INFORMING MANAGEMENT OF DESERT WETLAND ECOSYSTEMS THROUGH STUDY OF THEIR PAST RESPONSE TO ABRUPT CLIMATE CHANGE

Springs and wetlands are ubiquitous features in the deserts of the American Southwest, and are keystone ecosystems that are home to thousands of threatened and endangered species. They are geographically distinct and hydrologically isolated, which creates significant challenges for their effective management. Of particular concern is how fast they might respond to changes in climate that are predicted for the future. Understanding how springs and desert wetlands responded to climatic events in the recent geologic past and defining the time scales on which the responses took place, therefore, can provide critical baseline information for use in management strategies. To this end, we have studied paleowetland deposits associated with one of the most preeminent examples of abrupt climate change, the Younger Dryas (YD) climate event, which began at 12.9 ka with the warm-to-cold onset occurring over just a few decades and the cold-to-warm termination at 11.7 ka taking place over decades to years. Paleowetland deposits that firmly date to the YD are present at sites throughout the Southwest, and can be dated accurately using radiocarbon dating of charcoal, organic-rich sediment, and gastropod shells. YD deposits exhibit a variety of lithologies that are determined by their geologic settings, hydrologic characteristics, and especially sedimentation rates, but each represents climatic conditions that were wetter/cooler than what prevailed both before and after. The spectacular and newly discovered YD-age deposits of the Rogers Beds in the northern part of Death Valley are especially noteworthy as they are nearly identical to some of the most highly resolved YD marine and lacustrine sediments in the North Atlantic. Overall, our studies have shown that (1) desert wetlands are extremely sensitive to climate change, (2) they respond to climatic perturbations faster than we can delineate with radiocarbon methods, and (3) once they dry up, they can remain absent from the landscape for decades to centuries, all of which have significant implications for management and preservation strategies in light of projected future warming.