Cryptic carbon: The hidden carbon in forested wetland soils

Abstract Inland wetlands are critical carbon reservoirs storing 30% of global soil organic carbon (SOC) within 6% of the land surface. However, forested regions contain SOC-rich wetlands that are not included in SOC maps, which we refer to as ‘cryptic carbon’. To demonstrate the magnitude of cryptic carbon, we map SOC as a function of a continuous, upland-to-wetland gradient across a large catchment. Total catchment SOC was comparable to global SOC maps but wetlands delineated by our approach contained 1.7 ± 0.3 TgC compared to 0.3 ± 0.2 TgC in currently mapped wetland SOC. Cryptic carbon, the wetland SOC outside of currently available maps, was 1.5 ± 0.3 TgC or 383% higher than the current estimates. When combined, the new total wetland SOC including cryptic carbon increased to 1.8 TgC ± 0.5 or by 483%, highlighting vast stores of SOC are not mapped and contained in unprotected and vulnerable wetlands.