Mid-Holocene El Niño–Southern Oscillation (ENSO) attenuation revealed by individual foraminifera in eastern tropical Pacific sediments
- 1Department 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
- 2Lamont-Doherty Earth Observatory of Columbia University, 61 Rt. 9W, Palisades, New York 10964, USA
- 3Columbia University, 2960 Broadway, New York, New York 10027, USA
- 4School of Earth and Atmospheric Sciences, 311 Ferst Drive, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
Abstract
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 (δ18O) 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 δ18O 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.
Footnotes
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↵*koutavas{at}mail.csi.cuny.edu
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- Accepted 20 June 2006.
- Received 25 March 2006.
- Revision received 16 June 2006.
- The Geological Society of America, Inc.
