Abstract

We couple meteoric ¹⁰Be measurements with mass balance analysis of ⁹Be to estimate the
soil residence time (SRT) of a biogeomorphically stable Ultisol in the Southern Piedmont
physiographic region of the southeastern United States. We estimate SRT after correcting the
meteoric ¹⁰Be inventory to account for observed ⁹Be losses, which indicate that more than half
of the ⁹Be weathered from primary minerals has been leached from the upper 18.3 m of the
Ultisol. Our estimates of minimum SRT range between 1.3–1.4 Ma and between 2.6–3.1 Ma
under high and low (2.0 and 1.3 × 106 atoms cm^–2 yr^–1, respectively), estimates of 10Be delivery.
Denudation rates of the physiographic region corroborate our estimates. We redefi ne pedogenic
time constraints in the Southern Piedmont, and demonstrate that the assumption of
complete meteoric ¹⁰Be retention in acidic soil systems cannot always be made; the latter has
far-reaching consequences for soil, sediment, river, and ocean research using meteoric ¹⁰Be.

Citation

Bacon, Allan R., Daniel deB. Richter, Paul R. Bierman, and Dylan H. Rood (2012): Coupling meteoric ¹⁰Be with pedogenic losses of ⁹Be to improve soil residence time estimates on an ancient North American interfluve. Geology 40 (9): 847–850. DOI: 10.1130/G33449.1