In the Cox Bay soil chronosequence, we show that the production of acidity (protons and complexing organic acids) in temperate forests and the subsequent Podzol formation imply heavy 30Si enrichment in pedogenic clay minerals of E horizons relative to the “unweathered” clay minerals in BC horizon; Δ30SiE–BC increasing from +1.01 to +2.04‰ in ca. 200 years (Table 2).