Hydrogen Isotope

Hydrogen has two stable isotopes: protium and deuterium. The relative amounts of these two isotopes vary widely in different organic materials as a result of natural processes that cause isotopic fractionation. Only recently have we been able to measure such differences in individual organic compounds. We do this by coupling a standard gas chromatograph to a specialized isotope-ratio mass spectrometer via a pyrolysis interface, such as in the Delta+XP system in our lab.

The ultimate goal is to use hydrogen isotopes in ancient organic molecules (molecular fossils) to understand more about environmental conditions throughout geologic history. This idea is nicely summarized in a paper by my colleague Peter Sauer. To do so, we first need to understand a wide array of processes that can influence the isotopic composition of molecules. These include 1) biological processes, especially the biosynthesis of molecules, 2) chemical processes that lead to hydrogen exchange between organic molecules and water, and 3) geochemical processes such as diagenesis that can alter both the structure and the isotopic composition of these molecules over very long periods of time. We are also interested in documenting the range of deuterium contents of natural organic materials, including lipids, petroleum, atmospheric aerosols, and anthropogenic pollutants.

To this end, we recently participated in a 10-day research cruise aboard the R/V New Horizon (June 20-30, 2004) in collaboration with David Valentine and his crew from Santa Barbara. We visited a total of 5 stations in the Santa Barbara Basin, Santa Monica Basin, and Gulf of Santa Catalina. Shipboard analyses documented oxygen concentration, dissolved gases (including H2 and CH4), porewater sulfate and sulfide, and organic acid concentrations. In addition, we brought back 6 coolers full of sediment cores, porewaters, seawater particulates (on filters), and seawater, all of which will be subjected to a suite of laboratory analyses. The goal is to document, for the first time, changes in the hydrogen-isotopic composition of organic materials throughout the carbon cycle of an anoxic basin. There are some great opportunities for undergraduate and graduate students here. Photos from the cruise - including the requisite sunset shots - are posted here. Thanks to Captain Murray Stein, restek Jeff Ravenhill, and the crew of the New Horizon for a fun and successful trip!