研究業績

Marine authigenic clay formation has the potential to balance global ocean budgets of K and Mg. However, the fluxes of K and Mg uptake into marine sediment, particularly in the abyssal ocean, is poorly constrained. In this study, we perform multivariate statistics on a geochemical dataset of ∼ 2000 abyssal marine sediment samples from 67 sites in the Pacific Ocean to determine the magnitude of dust, volcanic ash, and “excess” K and “excess” Mg in each sample. Results illustrate the prevalence of different types of volcanic ash in marine sediment across the Pacific Ocean over the Cenozoic. Continental and volcanic sources, however, cannot explain all the K and Mg in marine sediment. We interpret the “excess” K and Mg in marine sediment as originating from seawater. The highest mass fractions of excess K and Mg are in samples that also have biogenic SiO2 and/or Fe-Mn oxides. From the solid-phase sediment, we estimate the geologically-modern fluxes of seawater K and Mg into silica-rich, abyssal marine sediment to be 0.032 ± 0.027 Tmol of K/yr and 0.067 ± 0.058 Tmol of Mg/yr. The highest rates of Mg and K uptake seem to be episodic and dependent on local conditions and sedimentation rates. The majority of samples have modest uptakes of Mg and K from seawater, but show an overall decrease from the early Cenozoic to modern. If the K and Mg from seawater was taken up into a marine authigenic clay via a reverse weathering reaction, the results support a decline in reverse weathering over the Cenozoic.