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To achieve more accurate Earth system model projections of diverse climate scenarios, researchers need observation-based data on the movement of carbon between reservoirs, and especially across tropical regions. The Tropical Low-Pressure Belt (TLPB) is a key driver of atmospheric circulation across lower latitudes. While the TLPB shifts across the east–west extent of northern Africa, the extent to which 14C concentrations apply to Afrotropical forests remains untested, restricting our understanding about other carbon feedbacks. Here, we present a high-precision atmospheric 14C record (1940–2012) from a lowland tropical tree species (Entandrophragma utile) in Cameroon. We included 107 measurements from whole rings and 15 intra-annual slices. The intra-annual 14C data from 1962, 1963, and 1964 confirm a 7-month long growing season (April–November) with a photosynthetic profile typical of Northern Hemisphere (NH) sites, and showing no nonstructural-carbohydrate interference. The full 14C record reveals that air masses reaching the site were derived primarily from Southern Hemisphere (SH) readings followed by recycled bomb-14C signals from soil and litter. Radiocarbon results were substantiated by HYSPLIT model trajectories coupled with NCEP/NCAR reanalysis data. The paradox of finding that tropical NH trees grow using 14CO2 of SH air masses and land-surface respiration challenges existing zonal 14C classifications. Our findings highlight an essential role for robust observational 14C data in refining atmospheric models and improving carbon-cycle assessments across distinct climate zones. 

To achieve more accurate Earth system model projections of diverse climate scenarios, researchers need observation-based data on the movement of carbon between reservoirs, and especially across tropical regions. The Tropical Low-Pressure Belt (TLPB) is a key driver of atmospheric circulation across lower latitudes. While the TLPB shifts across the east–west extent of northern Africa, the extent to which 14C concentrations apply to Afrotropical forests remains untested, restricting our understanding about other carbon feedbacks. Here, we present a high-precision atmospheric 14C record (1940–2012) from a lowland tropical tree species (Entandrophragma utile) in Cameroon. We included 107 measurements from whole rings and 15 intra-annual slices. The intra-annual 14C data from 1962, 1963, and 1964 confirm a 7-month long growing season (April–November) with a photosynthetic profile typical of Northern Hemisphere (NH) sites, and showing no nonstructural-carbohydrate interference. The full 14C record reveals that air masses reaching the site were derived primarily from Southern Hemisphere (SH) readings followed by recycled bomb-14C signals from soil and litter. Radiocarbon results were substantiated by HYSPLIT model trajectories coupled with NCEP/NCAR reanalysis data. The paradox of finding that tropical NH trees grow using 14CO2 of SH air masses and land-surface respiration challenges existing zonal 14C classifications. Our findings highlight an essential role for robust observational 14C data in refining atmospheric models and improving carbon-cycle assessments across distinct climate zones. 

To ensure unbiased tree-ring radiocarbon (14C) results, traditional pretreatments carefully isolate wood cellulose from extractives using organic solvents, among other chemicals. The addition of solvents is laborious, time ­consuming, and can increase the risk of carbon contamination. Tropical woods show a high diversity in wood­ anatomical and extractive composition, but the necessity of organic-solvent extraction for the 14C dating of these diverse woods remains untested. We applied a chemical treatment that excludes the solvent step on the wood of 8 tropical tree species sampled in South-America and Africa, with different wood-anatomical and extractive properties. We analyzed the success of the extractive removal along with several steps of the a-cel­lulose extraction procedure using Fourier Transform Infrared (FTIR) spectroscopy and further confirmed the quality of 14C measurements after extraction. The ex-cellulose extracts obtained here showed FTIR-spectra free of signals from various extractives and the 14C results on these samples showed reliable results. The chemical method evaluated reduces the technical complexity required to prepare a-cellulose samples for 14C dating, and therefore can bolster global atmospheric 14C applications, especially in the tropics.