Vast, overlooked peat, and organic soils in Brazil's Cerrado: carbon storage, dynamics, and stability.

Tropical peatlands are critical for climate mitigation due to their dual role as major carbon sinks and methane sources. In rainforests, high and stable rainfall supports peat accumulation in tropical climates. However, groundwater-fed peatlands in seasonally dry tropical ecosystems remain poorly understood, despite their potential importance in global carbon dynamics. Here, we present an integrated carbon assessment in organic soil ecosystems (locally known as Veredas and Campos úmidos) in the Brazilian savanna. We quantified carbon in soil and biomass, dated carbon using radiocarbon, and evaluated chemical stability using infrared spectrometry. We used machine learning models to map their potential area. Additionally, we measured soil CO2 and CH4 efluxes to evaluate the influence of climatic seasonality on emissions. Veredas contained exceptionally high carbon stocks (c. 1200 Mg C ha-1) accumulated over c. 20 000 yr and spanning c. 16.7 Mha. However, spectroscopy indicated low carbon stability compared to other tropical peatlands, and c. 70% of annual CO2 and CH4 emissions occurred during the dry season. Our findings show that the Brazilian Cerrado harbors one of the largest carbon-storing ecosystems in the tropical Americas, yet one that is highly vulnerable to land-use change and intensified drought. Despite their wide distribution, peat accumulation and the extent of Veredas remain uncertain.