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

^{1 1}School of Geography and Geosciences, University of St. Andrews, St. Andrews, Fife KY8 6AA, Scotland
^{2 2}Saskatchewan Isotope Laboratory, Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, Saskatchewan S7N 5E2, Canada
^{3 3}Keck Science Center, The Claremont Colleges, 925 North Mills Avenue, Claremont, California 91711, USA
^{4 4}Environment Canada, 11 Innovation Boulevard, Saskatoon, Saskatchewan S7N 3H5, Canada
^{5 5}Rafter Radiocarbon, National Isotope Centre, GNS Science, P.O. Box 31 312, Gracefield, Lower Hutt, New Zealand

We inferred climate change through the Pleistocene-Holocene transition from ¹³C and D values of bat guano deposited from 14.5 to 6.5 ka (calendar ka) in Bat Cave, Grand Canyon, Arizona. The ¹³C and 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, ¹³C values decreased, whereas 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 ¹³C and D values decreased. The ¹³C 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.

Key Words: arid • precipitation • vegetation • paleoclimate • North American Monsoon