HR: 0800h
AN: PP51B-0596    [Abstracts]
TI: Reconstruction of Sea Surface Temperatures During Cretaceous Oceanic Anoxic Events Using Archaeal Paleothermometry
AU: * Schouten, S
EM: schouten@nioz.nl
AF: Department of Marine Biogeochemistry & Toxicology, Royal Netherlands Institute for Sea Research, PO Box 59, Den Burg, 1788 AB Netherlands
AU: Forster, A
EM: forster@nioz.nl
AF: Department of Marine Biogeochemistry & Toxicology, Royal Netherlands Institute for Sea Research, PO Box 59, Den Burg, 1788 AB Netherlands
AU: Hopmans, E C
EM: hopmans@nioz.nl
AF: Department of Marine Biogeochemistry & Toxicology, Royal Netherlands Institute for Sea Research, PO Box 59, Den Burg, 1788 AB Netherlands
AU: Wagner, T
EM: Thomas.Wagner@newcastle.ac.uk
AF: School of Civil Engineering and Geosciences University of Newcastle, Dev0nshire Building 4.08, Newcastle upon Tyne, NE1 7RU United Kingdom
AU: Stusser, I
EM: i.stuesser@uni-koeln.de
AF: Institute for Geology and Mineralogy, University of Cologne, Zlpicher Str. 49a, Cologne, 50674 Germany
AU: Dumitrescu, M
EM: mdumitre@indiana.edu
AF: Biogeochemical Laboratories, Department of Geological Sciences, Indiana University at Bloomington, Bloomington, IN 47405-1403 United States
AU: Brassell, S C
EM: simon@indiana.edu
AF: Biogeochemical Laboratories, Department of Geological Sciences, Indiana University at Bloomington, Bloomington, IN 47405-1403 United States
AU: Sininghe Damste, J S
EM: damste@nioz.nl
AF: Department of Marine Biogeochemistry & Toxicology, Royal Netherlands Institute for Sea Research, PO Box 59, Den Burg, 1788 AB Netherlands
AB: During past "oceanic anoxic events" (OAEs) large parts of the ancient oceans were stratified likely due to the plate tectonic continent configuration. These OAEs are also characterized by large shifts in ¹³C in carbonate and carbon. In a number of OAEs organic carbon and carbonate became substantially enriched in ¹³C likely due to enhanced organic matter burial rates in sediments and, thus, removal of ¹³C-depleted organic matter from the ocean and atmosphere. However, in some instances such as the Aptian OAE 1a, carbonate and organic carbon also exhibit negative carbon isotope excursions which have been attributed to the massive release of ¹³C-depleted methane from gas hydrates. Regardless of the direction of the isotope shift they all indicate significant perturbations of the global carbon cycle and often substantial shifts in the atmospheric composition of greenhouse gases such as CO₂. The consequences of these perturbations must be substantial especially on sea surface temperatures (SST). For quantification of Cretaceous SST we presently rely on δ¹³O palaeothermometry of carbonate tests (in particular foraminifera). However, during OAEs carbonate and foraminifera are poorly preserved or severely affected by dissolution and preclude a complete and accurate SST reconstruction. Alkenones paleothermometry may provide an alternative method for SST determination but, unfortunately, alkenones are sparse in sediments of this age and they are limited to temperatures <29%°C which may be frequently exceeded in this time period. We recently have developed a new organic temperature proxy, the TEX86, based on lipids present in the membranes of marine crenarchaeota. A study of marine surface sediments from all over the globe showed that these organisms adjust the composition of their tetraether membranes lipids as a response to SST. This response, quantified as the TEX₈₆, is well described by a linear relationship (r² = 0.95) and can thus be used to determine SST from the tetraether membrane composition preserved in sediments. For the present study a number of black shales from different Cretaceous time periods and deposited during OAEs were analysed for the TEX₈₆ proxy. In addition, stable carbon isotopic records of carbonate, organic carbon and, in some cases, specific molecules were also obtained. Black shales deposited during the OAE1a in the tropical Pacific at Shatsky Rise, the OAE1b in the tropical Tethys at the Mazagan Platau, and the OAE2 in the tropical Tethys at Demerara Rise were analysed. All records revealed substantially higher temperatures than present-day tropical oceans but with substantial warming and cooling periods. The stable carbon isotope records show various abrupt positive and negative spikes revealing that during all these OAEs the global carbon cycle was substantially affected. The changes in stable carbon isotopes were often synchronous with changes in SST suggesting that the perturbations of the carbon cycle had major consequences for global climate.
DE: 0424 Biosignatures and proxies
DE: 0428 Carbon cycling (4806)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1055 Organic and biogenic geochemistry
DE: 4954 Sea surface temperature
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005