A 12,000 kyr paleohydroclimate record in the southeastern, U.S.A based on deuterium from bat guano

摘要

The southeastern United States endures environmental change from human population increase, climate change, and land-use alterations creating the need to understand baseline conditions and environmental patterns prior to human impacts. While paleoenvironmental data can be reconstructed from a variety of archives (e.g., lake sediments, tree rings, speleothems), some geographic areas contain fewer such records. One archive capable of recording moisture regimes and other paleoenvironmental changes over millennia but has received little attention relative to other climate proxies is bat guano deposits in cave systems. Bat guano deposits are found in many cave environments in the southeastern United States and can be used as an archive of paleoenvironmental data including precipitation, vegetation, and aspects associated with the ecology of bats. Here, we present a 12,000-year record of paleoenvironmental change based on delta H-2 stable isotopes in a guano core collected from Cave Springs Cave in Alabama, USA. Results suggest distinct shifts in moisture with dryer conditions during the early Holocene/late Pleistocene (12,200-9500 cal year BP) (delta H-2 values - 86.82 to --77.70), wetter conditions during the middle Holocene (9300-3900 cal year BP) (delta H-2 values - 125.74 to - 80.63), roughly coinciding with the Holocene Climatic Optimum event time interval (9000-5000 cal year BP). During the last 4000 years, conditions in the region shifted in the southeastern United States region becoming dryer once again. Climate inferences based on guano delta H-2 are consistent with the role of atmospheric moisture on regional vegetation changes suggested by previous pollen records obtained from lake sediment cores. This study suggests bat guano delta H-2 may be a reliable method to provide a long-term paleoclimate record.