Calcareous nannoplankton paleofluxes in the early Pliocene sapropels of the South Aegean Sea, NE Mediterranean: biogenic carbonate contribution and paleoecological implications

Calcareous nannoplankton, one of the major contributors to marine primary production, not only responds quickly to variations in environmental conditions, but provides excellent means of first-order biostratigraphy. In our study we use early Pliocene sediments from the Cretan Sea (South Aegean; DSDP- Leg 42A, Site 378). The location of the record allows us to investigate formation processes of the Zanclean sapropelic layers in South Aegean Sea, and unravel the effects of monsoonal activity, as well as characterize any high latitude teleconnections of the area, prior to the mid-Pliocene warm period. The obtained nannofossil biostratigraphy provided the first-order bed-to-bed age control during the time interval of 5.08-3.98 Myrs, enabling the astronomical tuning of the marly–sapropelic cycles 12-59 to the target-curves.

Geochemical analysis  (total organic carbon, oxygen, nitrogen, organic and carbonate carbon stable isotopes) were performed, revealing variations in carbon cycle and paleoceanographic conditions, as also variability in the redox conditions of the basin. Planktonic foraminifera δ¹⁸O and δ¹³C records are comparable to the global and Mediterranean Sea stacks, revealing warmer conditions in between approx. 5.08-4.9, in accordance to high summer insolation variation values. The quantification of the early Pliocene nannoplankton paleofluxes, indicated approximately two times higher average accumulation rates for the past export production during the sapropelic layers in respect to the non-sapropelic intervals; suggesting that primary productivity was a major component of the sapropelic formation procedures. Overall, calcareous nannofossil assemblage was dominated by Reticulofenestra spp. <5μm (up to 74%) followed by Florisphaera profunda (up to 64%). Other major species of the assemblage composition were Umbilicosphaera spp., Calcidiscus spp. and Helicosphaera spp. F. profunda showed an increase in paleofluxes within the sapropelic layers, coupled with relatively decreased accumulation rates of the upper photic zone taxa and high stratification index, thus suggesting an ecological depth-separation of the water column and a nutrient-rich lower photic zone.

 

Acknowledgments
We acknowledge support of this work by the Action ‘National Network on Climate Change and its Impacts – CLIMPACT’, funded by the Public Investment Program of Greece (GSRT, Ministry of Development and Investments). E. Skampa has been granted with a scholarship from the State Scholarships Foundation. This research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme « Human Resources Development, Education and Lifelong Learning» in the context of the project “Strengthening Human Resources Research Potential via Doctorate Research” (MIS-5000432), implemented by the State Scholarships Foundation (ІΚΥ).