• journal_title：Geology
• Contributor：Stefan Schouten ; Ellen C. Hopmans ; Astrid Forster ; Yvonne van Breugel ; Marcel M.M. Kuypers ; Jaap S. Sinninghe Damsté
• Publisher：Geological Society of America
• Date：2003-
• Format：text/html
• Language：en
• Identifier：10.1130/G19876.1
• journal_abbrev：Geology
• issn：0091-7613
• volume：31
• issue：12
• firstpage：1069

The middle Cretaceous (125–88 Ma) greenhouse world was characterized by high atmospheric CO₂ levels, the general absence of polar ice caps, and much higher global temperatures than at present. Both δ¹⁸O-based and model-based temperature reconstructions indicate extremely high sea-surface temperatures (SSTs) at high latitudes. However, there are a number of uncertainties with SST reconstructions based on δ¹⁸O isotope data of foraminifera due to diagenetic overprinting effects and tenuous assumptions with respect to the δ¹⁸O value of Cretaceous seawater, the paleoecology of middle Cretaceous marine organisms and seawater pH. Here we applied a novel SST proxy (i.e., TEX₈₆ [tetraether index of 86 carbon atoms], based on the membrane lipids of marine crenarchaeota) derived from middle Cretaceous sedimentary rocks deposited at low latitudes. The TEX₈₆ proxy indicates that tropical SSTs in the proto–North Atlantic were at 32–36 °C during the early Albian and late Cenomanian–early Turonian. This finding agrees with SST estimates based on δ¹⁸O paleothermometry of well-preserved foraminifera as well as global circulation model calculations. The TEX₈₆ proxy indicates cooler SSTs (27–32 °C) for the equatorial Pacific during the early Aptian, which is in agreement with SST estimates based on δ¹⁸O paleothermometry.