ATMOSPHERIC DEPOSITION OF FALLOUT RADIONUCLIDES (FRNS) 7BE AND 210PB: PATTERNS, PROCESSES AND POST-DEPOSITIONAL FATES

The fallout radionuclide (FRNs) ⁷Be and ²¹⁰Pb have seen over 5 decades of study as tracers in both atmospheric and terrestrial research. However, the interaction between atmosphere and biogeosphere during deposition of FRNs, which determines their partitioning to terrestrial surfaces and materials, is not well understood. Towards “closing” this gap in FRN biogeochemical cycling, we compiled a long-term, high-resolution record of FRN deposition. This record includes 9 years of weekly bulk openfall at our mid-latitude, continental location (44°N, 72°W; Dartmouth College, Hanover, NH, USA). We include 3 years of speciated openfall (by filtration at 0.5 µm), event-based throughfall and sampling of tree leaves, and air filtration of ambient aerosols. Through analysis of these records, we attribute FRN behavior to a combination of physical processes (source effects and depositional mechanisms), elemental chemical effects (pH and aqueous chemistry), meteorological and seasonal influences, and a ‘particle-age effect’ related to differing half-lives of the FRNs. We conclude that ⁷Be:²¹⁰Pb ratios observed in terrestrial materials can reflect honest chronometry, but source effects and divergent chemistries of ⁷Be and ²¹⁰Pb during deposition must be considered . An improved understanding of FRN biogeochemical cycles can augment the power of FRN tracers in geomorphic and fluvial research, refine their use as chronometers, and foster their application to contaminant dispersal and the global crisis in particulate matter (PM) air quality.