Equatorial Pacific climatic variations during the Miocene - Pliocene at IODP-Site U-1338
Abstract
The modern Equatorial Pacific setting has been established during the late Miocene-Pliocene. We provide here a new record of Equatorial Pacific sea surface conditions during the Miocene-Pliocene at IODP Site U1338 (2°30.469’N, 117°58.178’W), which contains a continuous and well-preserved sedimentary record. Our reconstruction is mainly based on stable isotopic measurements of oxygen and carbon on bulk carbonate, planktonic foraminifera and calcareous nannofossils 2-5 µm, as well as the alkenone unsaturation index (Uk’37) proxy. The data provide a new and detailed alkenone based SST reconstruction for mid-Miocene through Pliocene in the Eastern Equatorial Pacific and indicate a steady trend about 27 °C during mid-Miocene. Coccolith δ18O curve shows no resemblance to the benthic isotope curve established by Zachos et al. (2001) and shows an anti-correlation with alkenone based SST from 6.5 Ma, indicating that isotopic sea surface variations are mainly controlled by the temperature. Especially, these curves point jointly to a rapid cooling from 3.5 Ma. Moreover, sea surface temperatures variations fluctuate in parallel with cycles of environment fertility at about 2 Ma, supported by δ13C variations and modifications of nannofossil assemblages, and permit to hypothesize regular fluctuations of under current circulation. Combined these results with climatic and tectonic evolutions allow to demonstrate a series of paleoceanographic events, including: - High-productivity conditions characterized the mid-Miocene time interval. - The “carbonate crash”, around 11-9 Ma, during which deep oceanic conditions changes occurred, are assigned to the closing of the Panama gateway. - The late Miocene, in which the Indonesian and Central American seaways are gradually narrowing. The east-west Pacific circulations are then restricted and we hypothesize the gradual establishment of long-term El Niño-La Niña-like oceanic and climatic conditions, with the settlement of the Equatorial Under Current. - The late Pliocene global cooling is linked with the onset of the Northern hemisphere glaciation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMPP23A1729R
- Keywords:
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- 1041 GEOCHEMISTRY / Stable isotope geochemistry;
- 4231 OCEANOGRAPHY: GENERAL / Equatorial oceanography