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Project Progress

The focus of this research is to determine if fractionations of transition metal isotopes can be used as biosignatures. We are also interested in the possible use of such fractionations to study changes in metal geochemical cycling, which could provide insight into environmental change and/or biochemical evolution. The latter applications are pursued jointly with the Harvard Team.

In Year 4, we continued examination of Fe isotopes and began examining biological effects on Mo isotopes.

Fe isotope efforts focused primarily on the study of isotope effects during mineral weathering, in collaboration with Prof. S. Brantley (PSU Team). We continue to find evidence that Fe isotopes are fractionated during leaching by biogenic ligands. This fractionation is larger than in the absence of strong Fe-chelating ligands. This suggests two things. First, Fe isotope fractionation by bacteria may occur primarily during Fe uptake. Second, siderophores may leave a uniquely biogenic “fingerprint” during weathering. We are exploring the latter possibility by examining the Fe isotope composition of paleosols, with a particular focus on the 2.7 Ga Mt. Roe paleosol sampled during the ’01 MtEE expedition (see below), in collaboration with R. Rye (University of Southern California (USC)). These Fe studies were conducted, in part, during evaluation of a “3^rd generation” MC-ICP-MS instrument at the ThermoFinnigan factory in Bremen, Germany.

Mo isotope efforts have focused mostly on paleoredox applications, primarily in our activities with the Harvard Team. However, we have also initiated studies (again, with Brantley’s group) of Mo isotope fractionation during mineral leaching. Intriguingly, fractionation in this system occurs during uptake of Mo into bacteria, but apparently not during leaching itself.