- 1Aix-Marseille Université, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France
- 2Department of Climate Geochemistry, Max Planck Institute for Chemistry, Mainz, Germany
- 4Department of Geosciences, University of Tübingen, Tübingen, Germany
The Mediterranean Sea, a semi-enclosed basin, has experienced periodic anoxic events that resulted in sapropels—organic-rich sediment layers formed during deep-water oxygen depletion. While the main processes driving sapropel formation are understood, the ecological and morphological responses of planktonic species to these extreme conditions remain largely unexplored. This study aims to fill this gap by examining the composition, tolerance, and ecological responses of calcareous planktonic species, with a focus on planktonic foraminifera Globigerinoides ruber morphotypes and pteropod populations across sapropel formation events. To investigate these responses, we analyzed one sediment core retrieved from the Gulf of Sirte, covering the last 130 k years with a focus on sapropels S1 and S5. Microfossil samples were investigated using a microfossil sorter (MiSo) Robot at CEREGE, which automatically images and measures microfossils from the coarse sediment fraction, unlike conventional approaches, which focus on species abundance and identification solely. This approach allowed us to determine both abundance and size of the different specimens, at the species level, through the training of a Convolutional Neural Network (CNN) which was applied to label a large dataset (160,000 images). Our results reveal significant shifts in planktonic community composition and diversity throughout the sapropels S1 and S5. Planktonic foraminifera diversity decreased during sapropels, notably with a reduction in species like Globigerinoides ruber and Globigerinoides elongatus. In contrast, pteropod abundance increased, suggesting they may be more resilient to environmental changes due to their higher motility compared to foraminifera and lower species competition during these anoxic periods. Size variations in dominant species were also observed, with distinct changes linked to environmental stressors such as lower salinity. This study provides valuable insights into the resilience and adaptability of planktonic species environmental changes, offering a more refined understanding of sapropel-related ecological impacts on marine communities.
How to cite: Chaabane, S., de Garidel-Thoron, T., Schultz, H., Conrod, S., and Tachikawa, K.: Ecological responses of planktonic foraminifera and pteropods to sapropel formation in the eastern Mediterranean Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15986, https://doi.org/10.5194/egusphere-egu25-15986, 2025.