Radioactive particles in Pacific sediments could usher in a new era

(ORDO NEWS) — The Anthropocene is the name some scientists give to the current geological epoch, denoting the point in time when human activity began to have a significant impact on the Earth‘s geology and ecosystems – not least through climate change.

Scientists now believe they have pinpointed the beginning of the Anthropocene from specific biomarkers – radioactive materials found in marine sediments and corals in the Pacific Northwest, off the coast of Japan.

This material was obtained from atomic tests carried out in this region in the 1950s and represents a clear change in the ocean environment.

Based on the data collected, the research team suggests that the Anthropocene epoch began in 1954.

“Our task was to find clear signs of radioactive fallout from the 1950s until 1963, when testing basically ceased. We took core samples from the bay area, and there are clear signals of plutonium from radioactive fallout,” – says geophysicist Yusuke Yokoyama of the University of Tokyo in Japan.

“However, we also collected coral skeletons from Ishigaki Island, southwest of Okinawa, that contained sediment. Comparing the sediment with coral allows us to more accurately date the signatures we see in the sediment.”

The collection and comparison of these samples is complicated by the fact that sediments can be dispersed over a large area and easily moved by ocean currents and other factors. This means that cross-matching sediments with corals that are anchored in place is critical.

Like trees, corals have specific rings that correspond to specific growth years. Although they do not give scientists as much information about the state of the water, they are a good addition to the sedimentary material in terms of dating.

A variety of chemical analysis techniques have been used to study in detail sections of sampled sediments, including accelerator mass spectrometry, or AMS, which uses accelerated ions to determine individual isotopes in sediments.

“Analyzing the plutonium in our samples was not an easy task, because three tons of plutonium were released into the sea and atmosphere during the period under review, but these three tons were dispersed far and wide. Therefore, we are looking for incredibly small signatures,” says Yokoyama.

Officially, the geologic epoch we’re in now is called the Holocene – it started about 11,700 years ago, and scientists from many fields believe it’s necessary to recognize the significant shifts we’ve seen in recent decades, largely man-made.

At present, no one can decide when exactly the Anthropocene should start: perhaps with the industrial revolution or with the start of an increase in carbon dioxide emissions. But for the scientists behind this new study, there is a clear point where it starts.

“This work is important not only to refine the definition of the Anthropocene, but also because the success of our method means it can be used to improve ocean and climate models, or even to study tsunamis and other geological hazards in the past,” says Yokoyama.

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