HR: 0800h
AN: PP51B-0597    [Abstracts]
TI: Perturbation of Aptian and Valanginian Carbon Cycle and Marine Biocalcification Crises
AU: * Weissert, H
EM: weissert@erdw.ethz.ch
AF: Department of Earth Sciences, ETH-Z, Zuerich, 8092 Switzerland
AU: Burla, S
EM: Burla@erdw.ethz.ch
AF: Department of Earth Sciences, ETH-Z, Zuerich, 8092 Switzerland
AB: The mid-Cretaceous is known as a time of major perturbations of the global carbon cycle, which coincided with widespread biocalcification crises. Detailed Ccarbonate and Corganic carbon isotope records through the early Aptian show a prominent negative spike followed by a positive carbon isotope anomaly with amplitude of up to 3permil. Based on cyclostratigraphy, the negative C-isotope anomaly lasted up to a few hundred thousand years while the positive excursion had duration of up to millions of years. The negative spike coincides with low oxygen isotope values documented from the Pacific and Tethys Oceans. Tethyan carbon isotope data indicate that fractionation between marine organic matter and carbonate was largest during the time of most negative carbon isotope values. These data provide evidence that atmospheric carbon dioxide levels were highest during the time of the negative spike. The negative carbon isotope spike coincides with a major biocalcification crisis which is recorded in pelagic, neritic and coastal environments. New carbon and strontium isotope data from Aptian coastal successions in Portugal confirm that the most severe Aptian biocalcification crisis started before but culminated during negative carbon isotope anomaly. The widespread Aptian biocalcifcation crisis seems to have been triggered by elevated atmospheric CO2 values related to volcanic activity. Sudden methane release contributed to an amplification of greenhouse climate and it led to further weakening of marine calcification. Comparable calcification crises are recognized in the Valanginian. There, a negative carbon isotope anomaly recoding a methane pulse is not observed. Volcanic degassing alone seems to have triggered this calcification crisis. The positive carbon isotope excursions in the early Aptian and in the Valanginian following the biocalcification crises record the response of oceans and biota to greenhouse climate. Increased organic carbon burial and an accelerated fixation of carbon dioxide contributed to lower atmospheric carbon dioxide levels, to a cooling of climate and to marine conditions, which were again favorable for biocalcifying organisms.
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005