Collaborative Research: Late Quaternary Paleoenvironments of Cuatro Cienegas, Mexico, a Hotspot of Endemism in North America

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Sediments in lakes and wetlands preserve important evidence of changes in Earth's climate, vegetation, and ecological dynamics over the past 20,000 years. In this project, researchers will study sedimentary archives to document the ecological and environmental history of the Cuatro Ciénegas valley in the Chihuahuan desert of northern Mexico. Cuatro Ciénegas is home to a unique desert spring system that supports North America's highest concentration of endemic species, garnering comparisons to the Galapagos Islands. The high endemism of the Cuatro Ciénegas biota has been explained as a consequence of long-term isolation and environmental stability in the valley. A pollen record from a sediment core analyzed in the 1970s was originally interpreted as supporting this hypothesis, but recent reevaluation of the original record, along with new pollen data from a nearby packrat midden, challenged the assumption of long-term environmental stability within the valley. A complication with the old record is uncertainty over early radiocarbon dates on bulk sediment. This research project will make use of two new sediment cores that contain macrofossils suitable for AMS dating along with abundant pollen and charcoal that will provide information on both vegetation and fire history. The researchers will test the hypothesis of long-term stability in the Cuatro Ciénegas valley by documenting, with secure dating and at higher resolution, past environmental conditions in Cuatro Ciénegas. The cores were recovered in 2008 from wetlands in the Reserva Privada Pozas Azules, which contains a large assemblage of sinkhole ponds, or pozas, in various stages of succession. The 12.3 m profile from Poza Cortador spans over 14,000 years and shows evidence of succession from a deep-water poza to a marsh with emergent wetland vegetation. A profile from nearby Poza Tule covers the last c. 5000 years. Continuous depositional environments suitable for pollen preservation are exceptionally rare in the arid regions of North America. The sediment records to be analyzed will provide important evidence of Late Glacial and Holocene conditions in the Chihuahuan Desert and provide insight into the environmental changes that occurred outside of glaciated regions of North America. The Cuatro Ciénegas valley has become a natural laboratory for studying fundamental issues in biogeography, ecology, and evolution, and this research on long-term history will increase the value of this natural laboratory. The results of the research project will inform paleoclimatology and biogeography, and will provide crucial context for the many studies of speciation, coevolution, microbial evolution and astrobiology that focus on the unique species and species assemblages of the Cuatro Ciénegas valley. Project results will also inform ongoing efforts to manage, conserve, and restore the natural resources and endemic biodiversity of Cuatro Ciénegas. The research project will provide educational opportunities for several graduate and undergraduate students, and for K-12 students and others served by project outreach. This project is jointly supported by the Geography and Spatial Sciences Program and the Population and Community Ecology Program.