Ž . Marine Chemistry 69 2000 19–31 www.elsevier.nlrlocatermarchem Marine barite and celestite saturation in seawater Ahmed I. Rushdi a,b , James McManus c, ) , Robert W. Collier a a College of Oceanic and Atmospheric Science, Oregon State UniÕersity, 104 Ocean Admin. Building, CorÕallis, OR 97331-5503, USA b Department of Oceanography, Faculty of Science, Sana’a UniÕersity, Sana’a, Yemen c Large Lakes ObserÕatory, UniÕersity of Minnesota, 10 UniÕersity Dr., Duluth, MN 55812, USA Received 23 July 1998; accepted 18 August 1999 Abstract The stoichiometric solubility product, K U , of barite and celestite in seawater has been calculated using thermodynamic sp,T constants, K , and the activity coefficients for barium, strontium, and sulfate in seawater. An equation of the form: s0 C U n ln K sA qB lnT q qDS sp,T T Ž . has been used. The constants A, B, C, D and n are derived from the calculated stoichiometric or total solubility product of Ž . barite and celestite in seawater as a function of temperature and salinity. T is the absolute temperature K and S is the salinity. The effect of pressure on K U is also calculated. Comparing the solubility products determined from this equation sp,T and the pressure effect equation to the distribution of Ba, Sr and SO in seawater, we conclude that the upper surface water 4 w of the Southern Ocean is likely supersaturated with respect to pure barite, in agreement with Jeandel et al. Jeandel, C., Dupre, B., Lebaron, G., Monnin, C., Minster, J.F., 1996. Longitudinal distributions of dissolved barium, silica and alkalinity x w in the western and southern Indian Ocean. Deep-Sea Res. 43, 1–31. and Monnin et al. Monnin, C., Jeandel, C., Cattaldo, x T., Dehairs, F., 1999. The marine barite saturation state of the world oceans. Mar. Chem. 65, 253–261. and that the oceanic water column is typically -30% saturated with respect to celestite. The model, which includes the thermodynamic solid–solution behavior of barite in seawater at 258C and 1 atm, suggests that this mineral may contain up to 13 mol% SrSO at equilibrium. Accordingly, we have determined the stoichiometric solubility products of strontian barite as a 4 function of salinity and temperature: 15421 X Ba 0.3 ln K s247.88 y38.333lnT y q1.27S sp T Using our model results for the total solubility product of the Sr-barite phase and seawater Ba and SO concentration data, 4 we conclude that the maximum saturation level of the oceans with respect to marine barite is 63% in the North Atlantic, 88% in the Indian Ocean, and 111% in the North Pacific. The depth of this maximum saturation level is shallower in the Atlantic ) Corresponding author. Tel.: q 1-218-726-7384; E-mail: jmcmanus@d.umn.edu 0304-4203r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0304-4203 99 00089-4