New studies conducted by an international team under the leadership of scientists from South China Sea Institute of Oceanology (SCSIO), Chinese Academy of Sciences have found time integrated variation of sources of fluids, seepage dynamics, and mechanisms of trace metal enrichment archived in authigenic carbonate from cold hydrocarbon seeps.

　　Careful examination has revealed the diversity of stable carbon and oxygen isotopes, and mineral compositions in MC118 carbonates. The study also found that biomarker patterns of methanotrophs and methanogens preserved in seep carbonates.Such diversities were interpreted to reflect changes in seepage flux and in the composition of seepage fluids over time. The findings suggest that methane production at seeps, an environment typified by anaerobic oxidation of methane, might be a common, yet sometimes overlooked process.

　　

　　

　　Figure 1.Relative percentages of glycerol dibiphytanyl glycerol tetraethers (GDGT) in three carbonate samples from MC118 (Gulf of Mexico).(Image by SCSIO)

　　

　　Recent work on seep carbonates revealed variable Ce anomalies and anomalous enrichments of certain trace metals. However, the mechanisms accounting for such anomalies remain poorly constrained. Researchers from SCSIO found that the covariation of Mo with U, including authigenic Mo and U enrichments proved useful to obtain new insight into the applicability of Ce anomalies to constrain past redox conditions. The study also found that iron oxyhydroxides played an important role in the adsorption of Mo, As, and Sb in the water column and theirtransfer to the sediment. Similar processes and scenarios may apply to other modern and fossil cold seep sites.

　　

　　

　　Figure 2.Schematic diagramillustrating the adsorption and transportation process of Mo, As, and Sb and MREE. (Image by SCSIO)

　　

　　The results have been published in Chemical Geology.The research was supported by the “Hundred Talents Program” of Chinese Academy of Sciences and National Natural Science Foundation of China.

　　

　　References:

　　(1) Feng D, Birgel D, Peckmann J, Roberts HH, Joye SB, Sassen R. Liu X-L, Hinrichs K-U, Chen DF, 2014. Time integrated variation of sources of fluids and seepage dynamics archived in authigenic carbonates from Gulf of Mexico Gas Hydrate Seafloor Observatory. Chemical Geology 385, 129-139.

　　(2) Hu Y, Feng D, Peckmann J, Roberts HH, Chen DF, 2014. New insights into cerium anomalies and mechanisms of trace metal enrichment in authigenic carbonate from hydrocarbon seeps. Chemical Geology 381, 55-66.