Size, distribution and vulnerability of the global soil inorganic carbon

Global estimates of the size, distribution, and vulnerability of soil inorganic carbon (SIC) remain largely unquantified. By compiling 223,593 field-based measurements and developing machine-learning models, we report that global soils store 2305 ± 636 (±1 sigma) Gt of carbon as SIC over the top 2m depth. Under future scenarios, soil acidification associated with nitrogen additions to terrestrial ecosystems will reduce global SIC (0.3m) up to 23 GtC over the next thirty years, with India and China being the most affected. Our synthesis of present-day land-water carbon inventories and inland-water carbonate chemistry reveals that at least 1.13 ± 0.33 GtC of inorganic carbon is lost to inland-waters via soils annually, resulting in large but overlooked impacts on atmospheric and hydrospheric carbon dynamics.