Vertical distributions of thiosulfate and sulfite in the Cariaco Basin

Water column profiles of S₂O₃^2- and SO₃^2- were obtained in January and May 2004 in the eastern portion of the Cariaco Basin (10°30'N 64°40'W). Mean concentrations in the chemocline (250 to 450 m) decreased from 2.3 ± 1.1 μmol L ^-1 S₂O₃^2- in January to 1.4 ± 0.3 μmol L^-1 S₂O₃^2- in May and from 4.8 ± 2.9 μmol L^-1 SO₃^2- in January to 2.7 ± 0.7 μmol L^-1 SO₃^2- in May. Integrated over this same depth interval, S₂O ₃^2- was 459 mmol m^-2 in January and 287 mmol m^-2 in May and SO₃^2- 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 S ₂O₃^2- and SO₃^2- inventories and chemoautotrophic production are consistent with a decrease in the frequency or intensity of intrusion events. S₂O₃ ^2- and SO₃^2- were 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 S₂O₃^2- in sufficient quantities to support the observed levels of chemoautotrophic production. However, apparently <2% of the H₂S needed to form the observed amount of S ₂O₃^2- 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.