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Early Maastrichtian carbon cycle perturbation and cooling event: implications from the South Atlantic Ocean

By Oliver Friedrich, Jens O. Herrle, Paul A. Wilson, Matthew J. Cooper, Jochen Erbacher and Christoph Hemleben


Published stable isotope records in marine carbonate are characterized by a positive ?18O excursion associated with a negative ?13C shift during the early Maastrichtian. However, the cause and even the precise timing of these excursions remain uncertain. We have generated high-resolution foraminiferal stable isotope and grey scale records for the latest Campanian to early Maastrichtian (~73-68 Ma) at two Ocean Drilling Program sites, 525 (Walvis Ridge) and 690 (Weddell Sea). We demonstrate that the negative ?13C excursion is decoupled from the ?18O increase with a lag of about 600 kyr. Our ?13C records (both planktic and benthic) show an amplitude for the negative excursion of 0.7 ‰ that falls between about 72.1 and 70.7 Ma. Our planktic ?18O records indicate an overall increase of 1.2 ‰ from 73 to 68 Ma at Site 690, whereas at Site 525 they record a slightly smaller increase (~1 ‰) that peaks around 70.1 Ma with decreasing values thereafter. Our benthic ?18O data indicate an increase of ~1.5 ‰ at Site 525 and ~0.7 ‰ at Site 690 between about 71.4 and 69.9 Ma. Benthic ?18O values show different baseline values at the two sites before and after the excursion but the larger increase at Site 525 means that the values attained at the peak of the excursion are similar at the two sites. We interpret this observation in terms of water mass changes. The excursion is interpreted to reflect a cooling of bottom waters in response to the strengthening contribution of intermediate- to deep-water production in the high southern latitudes rather than increased ice volume. The associated carbon-cycle perturbations that we observe are interpreted to reflect a weakening of surface-water stratification and increased productivity, as supported by our grey value data

Topics: QE, GC
Year: 2009
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Provided by: e-Prints Soton
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