Estimation of Permafrost SOC Stock and Turnover Time Using a Land Surface Model With Vertical Heterogeneity of Permafrost Soils. Issue 11 (18th November 2020)

• Record Type: Journal Article
• Authors: Shu, Shijie; Jain, Atul K.; Koven, Charles D.; Mishra, Umakant
• Is Part Of: Global biogeochemical cycles. Volume 34:Issue 11(2020:Nov.)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-11-18
• Subjects: northern high latitudes permafrost -- soil organic carbon stock -- soil turnover time -- cryoturbation -- CO2‐carbon cycle feedback -- climate‐carbon cycle feedback; Biogeochemical cycles -- Periodicals; Electronic journals; 577.1405
• DOI: 10.1029/2020GB006585
• Languages: English
• ISSNs: 0886-6236

Abstract

Abstract: We developed vertically resolved soil biogeochemistry (carbon and nitrogen) module and implemented it into a land surface model, ISAM. The model captures the vertical heterogeneity of the northern high latitudes permafrost soil organic carbon (SOC). We also implemented Δ 14 C to estimate SOC turnover time, a critical determinant of SOC stocks, sequestration potential, and the carbon cycle feedback under changing atmospheric CO2 concentration [CO2 ] and climate. ISAM accounted for the vertical movement of SOC caused by cryoturbation and its linkage to frost heaving process, oxygen availability, organo‐mineral interaction, and depth‐dependent environmental modifiers. After evaluating the model processes using the site and regional level heterotrophic respiration, SOC stocks, and soil Δ 14 C profiles, the vertically resolved soil biogeochemistry version of the model (ISAM‐1D) estimated permafrost SOC turnover time of 1, 443 years, which is about 3 times more than the estimation based on the without vertically resolved version of ISAM (ISAM‐0D). ISAM‐1D‐simulated SOC stocks for permafrost regions was 319 Pg C in the top 1 m soil depth by the 2000s, about 80% higher than the estimates based on ISAM‐0D. ISAM‐1D SOC stock and turnover time were compared well with the observations. However, the longer SOC turnover time preserves less SOC stocks due to the lower carbon use efficiency (CUE) for SOC than ISAM‐0D and thus respires more SOC than being transferred downward by cryoturbation. ISAM‐1D simulated reduced SOC sequestration (3.7 Pg C) compared to ISAM‐0D (4.8 Pg C) and published Earth system models (ESMs) over the 1860s–2000s, due to weaker [CO2 ]‐carbon cycle and stronger climate‐carbon cycle feedbacks, highlighting the importance of the vertically heterogeneous soil for understanding the permafrost SOC sinks. Key Points: Vertically resolved SOC cryoturbation process is implemented in ISAM for capturing the observed permafrost SOC stock and turnover time ISAM‐1D Calibrated carbon use efficiency for SOC pools shows increased respiration and less SOC transported downward through cryoturbation ISAM‐1D estimates reduced SOC sequestration due to weaker CO2 fertilization effect and stronger climate‐carbon cycle feedback during the 2000s