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 the Denali Ice Cores were recovered near the summit of Begguya in the Alaska range which lies within the traditional homelands of groups that have occupied the region for thousands of years prior to our study. Additionally, data was collected at the University of Maine in the homeland of the Penobscot Nation.

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Introduction to the North Pacific Area:

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. 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.

Drill Site

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.

Previous Work in the 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).


Gross et al., 2012 Pb isotope trends from the North Pacific:

Gross 2012

Pb isotopes can be used to “fingerprint” pollution sources. Figure 2 shows 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).



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%.

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).

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

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.

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. Collection of the ice core was assisted by the U.S. Ice Drilling Program, the National Park Service and Talkeetna Air Taxi. The National Science Foundation – Ice Core Facility assisted with ice core sampling and curation.


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