HR: 08:50h
AN: OS51D-04    [Abstracts]
TI: The Impact of Microbes on the Composition of the Ocean Crust and Seawater
AU: * Fisk, M
EM: mfisk@coas.oregonstate.edu
AF: Oregon State University, 104 Ocean Admin Bldg College of Ocean and Atm Sci Oregon State University, Corvallis, OR 97331-5503 United States
AU: Josef, J
EM: jjosef@coas.oregonstate.edu
AF: Oregon State University, 104 Ocean Admin Bldg College of Ocean and Atm Sci Oregon State University, Corvallis, OR 97331-5503 United States
AU: Storrie-Lombardi, M
EM: mike@kinohi.org
AF: Kinohi Institute, Kinohi Institute 530 S. Lake Aveneu, Pasadena, CA 91101 United States
AB: Microbes attack volcanic glass and primary igneous minerals in aqueous environments and they participate in the transformation of glass and minerals into secondary minerals such as clay. This transformation also proceeds in the absence of microbes. In either case some elements go into solution and others are sequestered in secondary minerals. Our hypothesis is that in the ocean crust secondary minerals produced by abiotic reactions are chemically distinct from those produced by microbial attack. If this is true, then microbial attack on volcanic rocks could affect the composition of the ocean crust and sea water. The best source of deep sea volcanic rocks to test this hypotheses is the Ocean Drilling Program's archived collection. We selected several samples from this collection and used an electron microprobe to measure the composition of secondary clays that were deemed to be produced either bioticly or abioticly. Abundance measurements were obtained for eleven elements (Na, Mg, Al, Si, P, Cl, K, Ca, Ti, Mn, and Fe). We used Principal Component Analysis to extract three factors that were linear combinations of the eleven elements and that accounted for more than 80% of the data variance. These three factors were used as inputs to a stochastic, non-linear, Artificial Neural Network that demonstrates that abiotic secondary minerals are chemically distinct from biotic secondary minerals. Significant differences in clay compositions were found for MgO (0.2), MnO (0.3), K$_{2}$O (3), CaO (2), TiO$_{2}$ (3), and possibly FeO (1.2). (Numbers in parentheses are biotic:abiotic oxide wt. % ratios.) This result suggests that biotic alteration of the ocean crust will release more MgO and MnO from the rocks and sequester more K$_{2}$O, CaO, TiO$_{2}$, and possibly FeO in clay than abiotic alteration. The impact of microbial alteration on the composition of the crust therefore depends on the fraction of basalt alteration that is caused by microbes. The impact of microbial alteration on the composition of sea water, also depends on this fraction, and whether released elements Mg and K are sequestered elsewhere in the crust or are vented to the ocean.
DE: 4805 Biogeochemical cycles (1615)
DE: 4832 Hydrothermal systems
DE: 3655 Major element composition
DE: 4803 Bacteria
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting