2 Environmental Radionuclides: Geochemical Behavior, Tracer Applications, and Potential Health Consequences

Friday, 17 March 2023
8:00 AM - 12:00 PM
Regency Ballroom A

CONCORDANT CHRONOMETERS OF MODERN SOIL PROCESSES: ALIGNING 7BE:210PB, 228TH:228RA, 241AM BOMB-PULSE METHODS

Paper number: 2-10
Program: Symposia
Time: 10:40 AM – 11:00 AM

Authors

Abstract

Anthropogenic forcing is changing soil-vegetation systems with a range of implications, for example altering rates of carbon mineralization and accumulation of contaminants such as mercury (Hg). Understanding modern change in soil biogeochemical processes requires age models that are accurate and precise over annual-decadal timescales. Here I describe efforts to establish concordant chronometers of modern soil processes using a suite of short-lived radionuclides that includes 7Be, 210Pb, 241Am, 228Th and 228Ra. The Linked Radionuclide aCcumulation (LRC) chronometer, based on atmospheric deposition of 7Be and 210Pb to vegetation and soil (the 7Be:210Pb ratio), accurately predicts the depth of the 1963-4 bomb-pulse peak of 241Am (plutonium daughter) in diverse soils, peat and saltmarsh, with corresponding calendar year of 1964.1 (age = 58 ±3 years, mean ±1SD, n=14 soil profiles). At shorter timescales, the 228Th:228Ra chronometer, which is based on assimilation of 228Ra by vegetation and in vivo ingrowth of daughter 228Th in foliage, litter and humus, might provide a key corroborator of LRC in the 0-5 year window, that includes soil Oi and Oe horizons. Preliminary results show good agreement between LRC and 228Th:228Ra methods, differing by 0.10 ±1.2 years (mean ±1 SD; n=26 soil horizons). Concordance of these three independent radionuclide chronometers thus suggests that the LRC model can provide insights into metal-carbon pedogenic processes at the patch scale over subannual to centennial timescales.

Geological Society of America Abstracts with Programs. Vol. 55, No. 2

doi: 10.1130/abs/2023SE-385647

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