HR: 11:50h
AN: U42B-07    [Abstracts]
TI: Holocene hydroclimate of the Sonoran desert: Results from Cave of the Bells, Arizona
AU: * Cole, J E
EM: jecole@email.arizona.edu
AF: Department of Geosciences, University of Arizona, 1040 E. 4th St, Tucson, AZ 85721, United States
AU: Wagner, J D
EM: jwagner@geo.arizona.edu
AF: Department of Geosciences, University of Arizona, 1040 E. 4th St, Tucson, AZ 85721, United States
AU: Beck, J W
EM: wbeck@physics.arizona.edu
AF: Department of Physics, University of Arizona, 1118 E 4th St., Tucson, AZ 85721, United States
AU: Patchett, P J
EM: patchett@email.arizona.edu
AF: Department of Geosciences, University of Arizona, 1040 E. 4th St, Tucson, AZ 85721, United States
AU: Henderson, G M
EM: Gideon.Henderson@earth.ox.ac.uk
AF: Department of Earth Sciences, Oxford University, Parks Road, Oxford, OX1 3PR, United Kingdom
AB: In the desert of North America, water availability fundamentally limits the scope of human and ecological activity. Understanding the natural variability of the region's hydroclimate and its sensitivity to radiative forcings is important for anticipating future changes in water availability. Here we present an isotopic record from a speleothem collected in southeastern Arizona that spans 3.5-6.9 ky BP at interannual resolution. Measurements on modern cave and meteoric waters suggest that the cave currently receives only winter moisture, despite the fact that half the region's precipitation falls during the summer monsoon. Speleothem isotopic values are higher than present by about 3 per mil, a change too large to be explained by warming/drying. We suggest this change is due to an increase in the amount of summer monsoon precipitation reaching the cave, consistent with orbital forcing of a stronger monsoon. The Holocene record of climate in the southwest US is complex, but many records support an intensified monsoon, and some suggest drying that is confined to winter. Our record is consistent with an increase of summer moisture relative to winter during the mid-Holocene, a scenario that explains a wide range of divergent paleoclimatic results. The record also shows substantial multidecade-century scale variability. Spectral analysis of discrete intervals reveals peaks in the early part of the record near 233 and 142 years, giving way to a broad concentration of multidecadal variance at periods between 50-70 years since 4.9 ky BP. The recent transition to higher frequency variability is consistent with the hypothesized evolution of ENSO towards more frequent occurrence. Our record clearly illustrates both the importance of multidecade-century time scales of hydroclimate variability and the sensitivity of the North American monsoon to radiative forcing. We hope to quantify monsoon changes by expanding our work into northern Mexico, where the summer monsoon dominates annual rainfall.
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1637 Regional climate change
DE: 1812 Drought
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4958 Speleothems
SC: Union [U]
MN: 2007 Joint Assembly