Welcome, and thanks for visiting our website!
The members of SesameLab are biogeochemists investigating the chemistry of metals (mostly in dissolved form) in the earth's lithosphere, hydrosphere, and biosphere. We are interested in understanding what reactions, both biological and abiotic, govern the distribution and activity of metals on earth in the present, in the past, and in the near future. Metals can be critical nutrients, toxic contaminants, valuable resources, or useful tracers of ancient biological activity and environmental conditions, and we're interested in advancing fundamental understanding of how metals play these various roles on our planet. In particular many of the questions we are currently addressing involve ancient history of metal cycling in the earth's oceans or environmental mobility of toxic metals in modern settings.
Although not all of us focus on metal isotopes, one of our main tools is the variation in ratios of heavy and light isotopes of transition and post-transition metals, such as Fe, Mo, Cd, Ni, and U. The ratios of heavy to light isotopes vary in nature (and in laboratory experiments) due to differential behavior of atoms with slightly different masses during chemical reactions. The result is that some reactions leave behind characteristic isotopic signatures in their products that can be preserved in rocks, bodies of water, or organic matter as tracers of what reactions have affected the metal inventory there.
For metals, the isotopic variations observed in nature are slight; it has only been possible to resolve them analytically since the late 1990s. Analysis is rapidly becoming routine with the spread of multiple-collector ICP mass spectrometers. Please click on the Lab section of this website for more information about the particular instruments we installed in 2012 for our own metal concentration and isotope measurements.
Many of our current projects are fundamental, experimental investigations of the reactions that cause isotope ratios to vary (or fractionate), conducted in simple systems with well-controlled conditions, for the following reason: The number of published metal isotope analyses on natural samples from all sorts of environments is burgeoning rapidly, and the prospect of how much scientists will learn from characterizing and interpreting metal isotope variations in nature is exciting. Few investigators, however, have yet attempted to elucidate the mechanisms that drive metal isotope fractionation. Without careful investigation of molecular-scale mechanisms and systematics of metal isotope effects, we cannot hope to interpret robustly the wealth of information available in natural samples. Thus, SesameLab scientists aim to integrate analysis of isotope systematics with molecular-scale characterization of metal species and reactions in our samples in order to provide critical groundwork for interpretation of metal cycling near the surface of the earth. Please click on the Research tab on this website for summaries of funded work currently underway.