GSA 2020 Connects Online

Paper No. 167-2
Presentation Time: 5:50 PM


WENSMAN, Sophia M.1, SHIEL, Alyssa E.1 and MCCONNELL, Joseph R.2, (1)College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, 104 CEOAS Administration Bldg., 101 SW 26th St, Corvallis, OR 97331, (2)Division of Hydrologic Sciences, Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512

The pervasiveness of lead (Pb) pollution is evidenced by elevated Pb levels found even in the least disturbed regions of the Arctic and Antarctic. Beyond most recent history, Pb pollution can be observed in ice core records spanning the last three millennia. Pb concentration records in ice cores have been successfully linked to social and political changes including periods of economic expansion, wars, and plagues[1]. Determination of the origin of Pb in such samples can only be derived from their Pb isotopic composition. Recent advancements in low-level measurement capabilities using high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS), provide means for obtaining more precise, high resolution records than previously possible[2].

An approximately annual record of Pb isotopes was resolved using a Greenland ice core spanning the last 250 years (1759-2009). Lead isotopic ratios from the earliest samples (1759–1817) suggest the dominance of a coal derived signal, stemming from the expansion of coal extraction and use in Britain and Ireland. Variation observed in the Pb isotope record between 1860–1930 corresponds to the expansion of coal use in the rest of Europe, as well as Asia and North America. With the introduction of leaded gasoline around the 1930s there is a shift towards higher 206Pb/207Pb levels attributed to an increase in leaded gasoline use in the US. During the phase out of leaded gasoline in the US (1975-1995), this isotopic ratio shifts towards lower 206Pb/207Pb ratios, indicating a decline in US leaded gasoline use, and a shift towards predominantly Eurasian leaded gasoline sources.

To our knowledge, this study represents the highest resolution record of Pb isotopes in ice cores available to date. Examination of temporal changes in Pb source provides a means of better understanding the legacy of anthropogenic Pb pollution in what are often considered pristine environments.

[1]McConnell, J.R., et al. (2018), Proc. Natl. Acad Sci, 115(22), 5726-5731.

[2]Smith, K.E., et al. (2019), Nat. Sustain., 2(3), 223-232.