Recent terrestrial and carbonate fluxes in the pelagic eastern Mediterranean: a comparison between sediment trap and surface sediment

A sediment trap mooring was deployed in the central eastern Mediterranean from November 1991 to August 1994. At 3000 m water depth, total mass, Al, Ca, Mg, Sr and 230Th fluxes recovered by the sediment trap are highly seasonal, with highest fluxes during early spring in 1992 and 1993, and during late-spring/early-summer in 1994. Comparison of historic annual satellite-derived chlorophyll records (coastal zone colour scanner) with the trap flux time series indicates a lag of 4–6 months between maximum primary production in the surface ocean and maximum flux recorded by the trap. Only the flux of coccospheres to the trap is at a maximum ~1 month after maximum pigment concentrations in surface waters, a value commonly found in other areas. Quantification of the inorganic (lithogenic) flux to the trap indicates that Saharan dust is likely to be the major contributor to the trap mass flux. The trapping efficiency of the sediment trap, as calculated from the intercepted 230Th flux, is only 23%, and the trap Al-flux is similarly ×4 lower than Al fluxes measured in nearby uppermost sediments. Compared with surface sediments, the trap-intercepted carbonate fluxes are even lower (×9) than the corresponding lithogenic fluxes. This is partly due to the very low abundance of large (>32 m) foraminifera and pteropods found in the trap material compared to the surface sediment. We speculate that the period of our sediment trap deployment was insufficiently long to recover episodical large fluxes, such as may be triggered by North Atlantic Oscillation variations.