DIACHRONOUS RECOVERY OF DIFFERENT PLANKTON GROUPS FOLLOWING THE END-CRETACEOUS MASS EXTINCTION

Our understanding of how planktic ecosystems will respond to anthropogenic warming is limited. Using a holistic approach to measure ecosystems within the geological record we can better understand ecosystem responses to climate perturbations. Utilizing sediment recovered from the El Kef Coring Project, near the Cretaceous-Paleogene (K/Pg) Global Stratotype Section and Point at El Kef (Tunisia), we present a combined record of planktic foraminifera, calcareous nannofossils and organic biomarkers from the latest Maastrichtian Plumerita hantkeninoides Zone to the early Danian Zone P2. We measure diversity in planktic foraminifera and nannofossils using effective (Hill) numbers, where diversity is measured along a gradient of q where integers correspond to common diversity metrics. We then compare diversity in fossilizing plankton to organic biomarker records.

Using this approach, we show that non-fossilizing and fossilizing plankton recover at different rates through the Danian with fluctuating dominance within each group. Planktic foraminifera species richness declined rapidly during the K/Pg extinction and did not recover to pre-extinction levels within the study interval (indeed, richness did not increase after Pα). In contrast, nannofossil richness doubles from P0 to P1c then remains constant through to the end our record. When abundance is considered nannofossils and planktic foraminifera show differing diversity dynamics. Planktic foraminifera diversity appears to be controlled two opportunistic genera Guembelitria and Chiloguembelina causing large diversity fluctuations in the first 300Kyr of extinction recovery. Calcareous nannofossil assemblages in contrast show subdued diversity changes with low diversity through the first 300Kyr gradually increasing through P1c into P2 where diversity peaks. Similarly, to the planktic foraminifera, calcareous nannofossil diversity seems to be controlled by competition, with diversity only increasing when the disaster taxa Neobiscutum spp. disappears. While initial analysis indicates that planktic foraminifera show limited correlation with organic biomarker changes, the timing of increased calcareous nannofossil diversity coincides with a decrease in dinoflagellates. These relationships need to be investigated further.