- My research interests revolve around the use of environmental stable isotope ratios. I supervise a laboratory for the analysis of stable isotope ratios of carbon, hydrogen, nitrogen, and oxygen. My specific areas of research include modeling the global carbon cycle using isotope ratios in atmospheric carbon dioxide and methane, development of techniques for measuring isotope ratios in atmospheric gases, reconstructions of paleo-environmental conditions using isotopes in ice cores, reconstructions of past environments from isotopes in organic materials, and tracing of ground water flow and recharge. I have been a member of several deep ice coring projects in Greenland and Antarctica. I am also an affiliate of NOAA and work closely with the Carbon Cycle Group there. My ice core research has helped to show that large climate changes can occur as abrupt and rapid shifts. My research in isotopes in the carbon cycle has helped to quantify atmospheric carbon dioxide uptake by land plants.