Stable carbon and hydrogen isotopes from bat guano in the Grand Canyon, USA, reveal Younger Dryas and 8.2 ka events

We inferred climate change through the Pleistocene-Holocene transition from δ13C and δD values of bat guano deposited from 14.5 to 6.5 ka (calendar ka) in Bat Cave, Grand Canyon, Arizona. The δ13C and δD values generally covaried, indicating that regional late Pleistocene climate was relatively cool and wet, and early Holocene climate gradually became warmer with increased summer precipitation until ca. 9 ka, at which time the onset of modern North American Monsoon–like conditions occurred. During the Younger Dryas event, δ13C values decreased, whereas δD values increased, indicating a cool and possibly drier period. We also observed a distinct isotopic anomaly during the 8.2 ka event, at which time both δ13C and δD values decreased. The δ13C values abruptly increased at 8.0 ka, suggesting a rapid change in atmospheric circulation and greater influence from convective storms originating from the south. Deposits of bat guano represent a largely untapped source of paleoenvironmental information that can provide continuous and long-term continental archives of environmental change