Graduation date: 2007Large barite (BaSO4) structures mark cold seeps in the southern San Clemente Basin. Barium flux to San Clemente sediments is two to three times greater than fluxes measured in surrounding California Borderland basins. Analyses of sediment trap material, water column samples, sediments and pore water indicate that expected bariumbearing mineral phases (e.g. detrital aluminosilicates, biogenic material and Fe/Mn oxyhydroxides) cannot account for excess barium accumulating in the San Clemente Basin. This excess represents 7-70 % by weight of total sedimentary barium. Cold seep barite is accumulating in San Clemente sediments at an average rate of approximately 11 μmol m-2 day-1, a value that is comparable to the combined flux of detrital and biogenic material to the basin floor. Cold seep barite is largely unaccounted for in sedimentary barium inventories. The magnitude of cold seep barite flux to San Clemente Basin sediments and the occurrence of cold seeps throughout the oceans necessitate consideration of this phase in the development of barium geochemical budgets and the variety of paleoproxies involving barium in marine sediments.