Soils are the largest carbon (C) pool in the terrestrial biosphere, storing about 700 Pg C in the top 0.3 m (Batjes, 1996), or 2,300 Pg C in the top 3 m soil (Jobbágy & Jackson, 2000;Tifafi, Guenet et al. 2018). The amount of carbon below 0.3 m soil is about twice the amount, much older and stable than the carbon in the top 0.3 m soil (Fontaine et al., 2007). A recent soil warming study by Qin et al. (2019) found that the response of soil carbon to warming was dominated by soil microbial activities in the surface soil layer (0-0.3 m), but was codominated by low microbial abundance and strong aggregate protection in the deep (>0.3 m) soil layer. Therefore, deep soil carbon was less sensitive to warming and may function as a carbon sink despite global warming. This is also supported by the analysis of Baldesdent et al. (2018) who found that the soil at the depths between 0.3 and 1 m accounted for about 19% of the total soil carbon accumulated over the last five decades.There has been renewed interest within the global modeling community in representing the vertical variation of soil carbon for several reasons: (1) it enables direct comparisons of the simulations with observations of both soil carbon and carbon isotopes ( 13 C and 14 C) (see Elliott et al., 1996); (2) soil carbon in deeper layers is usually older and more stable than the soil carbon in surface layers (Fontaine et al., 2007;Rossel et al., 2019), and the sensitivity to warming is different between stable soil carbon and active soil carbon (Hicks Pries et al., 2017;Qin et al., 2019); and (3) most Earth system models (ESMs) significantly underestimated soil carbon age by a factor of more than 6, and overestimated the soil carbon sequestration potential by a factor of 2 (He et al., 2016;Shi et al., 2020).