Figure 1. Paleoclimatic proxies from ODP Site 846.
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Evolution of the Eastern Tropical Pacific Through Plio-Pleistocene Glaciation
Science
Vol. 312, pp. 79-83, 7 April 2006.
Kira T. Lawrence, Zhonghui Liu, Timothy D. Herbert
Department of Geological Sciences, Brown University, Box
1846, Providence, RI 02912, USA.
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ABSTRACT:
A tropical Pacific climate state resembling that of a permanent El Nino
is hypothesized to have ended as a result of a reorganization of the ocean heat
budget ~3 million years ago, a time when large ice sheets appeared in the high
latitudes of the Northern Hemisphere. We report a high resolution alkenone
reconstruction of conditions in the heart of the eastern equatorial Pacific (EEP)
cold tongue that reflects the combined influences of changes in the equatorial
thermocline, the properties of the thermocline's source waters, atmospheric
greenhouse gas content, and orbital variations on sea surface temperature (SST)
and biological productivity over the past 5 million years. Our data indicate that
the intensification of Northern Hemisphere glaciation ~3 million years ago did not
interrupt an almost monotonic cooling of the EEP during the Plio-Pleistocene.
SST and productivity in the eastern tropical Pacific varied in phase with global
ice volume changes at a dominant 41,000-year (obliquity) frequency throughout
this time. Changes in the Southern Hemisphere most likely modulated most of the
changes observed.
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