Ariel Anbar's research as part of the MIT/Harvard NAI Team focuses primarily on improving our understanding of atmosphere/ocean redox evolution and its effect on the biosphere (and vice-versa).

Multiple lines of evidence now point to a dramatic rise in atmospheric O₂ ~ 2200 million years ago. However, the change in redox state of the contemporaneous oceans is not well understood. While it is generally assumed that the oceans became more oxidizing in parallel to the atmosphere, recent data point to a very different scenario: The deep ocean may have become euxinic (anoxic and sulfide-rich) as the atmosphere became more oxidizing. In collaboration with Team member Andrew Knoll (Harvard), Anbar has considered the implications of this alternative scenario for the availability of redox-sensitive bioessential trace nutrients, such as Fe and Mo. These implications can explain the evolutionary pattern eukaryotes, as well as the unusual carbon isotope record of mid-Proterozoic carbonates (~ 1800 - 800 Ma).

For more on this topic, see:
A. D. Anbar and A. H. Knoll (2002). Proterozoic ocean chemistry and evolution: A bioinorganic bridge? Science 297, 1137-1142.

Because of the importance of this question, there is a need for geochemical tools to probe the redox condition of ancient oceans. Existing tools primarily provide information about redox conditions on the scale of individual basins. While useful, such information does not directly tell us about ocean chemistry on regional or global scales. Anbar and his group at the University of Rochester are developing a new geochemical approaching, using extremely precise measurements of the stable isotope composition of Mo, to solve this problem. This research makes use of state-of-the-art mass spectrometric methods developed in the Anbar group. The basis of this research is that finding that Mo isotope are fractionated during removal to Mn-oxides, but not during removal to euxinic sediments. Because these are the two main sinks of Mo from the oceans, the isotopic composition of Mo in seawater should covary with changes in the relative proportions of these sinks. An ocean Mo isotope paleorecord may be contained in black shales. This research is being pursued in collaboration with Andrew Knoll, Heinrich Holland and Yanan Shen at Harvard, and with Tim Lyons of the University of Missouri and the PSU NAI Team.

For more on this topic, see:
J. Barling and A. D. Anbar (2003). Mo isotope fractionation during adsorption to Mn-oxides. Earth Planet. Sci. Lett., submitted

J. Barling, G. L. Arnold and A. D. Anbar (2001). Natural mass-dependent variation in the isotopic composition of molybdenum. Earth Planet. Sci. Lett. 193, 447-457

A. D. Anbar, K. A. Knab and J. Barling (2001). Precise determination of mass-dependent variations in the isotopic composition of Mo using MC-ICP-MS. Anal. Chem. 73: 1425-1431.

Anbar's research is broadly aimed at unraveling the coevolutionary history of the Earth and its biota. Because of the potential importance of atmospheric O₃ (and hence O₂) as a "biosignature", this research also aims to improve strategies that will be used by the Terrestrial Planet Finder (TPF) mission in the search for life on extra-solar planets.