Sediment reworking rates in deep sediments of the Mediterranean Sea

Different pelagic areas of the Mediterranean Sea have been investigated in order to quantify physical and biological mixing processes in deep sea sediments. Herein, results of eleven sediment cores sampled at different deep areas (>2000 m) of the Western and Eastern Mediterranean Sea are presented. Pb-210(xs), and Cs-137 vertical profiles, together with C-14 dating, are used to identify the main processes characterising the different areas and, finally, controlling mixing depths (SML) and bioturbation coefficients (D-b). Radionuclide vertical profiles and inventories indicate that bioturbation processes are the dominant processes responsible for sediment reworking in deep sea environments. Results show significant differences in sediment mixing depths and bioturbation coefficients among areas of the Mediterranean Sea characterised by different trophic regimes. In particular, in the Oran Rise area, where the Almeria-Oran Front induces frequent phytoplankton blooms, we calculate the highest values of sediment mixing layers (13 cm) and bioturbation coefficients (0.187 cm(2) yr(-1)), and the highest values of Pb-210(xs) and Cs-137 inventories. Intermediate values of SML and D-b (similar to 6 cm and similar to 0.040 cm(2) yr(-1), respectively) characterise the mesothrophic Algero-Balearic basin, while in the Southern Tyrrhenian Sea mixing parameters (SML of 3 cm and D-b of 0.011 cm(2) yr(-1)) are similar to those calculated for the oligotrophic Eastern Mediterranean (SML of 2 cm and D-b of similar to 0.005 cm(2) yr(-1)).