We find that the net flux into the modern seafloor acts to increase the magnesium isotopic ratio in the ocean, reflecting greater fractionation due to authigenic carbonate formation compared to aluminosilicate formation in the upper sediment column at most sites.

The oceanic magnesium cycle is largely controlled by continental weathering and marine authigenic mineral formation, which are intimately linked to long-term climate.

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 use the model, together with measured magnesium concentration and δ 26 Mg profiles to quantify rates of net magnesium cycling and try and identify net magnesium sources and sinks in the sediment column and underlying crust.

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 ...