THE INTERFACE BETWEEN OXIC SEAWATER AND THE ANOXIC BANNOCK BRINE - ITS SHARPNESS AND THE CONSEQUENCES FOR THE REDOX-RELATED CYCLING OF MN AND BA

The interface oxic seawater/anoxic brine at a depth of 3330 dbar in the Bannock Basin (eastern Mediterranean), has been sampled in great detail using the Interface Sampler. This instrument, mounted on and triggered by the CTD/rosette system, has allowed us to take up to ten 50-ml samples every 10 cm (ABC cruise) or every 30 cm (BAMO-3 cruise) in the water column near the interface. The change from seawater to brine takes place in an interval of < 230 cm, which is the most dramatic interface of this kind ever reported for the deep marine environment. At the interface, the redox cycling of manganese takes place at a slightly shallower depth than for sulphur. The concentration of Ba near the interface appears to be determined mainly by its association with the redox cycling of Mn, whereas in the brine it is determined by its equilibrium with respect to barite (BaSO4). © 1990.