HR: 13:55h
AN: PP33C-02 INVITED    [Abstracts]
TI: El Nino Variability During the Holocene: Constraints From Individual Foraminifera
AU: * Koutavas, A
EM: koutavas@mail.csi.cuny.edu
AF: College of Staten Island, City University of New York, 2800 Victory Blvd, Staten Island, NY 10314, United States
AB: Interpretation of tropical hydrologic anomalies in paleoclimate records requires careful consideration of variability in the El Niño-Southern Oscillation (ENSO), as the latter interacts strongly with key hydrologic systems such as the monsoons and the Intertropical Convergence Zone (ITCZ). Here we present new insights into the Holocene evolution of ENSO from oxygen isotope distributions of individual G. ruber foraminifera from sediment core V21-30 south of the Galapagos Islands, in the heart of maximum ENSO activity. Several hundred δ¹⁸O analyses of individuals have been carried out in the Holocene section of the core, with more in progress. Our main findings are summarized as follows: All indicators of oxygen isotopic variance reveal a progressive increase in ocean variability at the core site since the middle Holocene with minimum variance present ~6 ky BP. The decrease in mid-Holocene variance is primarily driven by reduced frequency of extreme values associated with El Niño and La Niña events. We estimate that the mid-Holocene frequency of El Niño events was reduced by a factor of 4-5, and that of La Niña events by a factor of 2-3. The δ¹⁸O distribution shapes further suggest that the seasonal cycle of SST which is presently very strong, was weaker in the mid-Holocene, a plausible consequence of the altered seasonal insolation due to precession. The interaction of ENSO with the seasonal cycle is today a key element of interannual ocean-atmosphere dynamics in the tropical Pacific, and our results suggest that such a link has also been important in the longer Holocene evolution of the ENSO system. The results are further examined in the wider context of Holocene climate adjustments in the tropical Pacific region involving the Walker circulation, the East Asian Monsoon and the ITCZ.
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4922 El Nino (4522)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting