Evaluation of public policy and Covid-19 pandemic impacts on historic Asian pollution emissions using Alaskan ice core lead data

This is the work of Hanna L. Brooks ([email protected]), Michael J. Handley, Karl J. Kreutz, Dominic A. Winski, Jacob Chalif, Erich C. Osterberg, Andrei Kurbatov, Inaglise Kindstedt, Emma Erwin, Scott Braddock, Liam Kirkpatrick, Christopher Gerbi, and Cameron P. Wake.

We acknowledge that Alaska Native peoples have lived on and used the land for thousands of years. Begguya lies at the intersection of the traditional lands of the Ahtna, Dena’ina, Koyukon, Upper Kuskokwim, and Tanana peoples. The Denali Ice Cores were recovered near the summit of Begguya in the Alaska Range, on this ancestral and unceded territory.

This work was completed at the University of Maine. The University of Maine recognizes that it is located on Marsh Island in the homeland of the Penobscot (Panawahpskek) Nation, where issues of water and territorial rights, and encroachment upon sacred sites, are ongoing. Penobscot homeland is connected to the other Wabanaki Tribal Nations — the Passamaquoddy, Maliseet, and Mi’kmaq — through kinship, alliances and diplomacy. The university also recognizes that the Penobscot Nation and the other Wabanaki Tribal Nations are distinct, sovereign, legal and political entities with their own powers of self-governance and self-determination.

Download the Full Resolution poster here:

AGU 2023 Conference Poster

Introduction to the North Pacific Area and the History of Pb Pollution:

Lead (Pb) deposition is typically associated with anthropogenic emissions, and time-series trends can show the influence of human policy, culture, and technology across hundreds to thousands of years. Previous ice core studies have used changes in lead levels through time to examine the effects of industrialization, legislation and worldwide health pandemics. Read more in our new publication:

 Brooks, H. L., Miner, K. R., Kreutz, K., & Winski, D. A., Accepted. A Global Review of Long-range Transported Lead Concentration and Isotopic Ratio Records in Snow and Ice. Environmental Science: Processes & Impacts.

The North Pacific region (Alaska, USA; Kamchatka Peninsula, Russia) is of particular interest when examining historical trends in pollutants (e.g., lead from gasoline, copper from metal smelting) because its position uniquely links the Asian and North American continents. The majority of the ice cores which have been collected in the North Pacific to date have been shallow, encompassing just the last few centuries. At the Begguya site (62.95 °N, 151.09 °W, 3900 m asl) in 2013, two twin cores (DEN-13A and DEN-13B) were drilled to bedrock (210 m), with two shallow cores (DEN-19A and DEN-22A) extending the record. We present a new Pb concentration and isotope record obtained from the DEN-13A, DEN-19A and DEN-22A spanning from 340 to 2022 CE.

Drill site of the Denali Ice Cores, Begguyua (Mt. Hunter), Alaska

Previous Work in the Region

Other cryosphere study sites across the North Pacific Region

Researchers have previously conducted Pb and Pb isotope work at ice core sites across the Northern Hemisphere (Fig. 1, top), with several sites located in the St. Elias Mountains of the North Pacific (Fig. 1, middle) (Gross et al., 2012).

Annual and five-year smoothed data from these sites (Fig. 1, bottom) show a general increasing trend in Pb and Pb isotopes from 1850 to 2002 (Gross et al., 2012).

Figure 1: Pb isotope trends from the North Pacific (Gross et al., 2012)

Figure 2: Pb isotopes can be used to “fingerprint” pollution sources. Here we see atmospheric Pb emissions estimates for countries in Asia for: (A) gasoline, (B) coal-burning, (C) smelting of Cu, Ni, Pb, and Zn ores, (D) totals (*excludes minor sources) and (E) emissions strictly from China (Koffman et al., 2022).

Over time, there has been a progressive shift toward higher 208Pb/207Pb values recorded in the North Pacific over the past 50 years (Figure 3) including (A) 1970s, (B), 1980s, (C), 1990s, and (D) 2000–2001. Data from Eclipse Icefield shown in Fig. 1 is plotted as circles. 2016 Denali snow pit data are squares (Koffman et al., 2022).

Figure 3: Pb isotope data from Eclipse Icefield and Begguya over time (modified from Koffman et al., 2022).

Methodology

Sample of the Denali Ice Core, preparred for Pb analysis. Photo Credit: Erin Towns

For this project, I am using three ice cores to develop a ~1,200 year dataset of natural and anthropogenic variability recorded at Begguya: DEN-13A (210 m) drilled in 2013, a 51 m core drilled in 2019, and a 21 m core drilled in 2022. I melted each ice core using a melting system and ultra-clean sample preparation procedures at Dartmouth College (Osterberg et al., 2006). Combined, the three cores will create a dataset of 1,070 samples spanning 1,700 years of natural and anthropogenic variability in the North Pacific. Ice cores contain very low levels of pollutants, such as lead, making it very difficult to accurately detect their levels within the ice particularly when examining ice older than the Industrial Revolution. Therefore, samples were be analyzed for trace metal concentrations and Pb isotope ratios following established methodologies (Gross et al., 2012) using the UMaine Climate Change Institute (CCI) Inductively Coupled Plasma Mass Spectrometer (ICP-MS) facility located in Sawyer Environmental Research Building. The CCI ICP-MS facility is equiped with a Thermo Element XR with a JET interface system. Using this system, samples can be analyzed directly from ice core meltwater, without the need for column chemistry. We achieved sensitivity of ~70M cps for 1ppb In with a U oxide ratio of 10%.

Hanna getting ready to run my Denali Ice Core samples on the ICP-MS at the University of Maine. Photo Credit: Mike Handley

Preliminary Data

Pb concentration data from the Denali Ice Cores (figures below) shows the same increasing trend seen previously in North Pacific records (Gross et al., 2012; Osterberg et al., 2008). From 5500 BCE (8000 BP) to 1500 CE, the average Pb concentration record is only 5.57 parts per trillion (pg g-1; Osterberg et al., 2008). In 1500, large spikes start to appear in Pb concentration, up to 30 pg g-1 associated with anthropogenic pollution (Fig. 5; Osterberg et al., 2008). However, the large rise in Pb concentration associated with the European and American industrial revolutions (1750s – 1840s), continued rise due to coal mining and tetraethyl lead in gasoline, and fall associated with the banning of leaded gasoline seen in Greenland ice cores are absent here (McConnell et al., 2019). Rather, the record remains relatively unchanged until the 1950s when Pb concentration experiences a large exponential increase from ~20 to ~60 pg g-1 in the 1970s (Gross et al., 2012; Osterberg et al., 2008) to 226.57 pg g-1 in 2001 (Gross et al., 2012). Therefore, these records are recording China’s industrial revolution in 1978 and the subsequent explosion of industrial output from China over the last 45 years (Wen & Fortier, 2019).

Denali Ice Core record of Pb concentration in parts per trillion

Noteably, the increase in Pb concentration is not constant in the Denali Ice Cores, with several marked decreases (i.e., 1990 and 2016).

Denali Ice Core record of Pb concentration in parts per trillion from 1950 to 2022 CE

A new 1,070 sample Pb isotope dataset from 3 ice cores from Denali (Den-13A, Den-19A, and Den-22A) is currently in progress, which will generate a 1,700 year Pb isotope record for the North Pacific when complete. At present, data is avalible for 1970 through 2022.

Examining this dataset, we can see that the progressive shift toward higher 208Pb/207Pb values recorded in the North Pacific over the past 50 years observed by Gross et al (2012) and Koffman et al (2022) is also seen at the Denali Ice Core drill site. Here, we layer the Denali Ice Core data from DEN-19A and DEN-22A over the Pb source bubbles from Koffman et al (2022). Previous North Pacific Pb isotope data only extended to 2001. The 206Pb/207Pb ratio averages 1.176 and 208Pb/207Pb ratios averages 4.45 from 1980 to 2001 at the Eclipse Icefield (Gross et al., 2012), correlating to Chinese aerosol, ore, and coal Pb pollution signatures (Koffman et al., 2022). Examining the 2000s through 2022, we see that the Pb isotope shift continues with Pb isotope values trending further and further away from Alaska silt and USA aerosol signals.

Preliminary Pb isotope data for the Denali Ice Cores

Over the coming months, Pb isotopes will be analyzed on samples from DEN-13A, creating a dataset stretching from 340 till 2022 CE.

Acknowledgements and Funding Sources

Work described here is funded by the National Science Foundation (Grant no. AGS-2002483; AGS-1806422; OPP-2002470), the Graduate Student Government at the University of Maine, and two Graduate Maine Space Grant Consortium Fellowships.

We thank Denali National Park, Polar Field Services and Talkeetna Air Taxi for providing air support and field assistance, Mike Waszkiewicz for ice core drilling, and Brad Markle, Dave Silverstone, Tim Godaire and Elizabeth Burakowski for field assistance. We would like to particularly thank the more than 25 students who have worked on the Denali Ice Core Project for their support in the field and the lab, and to the Ice Drilling Program and Ice Core Facility for their support in retrieval and storage of the Denali Ice Cores.

References:

Gross, Kreutz, Osterberg, McConnell, Handley, Wake, & Yalcin. (2012). Constraining recent lead pollution sources in the North Pacific using ice core stable lead isotopes. Journal of Geophysical Research Atmospheres.

Koffman, B. G., Saylor, P., Zhong, R., Sethares, L., Yoder, M. F., Hanschka, L., Methven, T., Cai, Y., Bolge, L., Longman, J., Goldstein, S. L., & Osterberg, E. C. (2022). Provenance of Anthropogenic Pb and Atmospheric Dust to Northwestern North America. Environmental Science & Technology. https://doi.org/10.1021/acs.est.2c03767

McConnell, J. R., Chellman, N. J., Wilson, A. I., Stohl, A., Arienzo, M. M., Eckhardt, S., Fritzsche, D., Kipfstuhl, S., Opel, T., Place, P. F., & Steffensen, J. P. (2019). Pervasive Arctic lead pollution suggests substantial growth in medieval silver production modulated by plague, climate, and conflict. 6. https://doi.org/10.1073/pnas.1904515116

Osterberg, Handley, Sneed, Mayewski, & Kreutz. (2006). Continuous ice core melter system with discrete sampling for major ion, trace element, and stable isotope analyses. Environmental Science & Technology, 40(10), 3355–3361.

Osterberg, E. C., Mayewski, P., Kreutz, K., Fisher, D., Handley, M., Sneed, S., Zdanowicz, C., Zheng, J., Demuth, M., Waskiewicz, M., & Bourgeois, J. (2008). Ice core record of rising lead pollution in the North Pacific atmosphere. Geophysical Research Letters, 35, L05810. https://doi.org/10.1029/2007GL032680

Wen, Y., & Fortier, G. E. (2019). The visible hand: The role of government in China’s long-awaited industrial revolution. Journal of Chinese Economic and Business Studies, 17(1), 9–45. https://doi.org/10.1080/14765284.2019.1582224