Terrestrial carbonates – limestones that form in lakes, wetlands, soils, and caves – and the stable isotope geochemistry (δ13C, δ18O, Δ47, and Δ17O) records derived from them are used to study past climates, environments, and ecologies. However, many questions remain about what controls the style and timing of precipitation of different types of terrestrial carbonates. In particular, carbonates that form in wetland (i.e., palustrine) environments have been notably understudied in comparison to their soil and lake counterparts. 

I aim to better understand how stable isotope geochemistry records reflect drivers of formation and post-depositional processes across heterogeneous wetland landscapes. I do this through study of both present-day and ancient wetland ecosystems using carbonate sedimentology, in-situ environmental monitoring, and clumped and triple oxygen isotope geochemistry (AGU 2023 Invited Talk). 

Active field sites: Cariboo Plateau, BC and Las Tablas de Daimiel, Spain

Funding: 

• NSF Geobiology & Low-Temperature Geochemistry award#: 2244707 to M. Ingalls (Penn State), 2023. A dual clumped isotope approach to characterize disequilibrium in terrestrial carbonates. 

• NSF GRFP to A. Fetrow, 2018. What can wetland limestones tell us about past climates? A modern calibration study of palustrine carbonates using clumped isotope thermometry and the implications for paleoclimate research.

I am using triple oxygen and clumped isotopes to better quantify evaporation from Mono Lake in eastern California. A major goal of this research is to use geochemical data and hydrologic modeling to assist with water management and conservation strategies in the face of a rapidly changing climate. 

This project aims to more directly connect our understanding of the modern hydrologic system to changes in the regional hydroclimate in the recent geologic past. To do this, I am studying 1) the modern basin hydrology by sampling waters across the catchment (AGU 2023) and 2) recent paleoclimate history by comparing Common Era (last ~2000 years) lake sediment isotope records with historical accounts of environmental change in the region (AGU 2024). 

I am working as a part of a collaborative research team which includes members of the UM EARTH IsoPaleo Lab and SEAS Hydro research groups, and the Mono Lake Committee. Funding sources: NSF Postdoctoral Fellowship to ACF (EARPF #: 2204433) and UM Meet the Moment award.

I combined terrestrial sedimentology and carbonate clumped isotope geochemistry data from the mid-Cretaceous (ca. 113–89 Ma) Newark Canyon Formation, Nevada, to parse apart the effects of climate fluctuations and tectonic deformation (Fetrow et al., 2020). 

A key aspect of this research was to develop a more comprehensive framework for interpreting stable isotope geochemistry data from heterogeneous wetland carbonate deposits (Fetrow et al., 2022). 

With this record, we estimate that the Newark Canyon Fm. was deposited at low elevations (< 1.5km), implying that the development of a high elevation hinterland plateau (i.e., the “Nevadaplano”) was constrained to the Late Cretaceous (Fetrow et al., in prep; GSA 2022 Invited Talk). 

Upcoming Research:  Exploring the compounding role of heterogeneous mountainous landscapes and hothouse climates in promoting the development of modern terrestrial ecosystems — the so-called Cretaceous Terrestrial Revolution or ‘KTR’ — in North America.  This work is in collaboration with Dr. Luke Weaver (U. Michigan).

Beaver dam and pond along Provo River, Utah (PC: Tom Kelly 2012)

Beaver wetlands provide a wide range of ecosystem services, particularly in the Western US where water resources are limited. While there has been increased efforts to restore beavers to water-stressed landscapes to rebuild riparian ecosystems, some stakeholders remain concerned about excessive evaporative water loss from beaver ponds. Currently, there are no data that independently quantify evaporation and transpiration at beaver complexes or beaver mimicry sites. 

In collaboration with Dr. Rachel Havranek (University of Utah SRI Postdoctoral Fellow) and Dr. Emily Fairfax (Assistant Professor, University of Minnesota), we seek to better quantify how evaporative water loss is affected by the presence of beavers and beaver mimicry sites in alpine ecosystems. This study will begin to provide much-needed data to better inform water rights and water security discussions for beaver-related restoration efforts.

 Field work for this project will begin in summer 2025 focused on field sites in the Wasatch Range, Utah.

What environmental conditions allowed “giant” (<5 m) stromatolites to form repeatedly in the Laney Member of the Eocene Green River Fm?

Ingalls, M., Fetrow, A. C., Snell, K. E., Frantz, C. M., & Trower, E. J. (2022). Lake level controls the recurrence of giant stromatolite facies. Sedimentology, 1–26. doi.org/10.1111/sed.12967

Was it biotic or abiotic forces that caused the rise of the modern grassland ecosystem of the North American Great Plains?

Fox, D. L., Martin, R. A., Roepke, E., Fetrow, A. C., Fischer-Femal, B., Uno, K. T., et al. (2015). Biotic and Abiotic Forcing During the Transition to Modern Grassland Ecosystems: Evolutionary and Ecological Responses of Small Mammal Communities Over the Last 5 Million Years. The Paleontological Society Papers, 21, 197–218. doi.org/10.1017/s1089332600003016

Fetrow, A. 2015. Insights into the evolution of the Great Plains grassland ecosystem over the last 5 million years from paleotemperature and paleovegetation records. Honors Senior Thesis,  University of Puget Sound.