HR: 08:45h
AN: PP21A-02    [Abstracts]
TI: Causes for Large-Scale Precipitation Variability in the Southwestern USA During the Late Holocene
AU: * Rasmussen, J B
EM: jbtoledo@unm.edu
AF: Department of Earth and Planetary Sciences, Northrop Hall, MSC03-2040, University of New Mexico, Albuquerque, NM 87131 United States
AU: Polyak, V J
EM: polyak@unm.edu
AF: Department of Earth and Planetary Sciences, Northrop Hall, MSC03-2040, University of New Mexico, Albuquerque, NM 87131 United States
AU: Asmerom, Y
EM: asmerom@unm.edu
AF: Department of Earth and Planetary Sciences, Northrop Hall, MSC03-2040, University of New Mexico, Albuquerque, NM 87131 United States
AB: The continental climate variability of the late Holocene can be difficult to evaluate for lack of high-resolution, dateable proxies. We have compiled an annually resolved record of relative moisture for the last 3000 years using stalagmites in southeastern New Mexico. Stalagmite growth bands were combined with high-precision U-Th dates to develop the high-resolution record, with wetter periods indicated by intervals of thicker banding, and drier periods by thinner banding, hiatuses, and changes in mineralogy. Although the response of individual stalagmites to wet/dry events varies, comparisons to the regional instrumental precipitation and tree ring data confirm that the stalagmites reflect regional moisture variability. The compiled stalagmite record exhibits dramatic variability over the past 3000 years, motivating our study into what may be driving precipitation variability in the study region. We compared the modern instrumental precipitation record for the region with the Southern Oscillation Index (SOI) and Pacific Decadal Oscillation (PDO) Index and found significant correlation, suggesting the El Nino-Southern Oscillation (ENSO) and PDO are possible mechanisms for modulating past precipitation variability. To test this hypothesis, we conducted time series analyses on contemporaneous segments of two stalagmite records with no apparent hiatuses to assess any similarities in the spectral densities. Multiple-taper spectral analysis was used to test for significant narrowband or harmonic signals and wavelet analysis conducted to evaluate the amplitude and frequency modulation of the spectral peaks in the time series. Results show statistically significant peaks at both interannual (2-5 years) and decadal-scale (15-30, 40-50 years) frequencies. While interannual variability is present throughout the evolutive spectrum, it is the decadal-scale variability that coincides with major shifts and overall increases in precipitation in both records. Given the modern precipitation regime, it is likely the decadal events correspond to the PDO or a low-frequency component of ENSO (or ENSO-like mechanism). The timing of these peaks in the evolutive spectrum suggests that these mechanisms have been driving the moisture variability in the Southwest over the past 3000 years.
DE: 1040 Isotopic composition/chemistry
DE: 3344 Paleoclimatology
DE: 4215 Climate and interannual variability (3309)
DE: 4522 El Ni¤o
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2005 Joint Assembly