Vertical distributions of thiosulfate and sulfite in the Cariaco Basin

Water column profiles of S2O32- and SO32- were obtained in January and May 2004 in the eastern portion of the Cariaco Basin (10° 30ʹN 64°40ʹW). Mean concentrations in the chemocline (250 to 450 m) decreased from 2.3 (plus-minus) 1.1 (mu)mol L^-1 S2O32- in January to 1.4 (plus-minus) 0.3 (mu)mol L^-1 S2O32- in May and from 4.8 (plus-minus) 2.9 (mu)mol L^-1 SO32- in January to 2.7 (plusminus) 0.7 (mu)mol L^-1 SO32- in May. Integrated over this same depth interval, S2O32- was 459 mmol m^-2 in January and 287 mmol m^-2 in May and SO32- was 799 mmol m^-2 in January and 574 mmol m^-2 in May. During this time, the integrated chemoautotrophic production in the chemocline decreased from 26 to 13 mmol C m^-2 d^-1. The concurrent decreases in S2O32- and SO32- inventories and chemoautotrophic production are consistent with a decrease in the frequency or intensity of intrusion events. S2O32- and SO32were present in the oxic portion of the water column, suggesting lateral transport from shallower areas containing H2S. Calculations suggest that sufficient O2 and H2S can be supplied to the interface by advection and diffusion to form S2O32- in sufficient quantities to support the observed levels of chemoautotrophic production. However, apparently <2% of the H2S needed to form the observed amount of S2O32- can be produced from the degradation of organic carbon sinking through the interface at this site. This suggests either that the H2S or carbon flux must be supplied laterally, perhaps from shallower areas (not yet sampled), or that chemoautotrophic production near the interface is overestimated.