Abstract
The oceanic magnesium cycle is largely controlled by continental weathering and marine authigenic mineral formation, which are intimately linked to long-term climate. Uncertainties in the magnesium cycle propagate into other chemical budgets, and into interpretations of paleo-oceanographic reconstructions of seawater δ26Mg and Mg/Ca ratios. Here, we produce a detailed global map of the flux of dissolved magnesium from the ocean into deeper marine sediments (greater than ∼1 meter below seafloor), and quantify the global flux and associated isotopic fractionation. We find that this flux accounts for 15–20% of the output of magnesium from the ocean, with a flux-weighted fractionation factor of ∼0.9994 acting to increase the magnesium isotopic ratio in the ocean. Our analysis provides the best constraints to date on the sources and sinks that define the oceanic magnesium cycle, including new constraints on the output flux of magnesium and isotopic fractionation during low-temperature ridge flank hydrothermal circulation.
Highlights
The oceanic magnesium cycle is largely controlled by continental weathering and marine authigenic mineral formation, which are intimately linked to long-term climate
Authigenic aluminosilicate formation is a potentially important sink for magnesium in marine sediments, where it can be incorporated into the authigenic phase in a greater stoichiometric ratio than in the original primary silicate from which it formed, resulting in the release of calcium and other cations to pore waters[25]
The flux of dissolved magnesium into marine sediments from the overlying ocean is widely driven by molecular diffusion that occurs as pore water magnesium is depleted during authigenic mineral formation in the sediment column, as well as the direct burial of seawater as pore water that results from sediment accumulation on the seafloor
Summary
The oceanic magnesium cycle is largely controlled by continental weathering and marine authigenic mineral formation, which are intimately linked to long-term climate. The flux of dissolved magnesium into marine sediments from the overlying ocean is widely driven by molecular diffusion that occurs as pore water magnesium is depleted during authigenic mineral formation in the sediment column, as well as the direct burial of seawater as pore water that results from sediment accumulation on the seafloor. This global flux of magnesium into marine sediments has been demonstrated to be a potentially important part of the oceanic magnesium cycle[30,31,32]. After undergoing alteration during sediment diagenesis, much of the chemically and isotopically altered pore water eventually returns to the ocean in its altered form during compaction at subduction zones and other compressive tectonic regimes
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