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Title:
The Cretaceous Thermal Maximum and Oceanic Anoxic Event 2 in the Tropics: Sea- Surface Temperature and Stable Organic Carbon Isotopic Records from the Equatorial Atlantic
Authors:
Forster, A.; Schouten, S.; Baas, M.; Moriya, K.; Wilson, P. A.; Sinninghe Damsté, J. S.
Affiliation:
AA(Royal Netherlands Institute for Sea Research, Department of Marine Biogeochemistry and Toxicology P.O. Box 59, Den Burg, 1790 AB Netherlands ), AB(Royal Netherlands Institute for Sea Research, Department of Marine Biogeochemistry and Toxicology P.O. Box 59, Den Burg, 1790 AB Netherlands ;), AC(Royal Netherlands Institute for Sea Research, Department of Marine Biogeochemistry and Toxicology P.O. Box 59, Den Burg, 1790 AB Netherlands ;), AD(National Oceanography Centre Southampton, School of Ocean and Earth Science University of Southampton European Way, Southampton, SO14 3ZH United Kingdom ;), AE(National Oceanography Centre Southampton, School of Ocean and Earth Science University of Southampton European Way, Southampton, SO14 3ZH United Kingdom ;), AF(Royal Netherlands Institute for Sea Research, Department of Marine Biogeochemistry and Toxicology P.O. Box 59, Den Burg, 1790 AB Netherlands ;)
Publication:
American Geophysical Union, Fall Meeting 2006, abstract #PP33C-04
Publication Date:
12/2006
Origin:
AGU
Keywords:
1041 Stable isotope geochemistry (0454, 4870), 4900 PALEOCEANOGRAPHY (0473, 3344), 4901 Abrupt/rapid climate change (1605), 4954 Sea surface temperature, 9610 Cretaceous
Bibliographic Code:
2006AGUFMPP33C..04F

Abstract

Oceanic Anoxic Event 2 (OAE-2) occurring during the Cenomanian/Turonian transition, is evident from a global positive stable carbon isotopic excursion and presumably represents the most extreme carbon cycle perturbation of the last 100 Myr. However, the impact of this major perturbation on and interaction with global climate remains unclear. OAE-2 occurred in the mid-Cretaceous, a time in Earth history characterized by extreme global warmth culminating in the so-called Cretaceous thermal maximum. Thus, records of paleo-sea surface temperatures (SSTs) from the mid-Cretaceous oceans are particularly important for understanding greenhouse climate conditions. We will present new high-resolution SST-records based on an organic proxy, the TetraEther indeX of 86 carbon atoms (TEX86), and δ18O of excellently preserved, "glassy" planktic foraminifera, combined with stable organic carbon isotopes generated from marine black shales located offshore Suriname/French Guiana (ODP Site 1260) and Senegal (DSDP Site 367). At Site 1260 a good match between conservative SST estimates from TEX86 and δ18O is observed. Late Cenomanian SSTs in the equatorial Atlantic Ocean (~33°C) were substantially warmer than today (~27-29°C) and the onset of OAE-2 coincided with a rapid shift to an even warmer (~35-36°C) regime. Within the early stages of OAE-2 a marked (~4°C) cooling is observed. However, well before the termination of OAE-2, the warm regime was re-established and persisted into the Turonian. Our findings corroborate the view that the C/T-transition represents the onset of peak Cretaceous warmth, that mid-Cretaceous warmth can be attributed to high levels of atmospheric CO2 and that major OAEs were capable of triggering global cooling through the negative feedback effect of organic carbon burial-led CO2-sequestration. However, the factors that gave rise to the observed shift to a warmer climate regime at the onset of OAE-2 were sufficiently powerful that they were only briefly counterbalanced by high rates of carbon-burial attained during OAE-2. The latter becomes even more evident when our detailed dual-proxy SST-records from ODP Site 1260 are compared to the long-term evolution of mid-Cretaceous tropical SSTs at Demerara Rise. Here, we monitored the Albian to Santonian SST-history of the western equatorial Atlantic by generating a solely TEX86 based combined record that spans the entire Cretaceous black shale sequence at ODP Sites 1258 and 1259 in meter-scale resolution, which was recently completed and will be presented here for the first time. Once established the extreme warm climate regime (characterized by averaged tropical SSTs exceeding 35°C) lasted well into the Coniacian at Demerara Rise. However, during the Turonian, several pronounced but relatively short-lived cooler intervals punctuate this otherwise remarkably stable interval of extreme tropical warmth. This observation shows that rapid tropical SST-changes occurred also during the Cretaceous thermal maximum, and implies that even the mid-Cretaceous "super-greenhouse" climate may have been less stable than previously thought.
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