HR: 13:55h
AN: PP53A-02 INVITED     [Abstracts]
TI: Persistence of ENSO-Like Climate Variability Throughout the Holocene
AU: * Asmerom, Y
EM: asmerom@unm.edu
AF: Dept. of Earth & Planetary Sciences, University of New Mexico 200 Yale Blvd., NE, Albuquerque, NM 87131 United States
AU: Polyak, V J
EM: polyak@unm.edu
AF: Dept. of Earth & Planetary Sciences, University of New Mexico 200 Yale Blvd., NE, Albuquerque, NM 87131 United States
AU: Rasmussen, J B
EM: jbtoledo@unm.edu
AF: Dept. of Earth & Planetary Sciences, University of New Mexico 200 Yale Blvd., NE, Albuquerque, NM 87131 United States
AU: Burns, S J
EM: sburns@geo.umass.edu
AF: Dept. of Geosciences, University of Massachusetts Amherst, 233 Morrill Science Center , Amherst, MA 01003 United States
AU: Lachniet, M S
EM: matthew.lachniet@ccmail.nevada.edu
AF: Department of Geoscience Univ. of Nevada, Las Vegas, 4505 Maryland Parkway , Las Vegas, NV 89154 United States
AB: The El Ni¤o Southern Oscillation (ENSO) is a Pacific climate phenomenon with global climate teleconnections. Many aspects of the modern ENSO regime are unknown, and its persistence and modalities in the past are even less known. In continents, the main difficulty has been finding ENSO-sensitive proxies with near-annual resolution that are datable by isotopic techniques. Speleothems from ENSO-influenced regions, such as the Southwestern USA (SW), offer new opportunities. In the SW, El Ni¤o years are typically wetter and La Ni¤a years drier than normal. ENSO teleconnections with precipitation are especially strong when the SOI and NINO3 are out-of-phase during negative phases of the Pacific Decadal Oscillation (PDO) (1). Data from uranium-series dated late Holocene speleothems from southern New Mexico and an early Holocene-Pleistocene speleothem from the Grand Canyon (Arizona) are used to investigate ENSO variability during the Pleistocene-early Holocene as compared to the Late Holocene. It has been previously suggested that frequency and magnitude of ENSO has changed since the early Holocene (e.g. 2). Our data consist of growth thickness variations of annual bands for the late Holocene and gray scale and stable isotopic data for the early Holocene and the Pleistocene-Holocene transition. Previously we had demonstrated that growth thickness in our annually-banded speleothems is related to precipitation (3). Gray scale in our Grand Canyon speleothem is well-correlated with δ¹⁸O isotopic values (R = -0.63). Dark bands, which we interpret to represent arid years, correlate with high δ¹⁸O values. Multiple-taper spectral (MTM) and wavelet analyses of the late Holocene data show statistically significant (above 90% confidence) peaks at interannual (2-6 yr) timescales in addition to decadal and centennial frequencies throughout the record, which we suggest represent PDO and solar modulators. The prominent interannual frequencies in our datalikely reflect the persistence of a modern-style ENSO through the late Holocene. In contrast, results of spectral analyses of the late Pleistocene-early Holocene gray scale data show distinct changes in interannual variability, which correlate with centennial scale frequencies in dry-wet cycles that closely correspond to solar variability. During wet periods the interannual frequency is approximately 12 years, while during dry periods the frequency varies from 2 to 8 years, suggesting that the dry periods are characterized by more frequent La Nina events. The gray scale data might not record the occurrence of El Ni¤o events in the wet phases, although previously published lake data (e.g. 2), which are sensitive to El Ni¤o events in that they represent El Ni¤o-driven discharge events, suggest decreased ENSO activity prior to the late Holocene. Our speleothem data however suggest that high-frequency ENSO-like events have persisted throughout the Holocene, although early variability seems to show the dominance of La Ni¤a events. 1. McCabe and Dettinger, Int. J. Climatol. 19: 1399-1410 (1999). 2. Moy et al., Nature 420, 162-165 (2002). 3. Asmerom and Polyak, Quaternary Research 61: 119-121 (2004).
DE: 4922 El Nino (4522)
DE: 4924 Geochemical tracers
DE: 4954 Sea surface temperature
DE: 4958 Speleothems
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005