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Oceanic conditions in the eastern equatorial Pacific during the onset of ENSO in the Holocene

Published online by Cambridge University Press:  20 January 2017

Paul Loubere ,
Mathieu Richaud ,
Zhengyu Liu  and
Figen Mekik
Paul Loubere*
Affiliation:
Department of Geology and Environmental Geosciences, Northern Illinois University, DeKalb, IL 60115, USA
Mathieu Richaud
Affiliation:
Department of Geology and Environmental Geosciences, Northern Illinois University, DeKalb, IL 60115, USA
Zhengyu Liu
Affiliation:
Center for Climate Research, 1225 W. Dayton St., University of Wisconsin at Madison, Madison, WI 53706-1695, USA
Figen Mekik
Affiliation:
Department of Geology, Grand Valley State University, Allendale, MI 49401, USA
*
*Corresponding author.Email Address:[email protected] (P. Loubere)
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Abstract

Records from South America show that modern ENSO (El Nino-Southern Oscillation) did not exist 7000 cal yr B.P. and has developed progressively since then. There has been little information available on oceanic conditions in the eastern equatorial Pacific (EEP) to constrain explanations for ENSO onset. We report quantitative observations on thermocline and mixed-layer conditions in the EEP during ENSO start up. We found important changes in both the thermocline and the mixed layer, indicating increased upwelling of cooler waters since 7000 cal yr B.P. This resulted from change in the source and/or properties of waters supplying the Equatorial Undercurrent, which feeds upwelling along the equator and the Peru margin. Modeling shows that ENSO is sensitive to subsurface conditions in the eastern equatorial Pacific and that the changes in the thermocline we observed were driven by extratropical processes, giving these a role in conditioning the development of ENSO. This is in contrast to models that call for control of equatorial Pacific oceanography by tropical processes only. These infer stronger upwelling and cooler surface waters for the EEP during the mid-Holocene, which is not supported by our results.

Type
Research Article
Information
Quaternary Research , Volume 60 , Issue 2 , September 2003 , pp. 142 - 148
Copyright
University of Washington

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