Fix: cryoturbation/bioturbation debug: previously, total SOC was not conserved before and after the diffusion, and an arbitrary adjustment was applied to conserve total carbon. Now the bug is corrected, and no adjustment is needed.
Fix: to improve the SOC vertical profile, an option of depth-controlled SOC turnover time is added, following Koven et al. 2013, Biogeosciences, Equation (7). A flag "depth_modifier" is added, with the default value giving the same result as before this modification.
Fix: to increase (improve) the total SOC stock, the calculation of "shumdiag_perma", which is used to calculate the "moisture modifier" in soil carbon decomposition rate in MICT, is modified to use the absolute soil moisture, instead of the relative value (divided by moisture at saturation).
Done by Dan
