Plant-wax n-alkanes from the central Congo Basin as palaeo-environmental and -climatic proxies

2026

Article référencé dans le Web of Science WOS:001636197500001

Guardiola M., Bouka G. U. D., Abaye C., Menges J., Rostek F., Leduc G., Bard E., Schefuss E., Garcin Yannick

Organic Geochemistry, 2026, 212, 105092 [17 p.] ISSN 0146-6380

The central Congo Basin is home to the world's largest tropical peatland complex and is covered with swamp forest. In the face of climate change and future human activities in the region, it is important to understand the factors that determine the nature and dynamics of the peatland vegetation cover. One way to gain insight into these factors is to reconstruct the history of the central Congo Basin peatlands. Analysing lipid biomarkers extracted from peat cores such as plant wax n-alkanes enables past environmental and climatic conditions to be reconstructed. However, there is currently no information on how the production of plant waxes by different plant species influences the abundance and isotopic composition of n-alkanes in peat and other archives in the Congo Basin. In this study we analysed plant wax n-alkane abundances, delta C-13 and delta D values according to photosynthetic pathways (C-3 vs. C-4), angiosperm subclasses (dicotyledons vs. monocotyledons), and source water delta D values in the dominant plant types (trees, shrubs, and herbs) in the peatland area of the Cuvette Department in the Republic of the Congo. Our dataset enables the definition of a new n-alkane distribution index, named GRIND, that distinguishes between C-3 (mostly dicotyledons) and C-4 (monocotyledons) plants as follows: (n-C-27 + n-C-33 + n-C-35)/(n-C-25 + n-C-27 + n-C-29 + n-C-31 + n-C-33 + n-C-35). This index may therefore be used to analyse Central African peat deposits and derive the relative abundance of C-3 and C-4 plant waxes in the past, independently of delta C-13 measurements. Furthermore, delta C-13 values from the central Congo Basin and other African sites suggest that environments with high relative humidity (> 80%) are characterised by very negative delta C-13 values (i.e., < -37 parts per thousand) of n-C-29 and n-C-31 alkanes. This observation highlights the potential of n-alkane delta C-13 in deriving climatic information under high relative humidity conditions in Central African lowlands, and contribute to palaeo-climatic reconstructions. Finally, the delta D values of n-C-29 and n-C-31 alkanes demonstrate that, despite contrasting apparent fractionation values associated with photosynthetic pathways and plant functional types - which can be accounted for using delta C-13 and pollen data in sedimentary deposits - they reliably reflect the delta D of environmental water. This confirms that plant wax n-alkane delta D values are effective tools for reconstructing palaeo-climatic changes in equatorial regions.

Sciences du milieu [021] ; Géologie et formations superficielles [064] ; Sciences du monde végétal [076] ; Etudes, transformation, conservation du milieu naturel [082]

Fonds IRD [F B010095902]

fdi:010095902