Posted by Design Studio
16 December 2025
Challenge 2: Soil Carbon
Introduction
Field measurements, after extrapolation, suggest that deep Yedoma deposits (ice-rich, organic-rich permafrost, formed during the late Pleistocene) and peatlands (formed mostly during the Holocene) account for about 600 Pg C of soil carbon storage. Incorporating this old, deep, cold carbon into land surface models (LSMs) is crucial for accurately quantifying soil carbon responses to future warming. However, it remains underrepresented or absent in current LSMs, which typically include a passive soil carbon pool (a conceptual soil carbon pool with the longest turnover time) to represent all “old carbon” and lack the vertical accumulation processes that deposited deep carbon in the layers of peatlands and Yedoma deposits. This article propose a new, more realistic protocol for simulating deep and cold carbon accumulation in the northern high latitudes (30–90° N), using the ORCHIDEE-MICT land surface model.
Representation of deep carbon in ORCHIDEE-MICT
To represent deep carbon, we implemented two main developments. First, we integrated deep carbon associated with Yedoma deposits, whose formation is simulated under Last Glacial Maximum climate conditions. Second, we prescribed the timing and spatial distribution of northern peatland initiation during the Holocene using spatially explicit data on peat age.
Impacts of deep carbon representation on the pre-industrial soil organic carbon state
Our results show an additional 157 Pg C in present-day Yedoma deposits, as well as a shallower peat carbon depth (by 1–5 m) and a smaller passive soil carbon pool (reduced by 35 Pg C, 43 %) in northern peatlands, compared to the old protocol that ignored Yedoma deposits and applied a uniform, long-duration (13 500 years) peat carbon accumulation across all peatlands. As a result, the total organic carbon stock across the Northern Hemisphere (30–90° N) simulated by the new protocol is 2028 Pg C, which is 226 Pg C higher than the previous estimate.
Outlook
Although simulating deep carbon remains challenging in ORCHIDEE-MICT, the improvements in the representation of carbon accumulation in our study provide a model version to predict deep carbon evolution during the last glacial–deglacial transition and its response to future warming. The methodology implemented for deep carbon initialization in permafrost and cold regions in ORCHIDEE-MICT is readily transferable to other LSMs.
Schematic representation of soil carbon accumulation within one grid cell across different simulation stages in the old and new spin-up simulations
