HR: 12:05h
AN: GC32A-08    [Abstracts]
TI: Late Glacial to Early Holocene Climate Oscillations in the American Southwest
AU: * Cole, K L
EM: ken_cole@usgs.gov
AF: USGS Southwest Biological Science Center, Colorado Plateau Research Station, P.O. Box 5614, Northern Arizona University, Flagstaff, AZ 86011 United States
AB: The late Glacial to early Holocene climate shifts in American southwest between about 16 and 8 ka have often been depicted as a trend of increasing temperature and/or declining winter precipitation, usually with a sharp step change around 13 ka (11,000 yr B.P.) signaling the shift from Pleistocene to Holocene climates. But as paleoclimatic proxies are becoming increasingly sophisticated in their stratigraphic detail and dating resolution, a much more complex picture of these climatic changes is emerging. Compilation of data from multiple proxy sources suggest that not only are shifts in temperature and precipitation not concurrent, but shifts in summer vs. winter temperature and precipitation are also not necessarily concurrent. The maximum disparity between summer vs. winter solar insolation that developed during this period is probably responsible for some of these changes in seasonality. Proxy data from packrat middens suggest that although winter temperatures were only 4.5 to 6.5 ° C below modern during the Bolling/Allerod, these temperatures quickly shifted to 7.5 to 8.7 ° C below modern during the early Younger Dryas, only to rebound rapidly by at least 4 ° C between ca. 11.8 ka and 11.5 ka. Considering the error inherent in this radiocarbon chronology, the timing and rate of this rapid warming at the end of the Younger Dryas is indistinguishable to similar increases observed in the better-dated records from Greenland ice cores and Eastern Pacific ocean cores. Proxy records reflecting summer temperatures from high elevation fossil pollen data reflect similar changes but of much lower magnitude. Other proxy data from packrat middens using higher elevation species sensitive to precipitation changes suggest well developed monsoonal precipitation occurred during the Bolling/Allerod through the early Holocene. This interpretation is supported by other proxy data as disparate as isotopic studies from New Mexico and soil development series from the Mojave Desert. Although all of these climate shifts are complex and in need of much more detailed study, the traditional scenario of the winter rainfall regime Pleistocene suddenly yielding to warmer temperatures and summer precipitation at 13 ka is not supported.
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 3344 Paleoclimatology (0473, 4900)
SC: Global Climate Change [GC]
MN: Fall Meeting 2005