Calcareous nannoplankton response to a high CO2 world: evidence from sediment traps (Aegean and Ionian Seas) and Pliocene paleofluxes

One of the most enigmatic features of long-term Cenozoic climatic evolution, with some analogue potential for present/ future global climate change, is the last sustained warm and high-atmospheric CO2 interval in Earth’s history. The Pliocene is the most recent period in Earth’s history when average global temperature, atmospheric CO2 concentrations, and sea level were higher than today. This time period offers an appropriate interval to understand the climatic processes of a warm, high CO2 world, similar to the ongoing climatic conditions. Also, due to the high absorption capacity of the Eastern Mediterranean to anthropogenic CO2, the study area (Aegean and Ionian seas) is an ideal location to assess the impact of anthropogenic ocean acidification on calcifying organisms. The main objective of the present study is to investigate calcareous nannoplankton fluxes in the NE Mediterranean Sea as recorded by sediment traps and paleoceanographic records. The study material is collected from sediment traps in the Aegean and Ionian Seas and from the sedimentary record of the Eastern Mediterranean Deep Sea Drilling Project (DSDP Leg42A, Site 378). In the present study, coccolith fluxes from sediment traps were examined and compared in different sites of the Aegean and Ionian Seas. Data were compared in order to define the spatial and seasonal variability in assemblage composition and coccolithophore fluxes. The present study reflects in the coccolithophore export productivity the context of biogenic sedimentation in the water column. Furthermore, a water and sediment trap samples (N.Aegean Sea) analysis was carried out and through the comparison with data derived from surface sediment of the same site, valuable information were provided on the alterations observed in coccolithophore assemblage composition during their export from the euphotic zone to the seafloor. In addition, the morphometric analysis of coccoliths contributed to the investigation of water masses in the water column of the North Aegean Sea. In the DSDP core data we focus on the “warm Pliocene” interval, after the Zanclean “flooding” phenomenon in the Aegean after the Messinian Mediterranean Salinity Crisis (Zanclean reflooding). According to the detailed biostratigraphy and the derived age model, this study presents a composite dataset of the two boreholes of DSDP-Leg42A-Site 378 for the interval 3.8-5.08Ma. Subsequently, we studied how coccolithophores adapted to the Pliocene environment by quantifying their abundance through paleofluxes, species composition and correlation with geochemical paleo-indices analyses performed on the core material. In addition, the DSDP sedimentary record provided evidence on the Zanclean reflooding mechanism in the Cretan Basin. This study aims to improve our understanding of long-term adaptation strategies of calcareous nannoplankton in warm, high-CO2 climates by combining present-day evidence with Lower Pliocene fossil time series.

Skampa, E. A., 2022. Calcareous nannoplankton response to a high CO2 world: evidence from sediment traps (Aegean and Ionian Seas) and Pliocene paleofluxes. PhD Thesis, National and Kapodistiran University of Athens. Thesis (restricted access).

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