Erosional Transfer of Sediment and Organic Carbon Through Time in the Kasaï Basin, Democratic Republic of the Congo

Abstract

African rainforests store large quantities of carbon within below‐ground reservoirs, yet these stocks are threatened by land use and climate disturbances. Previous studies revealed that the peatlands of the Cuvette Centrale in the Congo Basin accumulated less organic carbon (OC) between 7,500 and 2,000 yrs BP (so‐called “Ghost Interval”), likely caused by drier climate at this time and potentially linked to the “Late Holocene Rainforest Crisis” (LHRC)—a period of forest fragmentation around 3,000 yrs BP. This crisis event provides an ideal opportunity to reconstruct the effects of climatological and vegetational changes on OC burial rates in the Congo Basin using lake sediment records. To further constrain the spatial extent of the LHRC, we collected sediment cores from 10 lakes across the rainforest‐savanna boundary in the Kasaï Basin. We derived apparent sediment accumulation rates (SARs), which we with total organic carbon (TOC) and bulk density measurements to calculate apparent OC mass accumulation rates (OC MARs). Most lakes show a decrease in SAR during the LHRC, mirroring observations in existing cores from the peatlands of the Cuvette Centrale. The LHRC is thus likely a wider‐spread phenomenon than previously postulated, that is, not limited to central‐western Africa. Furthermore, OC mineral stabilization and thermal lability measurements on two representative lake records suggest that OC deposited over the last 5,000 cal yrs BP is highly susceptible to remineralization upon oxygen exposure. Our findings demonstrate the broad sensitivity of Congo Basin carbon stocks to precipitation patterns and land‐use change.