THE HYDROLOGIC RESPONSE OF DESERT WETLANDS TO ABRUPT CLIMATE CHANGE IN THE SOUTHERN GREAT BASIN AND MOJAVE DESERTS

Desert wetlands are critical arid land ecosystems preserved in the geologic record as groundwater discharge (GWD) deposits. GWD deposits have proved useful in understanding the magnitude and timing of hydrologic change at glacial to interglacial timescales, but their inherently discontinuous nature, complex stratigraphy, and lack of temporal control have prevented query as to how desert wetlands responded to past rapid climate change. In the Las Vegas Valley, through stratigraphic analysis, geologic mapping and targeted dating, we have established a detailed lithostratigraphic and geochronologic framework for GWD deposits there that span 250 – 8.5 ka. With a highly resolved chronology over the last 35 ka, based on radiocarbon dating of charcoal and luminescence dating of sediments, our results show that GWD deposits in the Las Vegas Valley record dramatic hydrologic changes in response to abrupt climate oscillations during the late Quaternary, including the repeated growth and collapse of entire wetland systems. The hydrologic response of the Las Vegas paleowetlands demonstrates a tight correlation with Greenland/North Atlantic climate proxy data on millennial and submillennial scales, the first GWD-based hydrologic record to do so. GWD deposits are fairly common throughout the Mojave Desert and southern Great Basin. We are able to recognize the stratigraphic and lithologic changes first recognized in the Las Vegas Valley at multiple sites throughout the region. Coupled with stringent chronologic control, this recognition allows correlation of mappable members and beds of the newly defined Las Vegas Formation over a large geographic region and reveal that wetland ecosystems and their resultant deposits exhibited the same hydrologic responses to climate change over the past 150 ka, in synchrony, as those documented in the Las Vegas Valley. These results confirm that the record in the Las Vegas Valley is not simply reflecting local hydrologic conditions; rather, they are documenting changes in synoptic-scale climate patterns that operated over this region during the late Quaternary.