pH is one of the major parameters governing peat functioning, and pH variations in modern peatlands affect carbon and methane production and consumption. Paleo-pH reconstructions have been limited thus far, but they could help to better understand peat functioning in variety of settings and also serve as an indirect proxy for climatic and environmental variations such as precipitation. Bacterial hopanes and branched Glycerol Dialkyl Glycerol Tetraethers (brGDGTs) were investigated in a 10-ka peat record from North-East Cameroon (NGaoundaba, Western Central Africa). Recently developed pH proxies using the hopane ββ/(αβ + ββ) ratio and the brGDGT cyclization ratio (CBT) were applied and compared with previously published bulk organic data from the same core. Different hypotheses are usually proposed to explain the high abundance of the “thermally mature” C αβ hopane in peats: acid-catalyzed isomerization of ββ to αβ isomers with or without biological mediation or the direct input of C αβ hopanes by bacteria. In the NGaoundaba peat deposit, the opposite variation in the ββ/(αβ + ββ) ratio of C and C hopanes and the carbon isotopic composition of C ββ and αβ hopanes suggest that an eventual transformation of C ββ to αβ isomers is not possible without biological mediation. A linear correlation between hopane- and brGDGT-reconstructed pH is observed, suggesting a similar response to environmental changes for these two independent proxies. A large increase in reconstructed pH values coincides with changes in vegetation and precipitation at the end of the African Humid Period (AHP). Lower pH values are observed during the AHP, coinciding with a period of increased precipitation and consistent with bulk organic data and slightly higher C ββ hopane δC values compared to middle and late Holocene. Bulk organic data indicate an interruption of the AHP by a drier intermission that coincides with a decrease in reconstructed pH values, probably reflecting a decrease in evapotranspiration. Variations in pH values could be interpreted in terms of preservation of peat organic matter and might reflect past changes in methane cycling in the investigated peatland. The present study reinforces the idea that reconstruction of pH in peat deposits represents a promising proxy of environmental change, enabling a better understanding of changes in peat functioning over large timescales and various locations.

中文翻译：

---

对藿烷和 brGDGT 作为泥炭 pH 值代理的限制

pH 值是控制泥炭功能的主要参数之一，现代泥炭地的 pH 值变化会影响碳和甲烷的产生和消耗。迄今为止，古 pH 值重建还很有限，但它们可以帮助我们更好地了解泥炭在各种环境下的功能，也可以作为气候和环境变化（如降水）的间接代表。在喀麦隆东北部（非洲中西部 NGaoundaba）的 10-ka 泥炭记录中对细菌藿烷和支链甘油二烷基甘油四醚 (brGDGT) 进行了研究。应用最近开发的使用藿烷 ββ/(αβ + ββ) 比率和 brGDGT 环化比率 (CBT) 的 pH 代理，并与之前发布的来自同一岩心的大量有机数据进行比较。通常提出不同的假设来解释泥炭中“热成熟”C αβ 藿烷的高丰度：在有或没有生物介​​导的情况下，ββ 酸催化异构化为 αβ 异构体，或者细菌直接输入 C αβ 藿烷。在 NGaoundaba 泥炭矿床中，C 和 C 藿烷的 ββ/(αβ + ββ) 比率以及 C ββ 和 αβ 藿烷的碳同位素组成的相反变化表明，如果没有生物介导。观察到藿烷和 brGDGT 重建 pH 值之间的线性相关性，表明这两个独立代理对环境变化的响应相似。重建 pH 值的大幅增加与非洲湿润期 (AHP) 末期植被和降水的变化同时发生。在 AHP 期间观察到较低的 pH 值，与降水增加的时期一致，与大量有机数据一致，与全新世中晚期相比，C ββ 藿烷 δ13C 值略高。大量有机数据表明 AHP 因干燥间歇期而中断，这与重建 pH 值的下降同时发生，可能反映了蒸散量的减少。 pH 值的变化可以从泥炭有机质的保存角度来解释，并且可能反映了所调查泥炭地甲烷循环的过去变化。本研究强化了这样的观点，即泥炭沉积物 pH 值的重建代表了环境变化的一个有前景的指标，使人们能够更好地了解泥炭在大时间尺度和不同地点功能的变化。