Environmental and climatic evolution of a river-proximal peatland in the Cuvette Centrale, Congo Basin

Tropical peatlands play a crucial role in the global carbon cycle, yet their formation and response to environmental changes remain poorly understood. The Congo Basin, containing the World's largest tropical peatlands, holds about 30 billion tons of carbon in the Cuvette Centrale. Initial studies revealed diverse peat deposits in different geomorphic and hydrologic settings, with extensive peat domes in interfluvial basins and river-proximal peatlands following hydrographic networks. Here, we present a comprehensive analysis of a peat core from a peatland in close vicinity of the Momboyo River within the Cuvette Centrale. Using bulk organic carbon and nitrogen analyses, Rock-Eval® thermal analysis, and plant wax carbon and hydrogen isotope compositions, we reconstructed this peatland's evolution and associated past hydroclimatic conditions. Our findings reveal distinct phases of peat accumulation, transitioning from an organic carbon-rich river floodplain to a forested marshland, and finally to a closed-canopy swamp forest. Rock-Eval® parameters indicate in-situ peat accumulation in the marshland and swamp forest phases. Peat initiation occurred around 10.6 calibrated kiloanni before present (cal ka BP) under increasing precipitation and around 8.7 cal ka BP the terrestrialization of the peatland coincided with the establishment of a closed canopy forest. Notably, we also identify a trend to drier climatic conditions from 5 cal ka BP onwards and the previously described “Ghost Interval” – an interval of heavily decomposed peat – in this core, indicating this period left its mark across peatlands in different parts of the Cuvette Centrale. Last, a short-lived vegetation change occurred between 1.7 and 1.5 cal ka BP that did not impact peat formation. Regarding the climatic evolution, the plant wax hydrogen isotope (δD n -C29 ) record corroborates regional climatic patterns observed in previous studies, emphasizing the close linkage between precipitation regimes and peatland development. The strong agreement between our findings and a δD n -C29 record from the offshore Congo fan further supports the regional nature of climatic evolution. • River-proximal peat core reveals 10.6 kyr of peatland evolution in Cuvette Centrale. • Setting evolved from floodplain over forested marshland to swamp forest peatland. • Plant wax hydrogen isotopes confirm link of precipitation and peatland development. • Drier climate trend began ∼5 cal ka BP, marked by "Ghost Interval" of decomposed peat. • Regional climate patterns align with findings from the offshore Congo fan.