ORACLE

Tropical terrestrial ecosystems are highly productive and constitute a critical component of the global carbon cycle. The Congo Basin, the second largest river basin on Earth, accommodates extensive swamp forests in its central part, known as the “Cuvette Centrale Congolaise”. Peat accumulation associated with these swamp forests represents a major below-ground carbon reservoir of global importance. The recent description and mapping of these peatlands calls for further research efforts to understand the history of these sensitive ecosystems to better predict their vulnerability with respect to future climate and land-use changes. The collaborative and international project ORACLE will focus on the environmental evolution of the peatlands in the Cuvette Centrale Congolaise. Carbon storage in peatlands depends on a permanently high water table, which in the tropics is maintained by high rainfall frequency. An increase in drought frequency/rainfall seasonality has been predicted to lower/stop carbon storage. Still largely unaffected by human activities, these peatlands are considered highly susceptible to hydrocarbon exploration, logging, drainage, agriculture, and other forms of disturbance that could significantly affect them: their disturbance, under the combined effects of deforestation and drier climatic conditions, could result in massive CO2 emissions into the atmosphere. ORACLE proposes to reconstruct the history of the peatlands of the Cuvette Centrale Congolaise to (i) better understand a key region of the Holocene carbon cycle in the tropics, (ii) provide a detailed record of regional peat accumulation/loss during the Holocene, and (iii) resolve the drivers (natural and anthropogenic) of changes in these ecosystems. To address these issues, we plan to collect and analyze peat cores in the Republic of Congo by combining classical carbon-accumulation determinations with novel molecular and isotopic techniques, such as dD, d13C, and D14C of lipid biomarkers derived from terrestrial higher plants together with analysis of peat-derived branched glycerol dialkyl glycerol tetraether membrane lipids (GDGTs) and palynology to assess ecosystem changes. These analyses will be flanked by an archaeological survey and dating of artefacts. This pluridisciplinary approach will allow reconstructing the history of peat accretion/loss, hydroclimate, vegetation cover, temperature, pH, and human activity. The results from ORACLE will help to better predict the vulnerability of the Cuvette Centrale Congolaise ecosystems facing climate change and human activity. They will be highly valuable for paleo-ecologists and paleo-climatologists, including climate modellers, to better understand the Holocene climatic and ecological evolution of Central African ecosystems. Unravelling the effects of past climate changes and, potentially, human activities on the structure and composition of wetland vegetation and carbon cycling are needed to improve conservation strategies.