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High-latitude influence on the eastern equatorial Pacific climate in the early Pleistocene epoch


Many records of tropical sea surface temperature and marine productivity exhibit cycles of 23 kyr (orbital precession) and 100 kyr during the past 0.5 Myr (refs 1–5), whereas high-latitude sea surface temperature records display much more pronounced obliquity cycles at a period of about 41 kyr (ref. 6). Little is known, however, about tropical climate variability before the mid-Pleistocene transition about 900 kyr ago, which marks the change from a climate dominated by 41-kyr cycles7 (when ice-age cycles and high-latitude sea surface temperature variations were dictated by changes in the Earth's obliquity8,9) to the more recent 100-kyr cycles of ice ages. Here we analyse alkenones from marine sediments in the eastern equatorial Pacific Ocean to reconstruct sea surface temperatures and marine productivity over the past 1.8 Myr. We find that both records are dominated by the 41-kyr obliquity cycles between 1.8 and 1.2 Myr ago, with a relatively small contribution from orbital precession, and that early Pleistocene sea surface temperatures varied in the opposite sense to local annual insolation in the eastern equatorial Pacific Ocean. We conclude that during the early Pleistocene epoch, climate variability at our study site must have been determined by high-latitude processes that were driven by orbital obliquity forcing.

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Figure 1: Time series of alkenone abundances (C37 total), SST, ice volume19 (benthic δ18O) and local annual insolation at ODP Site 846.
Figure 2: Evolution of spectral densities in the entire Pleistocene (0–1.8 Myr ago).
Figure 3: Coherencies and phase relationships in the early Pleistocene (1.2–1.8 Myr ago).


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We thank the curators of the Ocean Drilling Program (Texas A&M University) for providing samples. The original draft was improved by comments from S. Clemens, K. Lawrence and L. Lisiecki. This work was supported by the NSF (T.D.H.).

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Correspondence to Zhonghui Liu.

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Supplementary information

Supplementary Figure 1

Location of ODP Site 846 in the eastern Pacific Ocean. (PDF 211 kb)

Supplementary Figure 2

Normalized Pleistocene SST and (log-transformed) alkenone abundance records, with filtered obliquity and precession signals. (PDF 542 kb)

Supplementary Figure 3

Coherencies and phase relationships in the late Pleistocene (0-0.6 Ma). (PDF 272 kb)

Supplementary Figure Legends (DOC 20 kb)

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Liu, Z., Herbert, T. High-latitude influence on the eastern equatorial Pacific climate in the early Pleistocene epoch. Nature 427, 720–723 (2004).

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