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 delta C-13 and delta D values of bat guano deposited from 14.5 to 6.5 ka (calendar ka) in Bat Cave, Grand Canvon, Arizona. The delta C-13 and delta D 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, delta C-13 values decreased, whereas delta D 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 delta C-13 and delta D values decreased. The delta C-13 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.