Biomarkers in turbidites at ODP Sites 157-951 and 157-952@en

Free and ester-bound lipid biomarkers were analysed in oxidised and unoxidised parts of four distinct turbidites from the Madeira Abyssal Plain (MAP), which contained 1 to 2% organic carbon homogeneously distributed throughout the turbidites at the time they were deposited. These turbidites are well suited to study the effects of oxic degradation on lipid biomarkers without the complicating influence of varying organic matter sources, sedimentation rates, or bioturbation. One sample from the oxidised turbidite was compared with two samples from the unoxidised part of each turbidite. Postdepositional oxic degradation decreased concentrations of biomarkers by several orders of magnitude. The ester-bound lipids were degraded to a far lesser extent than their free counterparts were. The extent of degradation of different compounds differed substantially. Within a specific class of biomarkers, degradation also took place to a different extent, altering their distributions. This study shows that oxic degradation of the organic matter may have a profound effect on the biomarker fingerprint and may result in a severe bias in, for example, the interpretation of organic matter sources and the estimation of the palaeoproductivity of specific groups of phytoplankton.

本研究对采自马德拉深海平原（Madeira Abyssal Plain, MAP）的4套独立浊积岩（turbidites）的氧化与未氧化区段，开展了游离态与酯结合态脂质生物标志物分析。沉积阶段，这些浊积岩内均匀分布着占比1%~2%的有机碳。该类浊积岩非常适合用于探究有氧降解对脂质生物标志物的影响，且不受有机质来源、沉积速率或生物扰动等可变因素的复杂干扰。每份浊积岩的氧化区段取1个样品，未氧化区段取2个样品进行对照分析。沉积后有氧降解可使生物标志物的浓度降低数个数量级；酯结合脂质的降解程度远低于游离态脂质。不同化合物的降解程度存在显著差异；即便属于同一类生物标志物，其降解程度也有所不同，进而改变其组分分布格局。本研究表明，有机质的有氧降解会对生物标志物指纹图谱产生显著影响，并可能在有机质来源解译、特定浮游植物类群古生产力估算等研究中引入严重偏差。