From time capsule to carbon source: Paleosol exposure as a missingcomponent in soil-climate feedbacks

Buried soils (paleosols) represent vast but under-characterized reservoirs of long-term soil organic carbon (SOC) that can persist for millennia when isolated from surface processes (Marin-Spiotta et al., 2014; Berhe et al., 2018). Their stability depends on geomorphic protection and mineral–organic interactions that constrain microbial decomposition (Kleber et al., 2007; Kögel-Knabner et al., 2022), but this protection may be compromised when erosion, hydrologic variability, or land-use change reconnect buried carbon to the atmosphere (Doetterl et al., 2016; Berhe et al., 2012).

Using the late Pleistocene Brady paleosol in Nebraska (USA) as a model system, we combined geochemical, isotopic, and incubation approaches to examine mechanisms controlling SOC persistence and reactivation across burial and erosional settings. Radiocarbon and spectroscopic data show that millennia-old SOC is stabilized by fine-textured minerals and polyvalent cation bridging (Ca²⁺, Mg²⁺), which promote aggregation and organo-mineral bonding. Burial enhanced these stabilization mechanisms, whereas erosional exposure induced geochemical convergence toward modern surface soils and faster SOC turnover.

Incubation experiments further revealed that drying–rewetting cycles accelerate decomposition and destabilize even the slow-cycling pool, while continuously moist, deeply buried horizons retained low decomposition rates and greater mineral-associated carbon fractions. These results demonstrate that SOC persistence is jointly controlled by geomorphic position, ionic environment, and moisture regime, linking ancient pedogenesis with modern disturbance.

Because loess–paleosol sequences also occur throughout Central and Eastern Europe, these findings provide a valuable framework for assessing the vulnerability of deep-soil carbon pools to future climate and land-use change. Integrating paleosol processes into soil–climate models will improve predictions of carbon feedbacks and inform management of legacy carbon reservoirs.