Within the altered parts of the glass rim of pillow lavas of Hole 896A, at depths at least 432 m below seafloor (237 m below the top of volcanic basement), microbes have been identified. This is indicated by the size and shapes of alteration textures and verified by the presence of DNA and extreme accumulation of K₂O. This demonstrates the existence of a volcanic subterranean biosphere. The microbially processed parts of the glass show wide scatter with respect to all major elements, which may be attributed to active cells. Compared to the host basaltic glass, CaO and Na₂O are invariably depleted, as are SiO₂ and MgO generally. Al₂O₃, FeO(t), and TiO₂ show either depletion or enrichment, K₂O is invariably enriched, and P₂O₅ may be enriched. Microbes living on, and causing dissolution of, basaltic glass may accommodate elements released from it within the cells, and thus function as individual element reservoirs. Microbes may also produce precipitates or water-soluble compounds. Hence, the microbial alteration of basaltic glass, which comprises a substantial volume of the volcanic component of the oceanic crust and an enormous surface area, may have a significant bearing on the mechanism for chemical exchange between oceanic crust and ocean water.

Date of initial receipt: 25 July 1994
Date of acceptance: 15 November 1994

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