Response to comment on “The conundrum between chemoautotrophic production and reductant and oxidant supply: A case study from the Cariaco basin”

Abstract

Jost (in press) argued that our measured chemoautotrophic production is overestimated due to methodology and that oxygen contamination is the most likely explanation for the energy conundrum. We have endeavored to minimize atmospheric exposure from sample collection through incubation since the CARIACO program began. We have also intentionally added headspaces to examine the aeration effect and found that, if anything, oxygen contamination appears to suppress 14C fixation rates at the depths of interest. Even if trace oxygen contamination occurs during sample preparation and incubation, we do not believe that could explain the 800 to1600-fold difference between the chemoautotrophic production and the reactant supply using stoichiometry based on lab cultures of sulfide oxidizers. In Li et al. (2012), the stoichiometry we used does not violate any thermodynamic laws. Thus the value we used, while probably on the high side, is theoretically possible. We argue that production of sulfide within the redoxcline may be a significant source based on the fact that a large fraction of the organic matter produced by the chemoautotrophs within the redoxcline does not seem to settle into underlying sediment traps. Our main intention was to propose that in situ sulfide production, i.e., a “cryptic sulfur cycle”, within the redoxcline might be a significant, but neglected process.