HR: 08:30h
AN: PP41D-03    [Abstracts]
TI: A Multiple Proxy and Modeling Study of Cretaceous Upper Ocean Temperatures and Atmospheric Carbon Dioxide Concentrations From Tropical Atlantic Sediments
AU: * Bice, K L
EM: kbice@whoi.edu
AF: Dept. Of Geology & Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Birgel, D
EM: dbirgel@uni-bremen.de
AF: Research Center Ocean Margins, University of Bremen, Bremen, D-28334 Germany
AU: Meyers, P A
EM: pameyers@umich.edu
AF: Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109 United States
AU: Dahl, K A
EM: kdahl@whoi.edu
AF: Dept. Of Geology & Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Hinrichs, K
EM: khinrichs@uni-bremen.edu
AF: Research Center Ocean Margins, University of Bremen, Bremen, D-28334 Germany
AU: Norris, R D
EM: rnorris@ucsd.edu
AF: Scripps Institution of Oceanography, 308 Vaughan Hall, La Jolla, CA 92093 United States
AB: Tropical Atlantic upper ocean temperatures have been reconstructed using oxygen isotope and Mg/Ca ratios in well-preserved planktonic foraminifera extracted from Albian through Santonian black shales recovered during Ocean Drilling Program Leg 207 (North Atlantic Demerara Rise). Based on a range of plausible assumptions regarding seawater composition at the time, the data support temperatures between 33 and 42 degrees Celsius. In a low resolution dataset spanning 84-100 Ma, a local temperature maximum occurs in the late Turonian and a possible minimum occurs in the mid- to early late Cenomanian. The relation between single species foraminiferal oxygen isotope ratios and Mg/Ca suggests that the ratio of magnesium to calcium in the Turonian-Coniacian ocean may have been lower than in the Albian-Cenomanian ocean, perhaps coincident with an ocean strontium isotope minimum. The carbon isotopic compositions of distinct marine algal biomarkers were measured in the same sediment samples. The values of phytane carbon isotope ratios, foraminiferal carbon isotope ratios and inferred temperatures were used to estimate atmospheric carbon dioxide concentrations through this interval. Estimates of atmospheric carbon dioxide concentrations range between 600 and 2400 ppmv. Within the uncertainty in the various proxies, there is only a weak overall correspondence between higher (lower) tropical temperatures and more (less) atmospheric carbon dioxide. The GENESIS climate model under-predicts tropical Atlantic temperatures inferred from ODP Leg 207 foraminiferal oxygen isotope and Mg/Ca ratios when we specify approximate carbon dioxide concentrations estimated from the biomarker isotopes in the same samples. Possible errors in the temperature and carbon dioxide estimates and possible deficiencies in the model will be discussed. The potential for, and effects of, substantially higher atmospheric methane during Cretaceous anoxic events will be examined.
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4930 Greenhouse gases
DE: 4954 Sea surface temperature
DE: 9610 Cretaceous
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005