White Paper Title: 
Sulfur speciation in the diffuse flow zones of Lau Basin

Using in-situ electrochemical sensors, we mapped the temperature, oxygen, H2S, partially oxidized sulfur species, as well as FeS and Fe2+ in the diffuse flow environments of Lau Basin, in coordination with macrofaunal mapping done by Chuck Fisher’s group. We can now compare changes in all of these chemical species from 2006 to 2009, using the more than 10,000 scans from each cruise. Trends in diffuse flow chemistry can also be viewed in comparison to the high temperature focused flow chimneys from the same vent sites. For example, sulfide to temperature ratios for the diffuse flow zones exhibit little change from 2006 to 2009, while for focused flow, the sulfide significantly decreased. Average temperature for some diffuse flow zones has increased while the S to T ratio remains constant, indicating greater overall sulfide from some sites, in contrast with lower temperature and lower sulfide from focused flow sites.  Additionally, the partially oxidized sulfur species thiosulfate and polysulfides have been measured. These partially oxidized sulfur species are not temporally stable and so can only be detected using in- situ techniques. The concentrations of these oxidized S species directly correlate with the concentration of H2S at a given site.

Comparison to EPR integrated study site

The partially oxidized sulfur species, thiosulfate and polysulfides, have both been detected in significant quantities at Lau Basin. In similar diffuse flow studies conducted at EPR 9oN, these species were identified, but in insignificant quantities. Possible explanations for the difference between Lau Basin and EPR are the presence of distinct fauna, and/or the presence of a more oxidized substrate at Lau Basin. Evidence for either of these possibilities in determining the difference in speciation between the sites will be explored, as well as differences found from North to South at Lau Basin.