Speciation And Early Diagenesis Study Of Sulfur In The Sediments Of Jiaozhou Bay

Sulfur in marine sediments is an important participant in early diagenesis. Earlydiagenesis of sulfur exerts signigfcant influences on geochemical cycles of carbon, iron,phosphorus and a number of trace elements in marine sediments. Pyritic and organicsulfur (OS) are two important sulfur pools of solid-phase sulfur in marine sediments.Contents and isotope compositions of pyritic and organic sulfur are an important tool forbetter understanding the formation mechanism of pyrite, the sources and pathways of OS,the relationships between iron sulfide formation and diagenetic sulfurization of organicmatter (OM). In this study, two cores sediments were collected in the Jiaozhou Bay. Acombination of chemical extraction and sulfur isotopic compositions was used tocharacterize five sulfur pools: acid volatile sulfide (AVS), pyretic sulfur,non-chromium-reducible OS (non-CROS), humic acid sulfur (HA-S), and fulvic acidsulfur (FA-S). Twenty-three surface sediments were also collected in the bay forquantification HA-S, FA-S, pyritic sulfur, and residual organic sulfur (ROS). Foursediment samples were collected from four rivers surrounding Jiaozhou Bay and theYangtze River, respectively, and four surface sediments were collected from the EastChina Sea, for comparison of OS between river sediments and marine sediments. All theresults above together reactive iron were used for analysis. The main conclusions are asfollows:1. HA-S and non-CROS are dominated by biogenic OS, accounting for65~68%and67~77%, respectively, of total extracted OS, while FA-S is dominated bydiagenetic one (54~73%). In comparison with OS contents in coastal marinesediments of the world, human activities and waste inputs have not significantlyenhanced OS contents in Jiaozhou Bay.2. The study of sulfur isotopic compositions shows that humic sulfur andnon-CROS cannot fully reflect the bulk composition and origin of sediment.These two sulfur pools should be combined to better characterize the bulk composition and origin of OS.3. Iron sulfide formation and sulfurization of OM can coexist in the sediment profile,and both share the same limiting factors—the amount and reactivity OM. Ironsulfide formation has not competitively inhibited OM sulfurization to asignificant extent.4. The presence of pyrite at variable levels (2.836mol/g) in surface sedimentsindicate active bacterial sulfate reduction and rapid pyrite formation in thesubsurface layer. The spatial pattern of pyrite-S is strongly coupled to that ofsedimentary TOC, suggesting that OM reactivity is an important control on pyriteformation.5. The spatial distribution of FA-S is strongly coupled to that of TOC, suggestingthat diagenetic sulfurization of FA is largely controlled by enrichment of OM. ispoor spatial coupling between HA-S and TOC is probably due to low fraction ofdiag-OS in this OS pool. Residual OS is mainly from riverine inputs. The spatialcoupling among TOC, pyrite-S and FA-S can be used as a sensitive indicator ofanthropogenic impacts on benthic biogeochemistry of the bay.6. The contents of HA-S and FA-S in river sediments are comparable, and,regionally, do show no significant differences. OS in river sediments are mainlyresidual OS. Depositional environment, eutrophication state, and riverine inputscontaminant have led to higher average content of FA-S and HA-S in JiaozhouBay sediments than in the East China Sea sediment. HA-S content in marinesediments is only slightly higher than in riverine sediment. Much higher contentof FA-S in marine sediments than in riverine sediments can be ascribed todiagenetic sulfurization during early diagenesis in marine sediments.