Methane and hydrogen sulfide in porewater of sediment cores from the upwelling area off Namibia

Porewater concentrations of sulfate, methane, and other relevant constituents were determined on four sediment cores from the high productivity upwelling area off Namibia which were recovered from the continental slope at water depths of 1300 and 2000 m. At all four stations a distinct sulfate-methane transition zone was observed several meters below the seafloor in which both sulfate and methane are consumed. Nutrient porewater concentration profiles do not show gradient slope changes at the depths of the transition zones. Flux calculations carried out on the basis of the determined porewater profiles revealed that anaerobic methane oxidation accounts for 100% of deep sulfate reduction within the sulfate-methane transition zone and consumes the total net diffusive sulfate flux. A significant contribution of organic carbon oxidation to the reduction of sulfate at these depths could, therefore, be excluded. […]

在纳米比亚高生产力上升流区域的海底1300米和2000米深度处回收的四段沉积岩心样本中，检测了硫酸盐、甲烷及其他相关成分的孔隙水浓度。在所有四个站位，均在海底数米以下观察到明显的硫酸盐-甲烷过渡带，该区域内硫酸盐和甲烷均被消耗。营养物孔隙水浓度剖面在过渡带深度并未显示出梯度斜率的变化。基于所确定的孔隙水浓度剖面进行的通量计算揭示，厌氧甲烷氧化在硫酸盐-甲烷过渡带中负责了深部硫酸盐还原的100%，并消耗了总净扩散硫酸盐通量。因此，可以排除在这些深度有机碳氧化对硫酸盐还原有显著贡献的可能性。