative to water mass mixing in shaping the distribution of Cr in the low- to mid-latitude Atlantic Ocean.

中文翻译：

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大西洋盆地上层水柱中溶解 Cr 分布的控制


在过去的几十年里，铬 （Cr） 稳定同位素系统（称为 δ53Cr）已成为重建地球大气和海洋过去氧合变化的代理。尽管 Cr 是一种很有前途的古替代物，但现代海洋 Cr 循环仍然存在不确定性，包括大西洋在内的大片海洋数据尚有限。在这里，我们展示了从北大西洋到南大西洋沿经向样带 （AMT 29） 的溶解海水 Cr 浓度 （[Cr]） 和 δ53Cr。铬浓度范围为 2.51 至 3.96 nmol kg-1 （n = 68），δ53Cr 值范围为 +0.86 ± 0.04 ‰ （2SEM） 至 +1.20 ± 0.02 ‰ （2SEM） （n = 68）。与来自其他海洋盆地的数据相比，[Cr] 和 δ53Cr 仅显示弱相关性（δ53Cr 与 Ln（[Cr]） R2 = 0.17），与封闭系统瑞利蒸馏模型不一致。这些结果主要可以用水平平流和水团混合来解释，我们的数据表明，这是控制整个大西洋大部分地区 [Cr] 和 δ53Cr 分布的主要过程，而原位生物地球化学循环的影响相对较小。事实上，生物生产力或（亚）热带大西洋的缺氧环境对 Cr 沿横断面的循环没有明显的影响。这可能是由于氧气浓度不足和生物生产力相对较低所解释的，导致这些过程在塑造大西洋中低纬度地区 Cr 的分布时，相对于水团混合来说是次要的。