Response of calcareous nannofossils to the Paleocene-Eocene thermal maximum from a shelf section in Jordan

Abstract

Abstract The Paleocene-Eocene Thermal Maximum (PETM) is known as an approximately 200 kyr long lasting interval of extreme global warming accompanied by major alterations in the ocean-atmosphere system. These include a negative carbon isotope excursion, intense carbonate dissolution and biotic changes of marine floras and faunas. The current study reports the response of calcareous nannofossils across the Paleocene-Eocene boundary in a paleoshelf setting in Jordan (core OS-28), clearly marked by a negative δ 13 C org excursion and the occurrence of characteristic “excursion taxa” (e.g., Discoaster araneus , Rhomboaster spp., Coccolithus bownii ). While this section suffers from intense dissolution at the onset of the event and the peak of the isotopic excursion, it retains well-preserved, diverse nannofossil assemblages from the pre-PETM, PETM recovery and post-PETM intervals. These assemblages are dominated by two taxa of inferred mesotrophic affinities ( Coccolithus pelagicus , Toweius spp.) and show only low abundances of oligotrophic taxa ( Discoaster spp., Fasciculithus spp., Sphenolithus spp.). Overall, there appear to be only relatively low-level changes in the general assemblage composition across the PETM. During the post-PETM, however, there was a gradual decrease in relative abundance of C. pelagicus and Toweius spp. This decline co-coccured with a relative increase of Coccolithus bownii and Coccolithus foraminis , and in its later phase was accompanied by an increase in the relative abundance of Sphenolithus spp. These changes, indicate a possible shift towards less fertile conditions following the hyperthermal event. The relatively muted signal of biotic change associated with the PETM interval at this site was partly a consequence of poor preservation within the key sequence of the studied core. On the other hand, the low signal may also be indicative for local environment processes, such as variations in riverine sourced nutrients, salinity, turbidity. Operating on a regional scale, these local factors overrode the direct and indirect temperature signals that are the dominant control on nannofossil communities across the PETM in open ocean sites. Finally, the assemblages from the Jordan section highlight further the overall spatial heterogeneity in reported responses of shelf area communities to the PETM interval. These heterogeneities have been observed in shelf assemblages from Tanzania, New Jersey and the Tethyan margins, which again points to the strong influence of regional controls like river input in more marginal settings.