Digging into Soil Carbonate Formation Processes with Triple Oxygen Isotopes

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).

Drylands are water-limited ecosystems that cover 40% of Earth's land surface, are home to > 2.5 billion people, and are particularly vulnerable to climate change. Carbonate-forming soils, which are common in dryland ecosystems, are important components to the carbon cycle and critical for building records of past climate, but we do not fully understand how they form.

This project will investigate the role of water loss from soils as a mechanism for soil carbonate formation. The team will use the three stable isotopes of oxygen, 16O, 17O and 18O, to distinguish between the role of soil water loss via evaporation vs. uptake by plants. While ratios of oxygen isotopes 18O to 16O are commonly used to study soil carbonate and other climate archives, 17O, the 3rd stable oxygen isotope, is far less abundant and has not been fully developed for studies of soils and past climate.

This project will develop triple oxygen isotope distributions (comparing all three oxygen isotopes) as tools for investigating soil formation processes in modern and ancient climates through field work across major ecological and aridity gradients in the U.S., including sites in the Drylands Critical Zone Network. The results from this work will improve reconstructions of past climate, with particular attention to detecting drought and aridity in ancient ecosystems.

The project will provide training for a postdoctoral scientist in preparation for building her own analytically intensive laboratory and research program, filling the need for more laboratories and PIs who are capable of making analytically challenging triple oxygen isotope measurements. Training of undergraduates at three institutions will be integral to the field components to this research.

The undergraduate component to this work will broaden participation in the geosciences and include recruiting participants through the University of Michigan Earth Camp program.

Increased variability in the hydrologic cycle due to modern climate change will potentially lead to feedbacks in water and carbon storage. At the same time, modern climate change enhances the need for tools to identify water stress in ancient climates as analogues for our future world. This project uses triple oxygen isotopes to evaluate the role of evaporation and transpiration in soil dewatering during soil carbonate formation in the U.S.

This work will include a study of triple oxygen isotopes in carbonate in soils and in their parent meteoric waters. Our field work will focus on four sites in the US that include the hyper-arid Mojave Desert of California, the subhumid deciduous forest in Michigan, and two intermediate sites in arid environments, Reynolds Creek, Idaho and the Jornada Basin in New Mexico.

The outcomes of this work will include tools for stripping away the effects of evaporation on pedogenic carbonate delta 18O to reveal meteoric water delta 18O, which is the holy grail for paleohydrology and paleoaltimetry. This work will improve our understanding of how abiotic and biotic processes each control pedogenic carbonate formation; this understanding is necessary to be able to predict how and where pedogenic carbonate will precipitate in natural and agricultural soils under the predicted increased hydrological variability, with implications for carbon sequestration and water storage in dryland critical zones.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.