Advances in Earth Science
• Articles •
FENG Dong，CHEN Duo-fu. Barium Cycling in Pore Water of Seafloor Sediment: Indicator of Methane Fluxes[J]. Advances in Earth Science, 2007, 22(1): 49-57.
Methane and other hydrocarbons flux upward through deep-marine sediment may strongly impact the cycling of barium near the seafloor. Dissolved barium crossing sulfate-hydrocarbon transition (SHT) reacts with SO2-4, precipitating barium fronts composed of barite immediately above the SHT. During sediment burial, barite moves downward from SO2-4-rich to SO2-4-depleted pore water where it dissolves. In turn, Ba2+ dissolved diffuses upward from SO2-4-depleted to SO2-4-rich pore water where it precipitates as barite. In systems where upward Ba2+ diffusion exceeds downward barite burial, this barium cycling can result in a “barium front”, a short interval of anomalously high labile barium concentrations immediately above the depth of SO2-4-depletion. Because the depth of SHT is controlled by the fluxing of methane and other hydrocarbons, the fluxes of methane should be coupled with barium cycling. Thus “barium front” may become an indicator of present and past methane fluxing and can be used to reconstruct changes in the upward flux of methane. The methane and barium cycles in sediment pore water near the seafloor has been comprehensively reviewed. Moreover, the indicator of barium cycling to present and past gas seeping in sediment pore waters at seafloor has been discussed. Finally, the geological and geochemical characteristics of seep related barite have been summarized.