Planktic foraminifera assemblage composition and flux dynamics inferred from an annual sediment trap record in the Central Mediterranean Sea

Abstract

Abstract. The Sicily Strait, located in the central Mediterranean Sea, represents a key point for the regional oceanographic circulation as it is considered the sill that separates the western and eastern basins. Therefore, it is considered a unique zone regarding the well-documented west-to-east Mediterranean productivity gradient. Here we document the planktic foraminifera assemblages retrieved by the C01 sediment trap between November 2013 and October 2014. 19 samples from the sediment trap deployed at a water depth of around 400 m have been used. More than 3700 individuals and 15 different species have been identified. Globorotalia inflata, Globorotalia truncatulinoides, Globigerina bulloides, Globigerinoides ruber and ruber (pink) were the five main species identified, accounting for more than 85 % of the total foraminifera. The total planktic foraminifera flux mean value was 630 shells m-2 d-1, with a minimum value of 45 shells m-2 d-1displayed during late autumn 2013 and a maximum of 1890 shells m-2 d-1 reached during spring 2014. Most of the species fluxes followed a similar pattern. This is likely the result of the regional oceanographic configuration and the marked seasonality in the surface circulation. During spring and winter, the Atlantic waters dominate the surface circulation, bringing cool and nutrient enriched waters. This results in a planktic foraminifera flux increase and a dominance of western basin taxa. During summer and autumn, the circulation is dominated by the eastern warm and oligotrophic Levantine water, which results in planktic foraminifera flux decrease and the dominance of easter basin species. Our comparison with satellite derived SST and chlorophyll-a data showed that G. inflata was associated with cool and nutrient rich conditions, while both G. ruber morphotypes were associated with warm and oligotrophic conditions. However, no trends were identified for G. truncatulinoides or G. bulloides. In addition, a comparison of the Sicily Strait data with other Mediterranean time series located in the Alboran Sea, Gulf of Lions and the Levantine basin was carried out. Our data indicated that the annualized planktic foraminifera flux was lower than in the westernmost Alboran Sea but higher than in the easternmost Levantine basin. However, the Sicily Strait species diversity was the highest among the compared zones, highlighting the influence of the different basins and its transitional aspect from a planktic foraminifera population perspective. Finally, we compared the sediment trap planktic foraminifera assemblage with the assemblages from seabed sediment located in the vicinity of the Sicily Strait. Our results showed that the sediment trap population significantly differed from the assemblages in the seabed sediment. The deep-dwelling species dominated the sediment trap samples, while eutrophic and oligotrophic species were significantly more abundant in the core-tops, highlighting a potential effect of the recent Mediterranean environmental change, such as warming and a potential shift in the oceanographical conditions on the planktic foraminifera population.