Paleo-environmental Reconstructions of the Paleocene Equatorial Atlantic Ocean based upon Biomarkers and Dinoflagellate Cysts

Abstract

In contrast to the warm early-Eocene “hothouse” conditions (~56-51 Ma), which was subject to comparable CO2 concentrations as predicted for our future assuming unabated anthropogenic fossil fuel consumption (Archer, 2005), the “greenhouse” mid-Paleocene (~62-58 Ma) has been barely investigated. The latter despite the potential similarities with the present-day climate system in terms of atmospheric pCO2. Uncertainty about the presence of substantial polar ice-sheets during the mid-Paleocene episode and the warming which led to this “hothouse”, particularly for the data-lacking tropics, remains significant. To gain new insights in this matter, this study presents reconstructions of the marine paleo-environment, paleo-temperatures, and sea-level fluctuations. These reconstructions were done by investigating palynomorph assemblages (notably organic-walled dinoflagellate cysts) and applying paleo-thermometers TEX86 and MBT/CBT on equatorial Paleocene sediments from ODP site 959D, offshore Ivory Coast (west-Africa). Unfortunately, the biomarker analyses did not result in any quantitative reconstructions for land and sea surface temperature as the sediments were too mature. Dinocyst events however allowed the existing stratigraphic age model to be considerably improved for the Paleocene part of the model. Furthermore the combined results from the applied palynological proxies and results of related studies, for instance d18O isotope trends as detailed by Westerhold et al. (2011), reflect that the most plausible pronounced continental ice-sheet presences are suspected for the mid-to-late Paleocene, although supporting evidence is thin. These combined results also imply a prevailing open marine to pelagic setting at Paleocene site 959, where paleo-productivity was predominantly controlled by wind-induced upwelling, riverine input, stratification and sea-level shifts.