ROCK-HOSTED HYDROTHERMAL ECOSYSTEMS I: HIGH-TEMPERATURE DEEP-SEA SULFIDE CHIMNEYS

Deep-sea hydrothermal vents are a system of striking contrasts, where high-temperature, highly-reduced, metal-rich fluids mix with cold, oxygenated seawater. The environmental milieu for such mixing may be localized, as evident in the mineral precipitation of ‘black smoker’ plumes, or can occur over broad scales, such as within fractures and pore spaces of the oceanic crust. Recent studies indicate that the thermal and chemical gradients created by such mixing can support rich and diverse microbial communities. Although access to these subseafloor habitats has commonly proven difficult, “windows into the subsurface” can easily be obtained through sampling of hydrothermal vent chimneys, where both chemical and thermal gradients are highly compressed. Over the past several years we have systematically documented the abundance and distribution of microorganisms within active and extinct sulfide chimney structures from the Juan de Fuca Ridge and the Southern East Pacific Rise (17-21 S). A range of venting styles and chimney types were sampled and corollary environmental data were carefully catalogued. The architecture of attached microbial communities within pore spaces was also characterized at microscopic scales. Co-variance analysis of the resulting data sets was employed to examine relationships between environmental and biological factors in vent chimney ecosystems. Initial results of this study indicate that the size of chimney structures (and subsequently microbial habitats) control microbial population densities. Co-variance analysis of venting temperatures show that large, high-temperature chimneys harbor the highest and most heterogeneous local population densities. Large, moderate temperature, diffuse chimneys harbor the highest overall populations. The lowest biomass was detected in interior zones of hot sulfide chimneys, in thin spires, and in porous beehive chimneys. Attached microbial communities are most pervasive and diverse in regions interior to chimney structures, where mineralogy indicates mixing of hydrothermal fluids and seawater. The integrated approach employed in this study begins to elucidate what factors control microbial abundance and distribution within rock-hosted hydrothermal ecosystems in the deep-sea.