Translating bumblebee dialect…
Soil organic carbon (OC) constitutes the largest terrestrial pool of carbon, and changes in its size have the potential to modulate atmospheric CO2 levels. As such, the underlying controls on OC stabilization and their sensitivities to climatic change have been increasingly scrutinized. The existing paradigm for OC stabilization suggests that due to their high specific surface areas and negatively charged surfaces, secondary clay minerals that form in soil protect OC from oxidation. Thus, a direct relationship between clay mineral abundance and OC may hold across soil types and climates. Despite this understanding, reactive transport models (RTMs) cannot reconcile soil geochemistry and OC profiles, pointing to knowledge gaps regarding organo-mineral interactions and their constitutive controls. Consequently, these challenges result in great uncertainty in the treatment of soil OC dynamics in Earth systems models and their concomitant effects on future climate projections. To further understand clay mineral formation and its relationship with OC dynamics over a hydrologic year, Here we propose to advance our understanding of clay mineral formation, OC stabilization, and their controls across a recently deglaciated, headwater catchment (East River watershed) using high-frequency geochemical analyses that track clay mineral formation. Preliminary analyses, including a numerical inversion of a solute time series show that the amount of cation uptake by clay varies on short (event) timescales. These same events also feature changes in dissolved carbon species, which may be plausibly linked to the dynamics of clay mineral cycling. Following these results, we designed preliminary RTMs that include Li isotopes: a novel proxy for clay formation. The models predict a covariation in Li isotope ratios (in sediment and soil water) with solid-phase and dissolved OC. Together, these results support clay mineral formation as a dynamic and seasonally modulated process that is closely linked to OC dynamics. Planned measurements of Li isotope ratios of soil, river water, and bedrock in the East River, along with new RTMs with variable organo-mineral couplings, will help validate these preliminary findings.