nai

Project Progress

The convergence of two very disparate streams of data from natural systems promises new advances in the understanding of biological systems in hydrothermal environments. On the one hand, genomic data from thermophilic microbes are revealing complex histories of evolutionary speciation, presumably in response to environmental driving forces. On the other hand, new measurements and models of hydrothermal ecosystems from a geochemical perspective provide clues to the fluxes of energy, nutrients, and gradients that constitute habitats. There is enormous research potential in the merger of these diverse lines of evidence, which will engender new ideas about the mechanisms of evolution and the geochemical preservation of evolutionary history in the geologic record.

Work in Shock’s group continued on the quantitative geochemical bioenergetics of hydrothermal ecosystems. Field measurements on continental volcanic-hosted systems at Yellowstone, together with subsequent lab analyses, have allowed them to quantify the major and minor sources of geochemical energy in these systems and determine how they vary with composition. Variations in absolute and relative energy supplies disclose the underlying geochemical foundation for each hot-spring ecosystem. They have used these structures to prepare geochemically designed growth media, resulting in many new microbial cultures and considerable success in obtaining novel microbial isolates. Experiments on these isolates, couched in terms of their geochemical context, are revealing the role that each isolate plays in its hydrothermal ecosystem.

The group also continued applying mass transfer calculations to evaluate the geochemical composition of the ocean on Jupiter’s moon Europa. These calculations help constrain the speciation of major ions and the oxidation state of oceanic water on Europa, with consequences for the composition of underlying rocky material. They can also help identify histories that lead plausibly to the present state. Observational, geochemical, and cosmochemical data indicate that Europa has an oxidized Fe-metal-free mantle and an oxidized ocean rich in sulfate and carbonate ions. Model calculations show that the most effective way to generate a sulfate-rich ocean is cooling of hydrothermal fluids resulting from alteration of sulfide-bearing silicate rocks in Europa’s mantle. Our work demonstrates that present-day sulfate-rich cold oceanic water is in chemical disequilibrium with igneous rocks, if they are exposed at the oceanic floor. It follows that there are sources of geochemical energy that can support life in the vicinity of the oceanic floor on Europa, and that hydrothermal activity is not required to support life on Europa.