Research

My students and I specialize in low-temperature aqueous and radiogenic isotope geochemistry. We combine fieldwork, laboratory experiments, and modeling to quantify chemical, physical, and biological phenomena that cycle elements and their isotopes at the Earth’s surface. Many activities use isotopes to probe the compositional evolution of the Earth, at timescales spanning the geological to modern-day. Other projects aim to elucidate the fundamental behavior of isotopes, including their distribution, transport, and possible fractionation within and between Earth’s biogeochemical reservoirs. A prime goal is to isotopically track the flow, transformation, and distribution of carbon during during gradual and catastrophic environmental change. Several investigations focus on mineral weathering and precipitation reactions that cycle carbon and other elements, link inorganic and organic aspects of the Earth system, and control the geochemistry of soils, rivers, aquifers, seawater, and the atmosphere. Related efforts seek to improve radiogenic isotope measurements by thermal ionization mass spectrometry. 

Current projects:

  • Using Ca and Sr isotopes to probe the relationship between chemical weathering and long-term climate change (New Zealand Southern Alps; Iceland; Oman)
  • Reconstructing the marine Ca and Sr cycles during C cycle perturbations and mass extinctions in “deep time” (Snowball Earth events, Permo-Triassic boundary, Cretaceous-Tertiary Boundary, Ocean Anoxic Events 1a and 2; Paleocene Eocene Thermal Maximum).
  • Linkages between microbial activity, chemical weathering, and C cycling at the margin of the Greenland Ice Sheet (Russell Glacier, Kangerlussuaq).
  • Isotopic tracking of river runoff and water-mass mixing in the Arctic Ocean (Canadian Archipelago).
  • Studies focusing on the elemental and isotope (Ca, Sr, and C) geochemistry of Alaskan rivers and soils with the aim of developing new proxies for tracking Arctic climate change, permafrost stability, and organic carbon export at the watershed scale (North Slope, Alaska).