Tropical Central African bomb radiocarbon reveals antiphase air-mass atmospheric fluxes and vegetation-growth relationships

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.