The people in my laboratory study (1) the processes of ecosystem carbon and nitrogen cycling, (2) environmental and ecological conditions of the past, and (3) ways of developing improved means of dating soils and landscapes, using a combination of stable and radiogenic isotope geochemistry.
We are actively engaged in better understanding the climatic and geological controls on the rates of carbon and nitrogen cycling in soils from around the world and the way in which soils serve as an important control on the chemical composition of the atmosphere. We have been using natural levels of 14C in soil organic matter to understand how climate and soil age control natural rates of carbon cycling in soils from a wide spectrum of field settings. We have examined how agriculture and forestry alter these rates of cycling. We are studying how the natural abundances of 18O/16O in soil CO2 may help to better serve as a tool in understanding the rates of sources and sinks to the atmospheric CO2 budget.
For more than a decade, we have been examining the way in which the isotopic composition of soils reflects climate and vegetation. Using ratios of stable carbon (13C/12C), nitrogen (15N/14N), and oxygen (18O/16O). We have shown that soil organic matter and calcium carbonate can reflect important characteristics about vegetation and climatic patterns. We, and others, have used these relationships to learn more about past climates using paleosols (soils that have been buried and preserved in sedimentary rock). Our research has extended to include fossil plants, in order to learn more about how physiological processes in plants record information about climatic conditions through variations in isotopic ratios in their tissues. We are also investigating the isotopic composition of modern and fossil animals as a means of determining their diet and environmental conditions.
Current Field Projects:, , Atacama Desert, Chile: We are collaborating with NASA investigators to study the biology and chemistry of soils in extreme environments, to better understand (through earth analogues) the past (or present) biogeochemistry of Mars.
Great Valley and Sierra Nevada, California: We are currently studying the rates of carbon and nitrogen cycling in soils that range in age from about 1,000 to 3,000,000 years in the Great Valley of California, and along elevation (climate) gradients of the western slope of the Sierra Nevada.
Wind River Basin, Wyoming: We are collaborating with colleagues from UC Santa Barbara and the Berkeley Geochronology Institute to develop U/Th isotope techniques to date the soils and landscapes of the Wind.
River Basin. We are also developing a long term paleoclimate perspective through a combination of dating and stable isotope analyses.
Central California Coast Range: We are collaborating with colleagues at UC Berkeley and Dartmouth College to link geomorphic modeling to soil C processes in steeply sloping watersheds of the Coast Range.
Western Oregon and New Mexico: We are studying the isotopic composition of the diet of feral horse herds in these states to better determine how the isotope composition of fossil horse tooth enamel may be used as a paleoclimate and diet indicator.
In the News
Scientists have found a new way to tease out signals about Earth’s climatic past from soil deposits on gravel and pebbles, adding an unprecedented level of detail to the existing paleoclimate record and revealing a time in North America’s past when summers were wetter than normal.
Steadily and alarmingly, humans have been depleting Earth’s soil resources faster than the nutrients can be replenished. If this trajectory does not change, soil erosion, combined with the effects of climate change, will present a huge risk to global food security over the next century.