Dominant control of temperature on (sub-)tropical soil carbon turnover

Carbon storage in soils is important in regulating atmospheric carbon dioxide (CO2). However, the sensitivity of the soil-carbon turnover time (τsoil) to temperature and hydrology forcing is still not fully understood. Here, we use radiocarbon dating of plant-derived lipids in conjunction with reconstructions of temperature and rainfall from an eastern Mediterranean sediment core receiving terrigenous material from the Nile-River watershed to investigate τsoil in subtropical and tropical areas during the last 18,000 years. We find that the τsoil was reduced by an order of magnitude over the last deglaciation and infer that this reduction was caused from amplified soil respiration rates. Our data indicate that the deglacial warming was the major driver of these changes while the impact of hydroclimate was relatively small. We conclude that increased CO2 efflux from soils into the atmosphere constituted a positive feedback to global warming. However, simulated glacial-to-interglacial changes in a dynamic global vegetation model underestimate our data-based reconstructions of soil-carbon turnover times suggesting that this climate feedback might be underestimated.