BIOLOGICAL IMPACTS ON SERPENTINITE WEATHERING
We completed lizardite and whole serpentinite rock dissolution experiments to test several hypotheses regarding dissolution behavior in the presence of bacteria and organic acids. Our experiments suggest that Fe-oxidizing bacteria accelerate lizardite dissolution rates for the first eight hours of our experiments; however rates are similar after two weeks. Similar experiments show that oxalic acid accelerates lizardite dissolution by less than one order of magnitude. Whole rock serpentinite dissolution experiments examining the effect of 14 different organic acids (acetic, formic, lactic, glycolic, glutamic, oxalic, fumaric, gluconic, citric, malic, methanesulfonic, nonanoic, 2-aminoisobutyric, and valeric acids) on rock dissolution suggest that oxalic, citric, and malic acids are the most effective acids at enhancing weathering at earth surface temperatures.
Field studies of serpentinite weathering in the Klamath Mountains of California and on Little Deer Isle in Maine show that early weathering is driven by the dissolution of Fe-rich pyroxenes. In particular, the presence of ferrous Fe appears to contribute to greater dissolution, whereas the presence of Al within the parent rock appears to contribute to greater stability. Both soils and rock cores at the Klamath sites were tested for the presence of iron oxidizing bacteria which were found to be present in some samples, suggesting that the early alteration of these Fe-rich minerals may be mediated by iron-oxidizing bacteria.