[Reading Science] How Do the Polar Regions Remember Nuclear Tests?

KOPRI Reveals Seasonal Patterns of Atmospheric Transport
Using Plutonium-239 Traces in Arctic and Antarctic Ice

Traces of atmospheric nuclear tests conducted in the Pacific during the 1950s have been preserved in the ice of both Antarctica and the Arctic. A Korean research team used these radioactive substances as clues to identify the 'seasonal pathways' of global atmospheric transport, which moves from the stratosphere through the troposphere to the polar regions.

On October 27, the Korea Polar Research Institute announced that it had successfully reconstructed the temporal and spatial patterns of air movement by analyzing minute traces of plutonium-239 (Pu-239) left in Antarctic and Greenland ice. This achievement marks the first time that the spread of nuclear test fallout through Earth's atmosphere has been confirmed using direct observational data.

Researchers posed with the ice cores they drilled at the 2013-14 Antarctic Styx Glacier drilling site. Photo by Korea Polar Research Institute

Antarctica Remembers the Traces of Nuclear Tests

The research began by tracking how fallout from atmospheric nuclear tests between 1950 and 1980 spread globally.

Dr. Han Youngcheol's team analyzed ice cores collected from four locations, including Antarctica and Greenland, and precisely measured the amount of plutonium-239 accumulated in the ice over several decades.

As a result, they were able to clearly distinguish the traces of the 'Ivy Mike' test in 1952 and the 'Castle' test in 1954. Although both tests were conducted on neighboring atolls in the Marshall Islands in the Pacific, the traces of 'Castle' were distinctly found in Antarctic ice, while the traces of 'Ivy Mike' were weak or recorded much later.

Seasonal Differences Left by the Atmosphere

The research team attributed these differences to 'seasonal changes in atmospheric circulation.'

This is because the process by which fine radioactive particles generated during nuclear tests rose into the stratosphere and then descended into the troposphere or moved toward the poles varied depending on the season.

A graph showing the temporal correlation between plutonium-239 fallout recorded in Arctic and Antarctic ice cores and the scale of nuclear tests. This graph compares the timing of nuclear tests from 1945 to 1980 with changes in plutonium-239 concentration in ice cores from the Arctic (Greenland NEEM) and Antarctic regions. Large-scale nuclear tests were mainly conducted in the Northern Hemisphere, and the peaks in plutonium concentration in each core correspond to major nuclear test periods. Provided by the Korea Polar Research Institute

In particular, during the Southern Hemisphere summer, air exchange between the stratosphere and troposphere becomes more active, making it more likely that substances at higher altitudes are transported rapidly to the polar regions.

This study is the first to provide direct observational evidence that such exchange phenomena actually vary by season, offering scientific support for theoretical hypotheses in existing atmospheric models.

Earth's Memory Preserved in Ice

The amount of plutonium-239 analyzed by the research team was at an extremely minute level of about 10?¹? grams per gram of ice. This level of precision can only be measured using some of the world's most advanced analytical techniques, and in this study, the researchers were able to distinguish not only annual but also seasonal fluctuations.

The results confirmed that the glaciers of the Arctic and Antarctic serve as 'natural time capsules,' recording the traces of humanity's nuclear tests.

This data is expected to be used not only to improve the accuracy of atmospheric transport models in the future, but also to be applied in predicting volcanic ash dispersion, analyzing climate change, and simulating geoengineering material injections.

Antarctic Hercules Nv Glacier Drilling Site and Glacier Core. Provided by Korea Polar Research Institute

Shin Jinhwa, the first author of the paper, stated, "The fallout from past nuclear tests has been repurposed for today's atmospheric science research," adding, "This study presents a new method for tracing the 'invisible pathways' of Earth's atmosphere."

Shin Hyungcheol, Director of the Korea Polar Research Institute, commented, "From securing Antarctic samples to analysis, interpretation, and modeling, this achievement was independently carried out by Korean researchers. It is a testament to Korea's glacial analysis technology and research capabilities on the global stage."

The results of this study were published in the October issue of the international journal Science Advances. The paper is titled "Tracing Stratosphere-Troposphere Exchange Using Fallout Plutonium Signatures in Polar Ice Cores," with Shin Jinhwa as the first author and Han Youngcheol as the corresponding author.