The marine barite saturation state of the world's oceans

This paper addresses the question of the eventual control of barium concent ration in seawater by an equilibrium with barite. For this, we have used a new thermodynamic model to compute the barite saturation index of ocean wat ers, mainly from GEOSECS data. Our results show that equilibrium between ba rite and seawater is reached in a number of places: cold surface waters of the Southern Ocean, waters at intermediate depths (2000-3500 m) in the Paci fic, deep waters (2000-3500 m) of the Gulf of Bengal. The only samples for which a slight barite supersaturation is found are the surface waters at GE OSECS station G89 in the Weddell Gyre. Besides these locations, the rest of the world's oceans is undersaturated, as was established by Church and Wol gemuth [Church, T.M., Wolgemuth, K., 1972. Marine barite saturation, Earth Planet. Sci. Lett. 15 35-44.]. There is a return to undersaturation of the water column at depths of about 3500 m in the Pacific and of about 2500 m i n the Southern Ocean. The reverse is found for GEOSECS station 446 in the G ulf of Bengal for which the highest Ba concentrations can be found at depth : surface waters are undersaturated and equilibrium is reached below 2000 m . Finally, we briefly discuss the role of biogenic and inorganic processes on barite formation in the ocean as well as the influence of strontium subs titution in marine barites. (C) 1999 Elsevier Science B.V. All rights reser ved.