Committee ChairCole, Julia E.
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PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractIn the semi-arid southwestern US, the lack of continuous records of climate over the last glacial cycle has precluded a complete understanding of the rates and timing of past regional changes in climate. Speleothems can provide high-resolution, continuous record of moisture, temperature, and, potentially, vegetation variations and can be precisely dated by uranium-series disequilibrium. We have produced two U-series dated speleothem δ¹⁸O records from Cave of the Bells (COB). COB is located in Santa Cruz County, Arizona on the east side of the Santa Rita Mountains (31°45'N, 110°45'W; 1700 m). The glacial speleothem δ¹⁸O record (53 to 8.5 ka) confirms that deglaciation in the Southwest proceeded via a stepwise shift, mirroring the Bølling-Allerød warming and Younger Dryas cooling, beginning around 15 ka. There is no evidence of early warming before the decline of the large ice sheets. In Marine Isotope Stage 3 (MIS3; 53 to 30 ka), we observe millennial variations similar to Dansgaard-Oeschger (DO) events first seen in Greenland ice core δ¹⁸O records with wet/cold conditions indicated by our cave record during glacial stadials (cold periods) and dry/warm during glacial interstadials (warmer periods). High-resolution U-series dating allows for refinement of the timing of DO events in MIS3, and spectral analysis confirms the presence of a 1515-year climate cycle during this time. The δ¹⁸O data from a Holocene stalagmite (~6.9 to 3.5 ka) average ~3‰ higher than modern and exhibit substantial multidecadal to multicentury variation. We propose that in addition to drier/warmer conditions in the winter, a stronger summer monsoon and perhaps warmer summer temperatures supplied waters with higher δ¹⁸O values to the cave during the mid-Holocene. Spectral analysis of early part of the δ¹⁸O record reveals variability at periods of 233 years and at 142 and 52. After ~4.9 ka a prominent shift from centennial to multidecadal periods of variability (a 70 to 50-year cycle) is observed and there is a slight decrease in average δ¹⁸O values. This shift is coincident with a hypothesized increase in El Niño activity, which is correlated to wet winters in the modern southwest, in the tropical Pacific at ~5 ka.