Elemental data for composites from DSDP Sites 417A, 417D, and 418A

Using the major-element budget of seafloor alteration of the upper 500 m of 120-Ma-old oceanic crust at DSDP/ODP Sites 417A, 417D and 418A in the central western Atlantic, we estimate the acidity flux associated with the low-temperature weathering of the upper oceanic crust. The acidity flux is calculated based on major-element fluxes and charge-balance considerations.

The relevant chemical fluxes from seawater to the upper crust are 4.1+-0.1; 1.4+-1.4; 2.2+-0.6 and -12+-2 10**11 mol/yr for K, Mg, Na and silicate-Ca, respectively. The associated acidity flux is (3.5+-3)10**11 eq/y. Relative to continental weathering, these fluxes are significant for K and silicate-Ca, but are minor for Na, Mg and acidity.