For the past several years a primary focus of my research has been the characterization and interpretation of O isotope fractionations in the PO4-water system during biogeochemical cycling of P in natural waters and sediments. A major area of current research surrounds characterization and "ground-truthing" of 18O/16O ratios ( 18O) signatu>es of phosphates in mid-ocean ridge (MOR) hydrothermal Fe-oxide deposits, with the goal of identifying reliable 18Op biosignatures and isotopic tracers of microbial activity and P cycling at MOR's, in Earth's deep biosphere, Mars and beyond. Many of the activities in my laboratory are devoted to development of methods for extraction and O isotopic analysis of PO4 (18O/16O and 17O/16O) in a range of geologic, biologic and extraterrestrial materials including deep-sea sediments, ancient rocks; biomass, and Martian soil analogue materials. A second area of major research is the O and S isotope behavior of sulfate during microbial S cycling in marine sediments (D'Hondt et al., 2004; Blake et al., 2005, Boettcher et al., 2005).

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