SUBMILLENNIAL-SCALE HYDROLOGIC CHANGES RECORDED IN LATE QUATERNARY WETLAND DEPOSITS IN THE SOUTHWESTERN U.S

Recent investigations have established that wetlands in the Las Vegas Valley (southern Nevada, USA) expanded and contracted during the late Quaternary in near lockstep with climate oscillations recorded in Greenland ice cores. The detailed chronologic and stratigraphic frameworks established in Las Vegas Valley provide a context for evaluating the response and sensitivity of similar systems elsewhere in the southern Great Basin and Mojave Deserts. One of the primary questions to be addressed is how fast these systems responded to past episodes of abrupt climate change. Wetland deposits dating to the Younger Dryas (YD) cold event are fairly common in the southwestern U.S. and present an opportunity to evaluate whether disparate watersheds responded in unison to changing climatic conditions toward the end of the Pleistocene. Using the Las Vegas Valley wetland record as the chronologic linchpin, we show that desert wetlands responded to the onset and termination of the YD at essentially the same time, at least within the limits of radiocarbon dating, over large areas of the southwestern U.S. Moreover, at sites with exceptionally high sedimentation rates, including Dove Spring and Mesquite Spring in southern California, we recognize intra-YD hydrologic changes in the wetland deposits, likely at centennial or possibly even finer timescales, which are not evident in most wetland sedimentary sequences. Together, these data add to the growing body of evidence that desert wetlands are exceptionally sensitive to climate change, show that they respond to climate perturbations on timescales relevant to society, and illustrate the extreme vulnerability of endemic flora and fauna that depend on these ecosystems to survive in arid landscapes.