DYNAMIC RESPONSE OF DESERT WETLANDS TO ABRUPT CLIMATE CHANGE

Paleoclimate proxy datasets from the American Southwest have established atmospheric teleconnections of past stadial/interstadial fluctuations with northern hemispheric climatic data. However, the types of records typically available (pluvial lakes, speleothems, packrat middens) and the general paucity of high-resolution studies have limited our understanding of past ecosystem and/or faunal response to rapid climate change. Wetlands in modern desert environments respond to climatic perturbations. In this study, groundwater discharge deposits (paleowetlands) were employed as a paleoclimate proxy, and underscore the vulnerability of modern spring habitats to changes in climate by documenting the rapid cessation of discharge associated with abrupt climatic warming, and the subsequent collapse of the wetland environments, repeatedly, over the last glacial period. Within the remarkably continuous, fossil-bearing late Pleistocene to Holocene desert wetland deposits of the upper Las Vegas Wash, in southern Nevada, we have established a comprehensive record of groundwater discharge deposits, demonstrating a tight correlation with Greenland/North Atlantic climate proxy data on a sub-millennial scale. The nature of hydrologic response is verified both temporally at high resolution for the last 50 ka as well as stratigraphically and sedimentologically, by recognition of episodes of groundwater discharge during wet/cool times, punctuated by abrupt, relatively brief periods of aridity as evidenced by soil formation, desiccation and erosion associated with warm/dry cycles. This dynamic response bears striking similarly with the established chronology of the Dansgaard-Oeschger and Heinrich events in the Greenland and North Atlantic ice core and marine records. We establish that desert wetlands, as a hydrologic system, and their inset vertebrate faunas, can now be utilized to query regional climate, ecosystem and faunal responses to abrupt, sub-millennial scale shifts in global climate and can be investigated by detailed chrono-stratigraphic analysis, δ¹⁸ O and δ¹³ C of fossil tooth enamel, paleoclimate modeling, and faunal analysis.