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 improve isotopic measurements, as well as elucidate the fundamental behavior of isotopes, including their distribution, transport, and possible fractionation within and between Earth’s biogeochemical reservoirs. Of prime interest is isotopically tracking the flow, transformation, and distribution of carbon during natural and anthropogenic 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 understand the causes and consequences of climate change. To this end, we study carbon cycle dynamics in locations throughout the globe, from pristine natural settings to urban centers.


Current projects:


  1. Basic science investigations concerning the behavior of Ca and Sr isotopes during water-rock interactions and biological utilization.

  2. Using Ca and Sr isotopes to probe the relationship between chemical weathering and long-term climate change (New Zealand Southern Alps; Fiordland New Zealand; Iceland).

  3. Reconstructing the marine Ca and Sr cycles during carbon cycle perturbations and mass extinctions in “deep time” (Frasnian-Famennian boundary, Permo-Triassic boundary, Paleocene Eocene Thermal Maximum, Ocean Anoxic Events 1a and 2).

  4. Linkages between microbial activity, chemical weathering, and carbon cycling at the margin of the Greenland Ice Sheet (Russell Glacier, Kangerlussuaq, Greenland).

  5. 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).

  6. Isotopic tracking of river runoff and water mass mixing in the Arctic Ocean (Canadian Archipelago).

  7. Reactive transport modeling of chemical weathering and atmospheric CO2 consumption during regolith development.

  8. Rates and mechanisms of microbially-mediated rock weathering and their implications for the chemical evolution of Earth’s atmosphere and hydrosphere.

  9. Application of isotope tracers (B, Ca,and Sr) to the study of water-rock interactions in aquifers (Madison Aquifer, South Dakota; Wyodak-Anderson Coal Bed Aquifer, Wyoming).

  10. The “urban metabolism” of Chicago: the concentration and carbon isotope composition of atmospheric CO2.

Andrew D. Jacobson

Associate Professor • Department of Earth and Planetary Sciences • Northwestern University