Global subsoil organic carbon turnover times dominantly controlled by soil properties rather than climate

Soil organic carbon (SOC) in the subsoil below 0.3m accounts for the majority of total SOC and may be as sensitive to climate change as topsoil SOC. Here we map global SOC turnover times (tau) in the subsoil layer at 1 km resolution using observational databases. Global mean tau is estimated to be 1015(729)(1414) yr (mean with 95% confidence interval), and deserts and tundra show the shortest (146(114)(188) yr) and longest (3854(2651)(5622) yr) tau respectively. Across the globe, mean t ranges from 9 (the 5% quantile) to 6332 years (the 95% quantile). Temperature is the most important factor negatively affecting tau, but the overall effect of climate (including temperature and precipitation) is secondary compared with the overall effect of assessed soil properties (e.g., soil texture and pH). The high-resolution mapping of tau and the quantification of its controls provide a benchmark for diagnosing subsoil SOC dynamics under climate change.