Biologically mediated dissolution of volcanic glass in seawater

We studied the effects of biological mediation on the dissolution of basaltic glass in seawater. Experiments with typical seawater microbial populations were contrasted with a sterile control, and reactions were monitored chemically and isotopically. Biologically mediated experiments produce twice the mass of authigenic phases than abiotic experiments and the phases are different. Abiotic alteration of glass dissolves basaltic Si and Ca and scavenges seawater Mg, while biotic alteration removes Ca from seawater. Such opposing behavior of Ca and Mg in biotic and abiotic alteration of basaltic glass may have important implications for the carbon cycle and the exchange processes between ocean crust and seawater. 87Sr/86Sr data of glass and alteration products suggest that biological mediation enhances both the diffusion of seawater Sr into glass by a factor of 3–4, and the dissolution of basaltic Sr into seawater by a factor of 20–40. The dependence of chemical exchange processes between seawater and glass on biological activity implies that chemical fluxes from water–rock interaction at low temperatures may change as life on Earth evolves.