Soil organic carbon stocks at depth are poorly known despite their central importance to the global carbon cycle. Florez Orosco and others demonstrate a novel method for estimating these carbon stocks using complex electrical conductivity. Increases in low frequency polarization are linearly related to soil organic carbon, which was used to discover soil organic carbon at 4-6 m depth in a catchment dominated by silty loam soils. Their findings present a path forward for quantifying deep soil organic carbon stocks across different terrestrial ecosystems.