Department of Geology and Geophysics, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, MA, 02543, USA.
Department of Earth and Environment, Boston University, 685 Commonwealth Ave., Boston, MA, 02215, USA.
Nat Commun. 2017 Oct 10;8(1):844. doi: 10.1038/s41467-017-00853-5.
Authigenic clay minerals formed on or in the seafloor occur in every type of marine sediment. They are recognized to be a major sink of many elements in the ocean but are difficult to study directly due to dilution by detrital clay minerals. The extremely low dust fluxes and marine sedimentation rates in the South Pacific Gyre (SPG) provide a unique opportunity to examine relatively undiluted authigenic clay. Here, using Mg isotopes and element concentrations combined with multivariate statistical modeling, we fingerprint and quantify the abundance of authigenic clay within SPG sediment. Key reactants include volcanic ash (source of reactive aluminium) and reactive biogenic silica on or shallowly buried within the seafloor. Our results, together with previous studies, suggest that global reorganizations of biogenic silica burial over the Cenozoic reduced marine authigenic clay formation, contributing to the rise in seawater Mg/Ca and decline in atmospheric CO over the past 50 million years.Reverse weathering reactions on or in the seafloor are a major sink of many elements and alkalinity in seawater. Here, the authors show how reduced rates of reverse weathering may be responsible for global cooling and increased seawater Mg/Ca over the past 50 million years.
自生黏土矿物在海底或海底形成，存在于每一种海洋沉积物中。它们被认为是海洋中许多元素的主要汇，但由于与碎屑黏土矿物的稀释作用，难以直接研究。南太平洋环流（SPG）中极低的尘埃通量和海洋沉积速率为研究相对未稀释的自生黏土提供了独特的机会。在这里，我们使用镁同位素和元素浓度结合多元统计模型，对 SPG 沉积物中自生黏土的丰度进行了特征分析和量化。关键反应物包括火山灰（反应性铝的来源）和海底表面或浅层埋藏的反应性生物硅。我们的结果与以前的研究一起表明，新生代生物硅埋藏的全球重组减少了海洋自生黏土的形成，导致过去 5000 万年海水镁钙比和大气 CO2 的上升。海底或海底的反向风化反应是海水中许多元素和碱度的主要汇。在这里，作者表明，过去 5000 万年中，反向风化速率的降低可能是全球变冷和海水镁钙比增加的原因。
