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Geology; December 2006; v. 34; no. 12; p. 993-996; DOI: 10.1130/G22810A.1
© 2006 Geological Society of America
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Mid-Holocene El Niño–Southern Oscillation (ENSO) attenuation revealed by individual foraminifera in eastern tropical Pacific sediments

Athanasios Koutavas*,1, Peter B. deMenocal2, George C. Olive3 and Jean Lynch-Stieglitz4

1 Department of Engineering Science and Physics, College of Staten Island, The City University of New York, 2800 Victory Blvd., Staten Island, New York 10314, USA, and Lamont-Doherty Earth Observatory of Columbia University, 61 Rt. 9W, Palisades, New York 10964, USA
2 Lamont-Doherty Earth Observatory of Columbia University, 61 Rt. 9W, Palisades, New York 10964, USA
3 Columbia University, 2960 Broadway, New York, New York 10027, USA
4 School of Earth and Atmospheric Sciences, 311 Ferst Drive, Georgia Institute of Technology, Atlanta, Georgia 30332, USA

Holocene reconstructions of the El Niño–Southern Oscillation (ENSO) provide valuable perspective on its recent evolution and can be important for assessing its future. Optimal assessment of past ENSO variability requires observations from its center of action in the eastern equatorial Pacific, but these are limited due to paucity of high-resolution paleoceanographic archives (e.g., corals). Here we use a new approach to quantify past ENSO variance based on the oxygen isotopic composition ({delta}18O) of individual foraminifera (Globigerinoides ruber) from deep-sea sediments in the ENSO source region. Individual G. ruber foraminifera behave as monthly recorders of sea-surface conditions, including ENSO extremes, circumventing the lack of annual resolution in the sediments. Intrapopulation {delta}18O distributions derived with this method from a core near the Galapagos Islands reveal mid-Holocene reductions in variance of 50%, requiring drastic attenuation of the ENSO amplitude. Furthermore, Mg/Ca thermometry indicates that mid- Holocene background conditions were accompanied by a stronger zonal temperature gradient that coincided with a northward- displaced Intertropical Convergence Zone (ITCZ). The results suggest that the position of the ITCZ is an important factor in the low-frequency modulation of ENSO and could influence its future evolution.

Key Words: Holocene ENSO • ITCZ • tropical Pacific • individual G. ruber • oxygen isotopes




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