Vitamin B1 in marine sediments: pore water concentration gradient drives benthic flux with potential biological implications

Vitamin B-1, or thiamin, can limit primary productivity in marine environments, however the major marine environmental sources of this essential coenzyme remain largely unknown. Vitamin B-1 can only be produced by organisms that possess its complete synthesis pathway, while other organisms meet their cellular B-1 quota by scavenging the coenzyme from exogenous sources. Due to high bacterial cell density and diversity, marine sediments could represent some of the highest concentrations of putative B-1 producers, yet these environments have received little attention as a possible source of B-1 to the overlying water column. Here we report the first dissolved pore water profiles of B-1 measured in cores collected in two consecutive years from Santa Monica Basin, CA. Vitamin B-1 concentrations were fairly consistent between the two years ranging from 30 pM up to 770 pM. A consistent maximum at 5 cm sediment depth covaried with dissolved concentrations of iron. Pore water concentrations were higher than water column levels and represented some of the highest known environmental concentrations of B-1 measured to date, (over two times higher than maximum water column concentrations) suggesting increased rates of cellular production and release within the sediments. A one dimensional diffusion-transport model applied to the B-1 profile was used to estimate a diffusive benthic flux of similar to 0.7 nmol m(-2) d(-1). This is an estimated flux across the sediment-water interface in a deep sea basin; if similar magnitude B-vitamin fluxes occur in shallow coastal waters, benthic input could prove to be a significant B-1-source to the water column and may play an important role in supplying this organic growth factor to auxotrophic primary producers.