Total phospholipid fatty acid concentrations structrures of ODP Hole 191-1179 samples (Table 1)

Sediment samples ranging from 0.05 to 278 m below sea floor (mbsf) at a Northwest Pacific deep-water (5564 mbsl) site (ODP Leg 191, Site 1179) were analyzed for phospholipid fatty acids (PLFAs). Total PLFA concentrations decreased by a factor of three over the first meter of sediment and then decreased at a slower rate to approximately 30 mbsf. The sharp decrease over the first meter corresponds to the depth of nitrate and Mn(IV) reduction as indicated by pore water chemistry. PLFA-based cell numbers at site 1179 had a similar depth profile as that for Acridine orange direct cell counts previously made on ODP site 1149 sediments which have a similar water depth and lithology. The mole percentage of straight chain saturated PLFAs increases with depth, with a large shift between the 0.95 and 3.95 mbsf samples. PLFA stable carbon isotope ratios were determined for sediments from 0.05 to 4.53 mbsf and showed a general trend toward more depleted d13C values with depth. Both of these observations may indicate a shift in the bacterial community with depth across the different redox zones inferred from pore water chemistry data. The PLFA 10me16:0, which has been attributed to the bacterial genera Desulfobacter in many marine sediments, showed the greatest isotopic depletion, decreasing from -20 to -35 per mil over the first meter of sediment. Pore water chemistry suggested that sulfate reduction was absent or minimal over this same sediment interval. However, 10me16:0 has been shown to be produced by recently discovered anaerobic ammonium oxidizing (anammox) bacteria which are known chemoautotrophs. The increasing depletion in d13C of 10me16:0 with the unusually lower concentration of ammonium and linear decrease of nitrate concentration is consistent with a scenario of anammox bacteria mediating the oxidation of ammonium via nitrite, an intermediate of nitrate reduction.

本研究对西北太平洋深水站位的0.05~278 mbsf（海底以下米数，meters below sea floor）沉积物样品开展了磷脂脂肪酸（phospholipid fatty acids, PLFAs）分析。该站位水深达5564 mbsl（海平面下米数，meters below sea level），为大洋钻探计划（Ocean Drilling Program, ODP）第191航次1179站位。总PLFA浓度在沉积物上层1米内下降至初始的1/3，随后以更缓慢的速率衰减至约30 mbsf处。上层1米内的浓度骤降与孔隙水化学数据指示的硝酸盐及四价锰还原带深度相吻合。1179站位基于PLFA的细胞数深度分布，与此前在水深、岩性相似的大洋钻探计划1149站位沉积物中开展的吖啶橙直接细胞计数（Acridine orange direct cell counts）结果具有高度相似性。直链饱和PLFAs的摩尔百分比随深度增加而升高，在0.95~3.95 mbsf的样品间出现显著变化。研究人员对0.05~4.53 mbsf的沉积物完成了PLFA稳定碳同位素比值测定，结果显示整体随深度增加呈现δ¹³C值愈发贫化的趋势。上述两项观测结果均表明，基于孔隙水化学数据推断的不同氧化还原带内，细菌群落随深度发生了演替。PLFA标志物10me16:0曾被归因于众多海洋沉积物中的脱硫杆菌属（Desulfobacter），但其同位素贫化程度最高，在沉积物上层1米内从-20‰降至-35‰。孔隙水化学数据显示，同一沉积层段内硫酸盐还原作用缺失或极微弱。然而已有研究证实，10me16:0可由新近发现的厌氧氨氧化（anaerobic ammonium oxidizing, anammox）细菌合成，这类细菌属于化能自养菌（chemoautotrophs）。10me16:0的δ¹³C值随深度愈发贫化，同时伴随异常偏低的铵盐浓度与硝酸盐浓度的线性下降，这与厌氧氨氧化细菌通过硝酸盐还原中间体亚硝酸盐介导铵氧化的作用机制相符。