Pedogenic carbonate as a transient soil component in a humid, temperate forest (Michigan, USA)
Julia R. Kelson, Tyler E. Huth, Kirsten Andrews, Miriam Bartleson, Thure E. Cerling, Lixin Jin, Matthew Salinas, Naomi E. Levin
Abstract
Abstract In humid, continental Michigan, we identified pedogenic carbonate in a soil profile developed on glacial drift sediments, as rinds, rhizoliths, and filaments (at depths >50 cm). Given that the climate setting is unusual for pedogenic carbonate, we investigated its formation with environmental monitoring and isotope analyses of carbonate (δ 13 C, δ 18 O, Δ 47 , and 14 C) and waters (δ 18 O and δ 2 H). We found covariation in δ 13 C and Δ 47 amongst the carbonate types (rhizoliths, rinds, filaments, bulk soil, and detrital clasts), and 14 C ages of rinds that predate plausible formation ages. The δ 13 C and Δ 47 values of the bulk carbonate and some of the pedogenic morphologies are not fully compatible with pedogenic formation in the modern environment. The δ 18 O data from precipitation and river waters and from carbonates are not uniquely identifying; they are compatible with the soil carbonate being pedogenic, detrital, or a mix. We conclude that the soil carbonate is likely a physical mix of pedogenic and detrital carbonate. Pedogenic carbonate is forming in this humid setting, likely because seasonal cycles in soil respiration and temperature cause cycles of dissolution and re-precipitation of detrital and pedogenic carbonate. The pedogenic carbonate may be a transient feature as carbonate-rich till undergoes post-glacial chemical weathering.