Messinian salt fluxes into the present-day Eastern Mediterranean: implications for budget calculations and stagnation

Abstract

Although Messinian evaporites underly almost the entire Mediterranean, fluxes related to these evaporites have not been included in water- and salt budget calculations. Recently, long piston cores, recovered in the Eastern Mediterranean, were sampled for pore waters in sufficient detail to allow a semi-quantitative study of the sedimentary fluxes. Six different salt sources can be distinguished, namely those coming from: (1) normal pore waters, (2) mud diapirs, (3) sediments of formerly brine filled basins, (4) brine filled basins, (5) sediments from areas with a cobblestone topography, and (6) salt dissolution holes. Based on the chloride versus depth profiles, chloride fluxes from the sediment to the seafloor can be calculated. The fluxes were multiplied by the estimated areas for the different salt sources to obtain the total flux. These calculations show that mud diapirs and normal pore waters are the most important presently known salt sources in the Eastern Mediterranean. Compared with the “salt input” by evaporation, the sedimentary salt input is rather small and has little influence on the models used for the water- and salt budgets. Salt input from the sediment has a similar effect on the circulation of the Eastern Mediterranean water column as the introduction of huge amounts of fresh water at the surface. The latter process may have resulted in the formation of sapropels. The known sedimentary salt input is too low to be directly responsible for stagnation of the water column. However, once stagnation is initiated by other factors (e.g. decrease of excess evaporation), the extra salt input into the deep water will enhance the stagnation process. Therefore, the circulation mechanism may be more sensitive to external changes than assumed until now.