Potential carbon release from permafrost soils of Northeastern Siberia

TLDR

Permafrost soils store vast amounts of carbon, and rising temperatures are expected to accelerate thaw‑driven decomposition, but the quantity and lability of deep organic carbon in northeastern Siberia remain poorly quantified. Researchers incubated soils from four continuously frozen tundra and boreal forest sites at 5, 10, and 15 °C to evaluate their potential carbon release upon thaw. Thawing released radiocarbon‑dated CO₂ (≈21–24 ka), with fluxes initially temperature‑dependent (Q₁₀ ≈ 1.9) and later governed by bulk soil carbon, modeling indicated 70 % of respiration derived from dissolved organic C, and extrapolation.

Abstract

Abstract Permafrost soils are an important reservoir of carbon (C) in boreal and arctic ecosystems. Rising global temperature is expected to enhance decomposition of organic matter frozen in permafrost, and may cause positive feedback to warming as CO 2 is released to the atmosphere. Significant amounts of organic matter remain frozen in thick mineral soil (loess) deposits in northeastern Siberia, but the quantity and lability of this deep organic C is poorly known. Soils from four tundra and boreal forest locations in northeastern Siberia that have been continuously frozen since the Pleistocene were incubated at controlled temperatures (5, 10 and 15°C) to determine their potential to release C to the atmosphere when thawed. Across all sites, CO 2 with radiocarbon ( 14 C) ages ranging between∼21 and 24 ka bp was respired when these permafrost soils were thawed. The amount of C released in the first several months was strongly correlated to C concentration in the bulk soil in the different sites, and this correlation remained the same for fluxes up to 1 year later. Fluxes were initially strongly related to temperature with a mean Q 10 value of 1.9±0.3 across all sites, and later were unrelated to temperature but still correlated with bulk soil C concentration. Modeled inversions of Δ 14 CO 2 values in respiration CO 2 and soil C components revealed mean contribution of 70% and 26% from dissolved organic C to respiration CO 2 in case of two permafrost soils, while organic matter fragments dominated respiration (mean 68%) from a surface mineral soil that served as modern reference sample. Our results suggest that if 10% of the total Siberian permafrost C pool was thawed to a temperature of 5°C, about 1 Pg C will be initially released from labile C pools, followed by respiration of∼40 Pg C to the atmosphere over a period of four decades.