Biologically mediated dissolution of volcanic glass in seawater

We studied the effects of biological mediation on the dissolution of basalt ic glass in seawater. Experiments with typical seawater microbial populatio ns were contrasted with a sterile control, and reactions were monitored che mically and isotopically. Biologically mediated experiments produce twice t he mass of authigenic phases than abiotic experiments and the phases are di fferent. Abiotic alteration of glass dissolves basaltic Si and Ca and scave nges seawater Mg, while biotic alteration removes Ca from seawater. Such op posing behavior of Ca and Mg in biotic and abiotic alteration of basaltic g lass may have important implications for the carbon cycle and the exchange processes between ocean crust and seawater. Sr-87/Sr-86 data of glass and a lteration products suggest that biological mediation enhances both the diff usion 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 implie s that chemical fluxes from water-rock interaction at low temperatures may change as life on Earth evolves. (C) 1998 Elsevier Science B.V. All rights reserved.