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Descent towards the Icehouse: Eocene sea surface cooling inferred from GDGT distributions

Research output: Contribution to journalArticle

Original languageEnglish
Pages (from-to)1000–1020
Number of pages21
JournalPaleoceanography
Volume30
Issue number7
Early online date27 Jun 2015
DOIs
DateAccepted/In press - 17 Jun 2015
DateE-pub ahead of print - 27 Jun 2015
DatePublished (current) - Jul 2015

Abstract

The TEX86 proxy, based on the distribution of marine isoprenoidal glycerol dialkyl glycerol tetraether lipids (GDGTs), is increasingly used to reconstruct sea surface temperature (SST) during the Eocene epoch (56.0-33.9 Ma). Here we compile published TEX86 records, critically re-evaluate them in light of new understandings in TEX86 palaeothermometry and supplement them with new data in order to evaluate long term temperature trends in the Eocene. We investigate the effect of archaea other than marine Thaumarchaeota upon TEX86 values using the branched-to-isoprenoid tetraether index (BIT), the abundance of GDGT-0 relative to crenarchaeol (%GDGT-0) and the Methane Index (MI). We also introduce a new ratio, %GDGTRS, which may help identify Red Sea-type GDGT distributions in the geological record. Using the offset between TEX86H and TEX86L (ΔH-L) and the ratio between GDGT-2 and GDGT-3 ([2]/[3]), we evaluate different TEX86 calibrations and present the first integrated SST compilation for the Eocene (55 to 34 Ma). Although the available data are still sparse some geographic trends can now be resolved. In the high-latitudes (>55 °), there was substantial cooling during the Eocene (~6 °C). Our compiled record also indicates tropical cooling of ~2.5°C during the same interval. Using an ensemble of climate model simulations that span the Eocene, our results indicate that only a small percentage (~10%) of the reconstructed temperature change can be ascribed to ocean gateway reorganisation or paleogeographic change. Collectively, this indicates that atmospheric carbon dioxide (pCO2) was the likely driver of surface water cooling during the descent towards the icehouse.

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Date of Acceptance: 17/06/2015

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    Rights statement: This is the final published version of the article (version of record). It first appeared online via Wiley at http://onlinelibrary.wiley.com/doi/10.1002/2014PA002723/abstract. Please refer to any applicable terms of use of the publisher.

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