Tropical Atlantic climate and ecosystem regime shifts during the Paleocene–Eocene Thermal Maximum
- 1Marine Palynology and Paleoceanography, Laboratory of Palaeobotany and Palynology, Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Heidelberglaan 2, 3584CS Utrecht, the Netherlands
- 2Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Princetonplein 9, 3584CC Utrecht, the Netherlands
- 3NIOZ Royal Netherlands Institute for Sea Research, 1790AB Den Burg, Texel, the Netherlands
- 4MARUM – Center for Marine Environmental Sciences, University of Bremen, Leobener Straße 8, 28359, Bremen, Germany
- 5Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Waterfront Campus European Way Southampton, SO14 3ZH, UK
Abstract. The Paleocene–Eocene Thermal Maximum (PETM, 56 Ma) was a phase of rapid global warming associated with massive carbon input into the ocean–atmosphere system from a 13C-depleted reservoir. Many midlatitude and high-latitude sections have been studied and document changes in salinity, hydrology and sedimentation, deoxygenation, biotic overturning, and migrations, but detailed records from tropical regions are lacking. Here, we study the PETM at Ocean Drilling Program (ODP) Site 959 in the equatorial Atlantic using a range of organic and inorganic proxies and couple these with dinoflagellate cyst (dinocyst) assemblage analysis. The PETM at Site 959 was previously found to be marked by a ∼ 3.8 ‰ negative carbon isotope excursion (CIE) and a ∼ 4 °C surface ocean warming from the uppermost Paleocene to peak PETM, of which ∼ 1 °C occurs before the onset of the CIE. We record upper Paleocene dinocyst assemblages that are similar to PETM assemblages as found in extratropical regions, confirming poleward migrations of ecosystems during the PETM. The early stages of the PETM are marked by a typical acme of the tropical genus Apectodinium, which reaches abundances of up to 95 %. Subsequently, dinocyst abundances diminish greatly, as do carbonate and pyritized silicate microfossils. The combined paleoenvironmental information from Site 959 and a close-by shelf site in Nigeria implies the general absence of eukaryotic surface-dwelling microplankton during peak PETM warmth in the eastern equatorial Atlantic, most likely caused by heat stress. We hypothesize, based on a literature survey, that heat stress might have reduced calcification in more tropical regions, potentially contributing to reduced deep sea carbonate accumulation rates, and, by buffering acidification, also to biological carbonate compensation of the injected carbon during the PETM. Crucially, abundant organic benthic foraminiferal linings imply sustained export production, likely driven by prokaryotes. In sharp contrast, the recovery of the CIE yields rapid (≪ 10 kyr) fluctuations in the abundance of several dinocyst groups, suggesting extreme ecosystem and environmental variability.