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During the last deglaciation, atmospheric CO2 increased by about 75 ppm. The deep ocean is likely the dominant source of this atmospheric CO2 rise in the atmospheric pool; however, a consensus accounting for the entire 75 ppm remains elusive. Since the deep ocean cannot account for the entire 75 ppm, the terrestrial environment likely makes up the remainder. This paper provides a mechanism for an unaccounted-for portion of the source of this terrestrial carbon, that being soil organic carbon (SOC) from the tropical montane Andes, and with that, minimum constraints on the contribution of SOC to the total rise in atmospheric CO2 during the last deglaciation. Using numerical climate modeling input into an empirical model derived from tropical montane forests of the Andes Mountains in South America, this study finds that during the last deglaciation, the organic layer thickness was thinning from the Last Glacial Maximum (LGM) to the present (pre-industrial) in the tropical montane Andes. This overall warming and organic layer thickness thinning may have led to a loss of available carbon storage space, causing a leak of CO2 into the atmosphere over this time scale. This study finds an estimate for the contribution of global atmospheric CO2 from SOC in tropical montane Andean soils is likely at least ∼1.4 ppm CO2 since the LGM. [ABSTRACT FROM AUTHOR]