Radioactive Traces in Ocean Materials Mark the Beginning of the Modern Age

Defining the Anthropocene: Radioactive Traces in Ocean Materials Mark the Beginning of the Modern Age

Coral rings. A cross section of coral reveals growth rings. These correspond to different years, so researchers can look for markers to see when certain atmospheric changes occurred. Credit: Yokoyama et al.

For the first time, researchers can provide a strong quantitative definition of the genesis of what is known as the Anthropocene, thanks to traces of radioactive material in marine sediments and corals. The Anthropocene Period is considered important by researchers in many fields, as it basically marks a milestone in humanity’s impact on the Earth’s environment and ecosystem.

Researchers combined records of nuclear fallout from atomic tests present in ocean sediments and coral skeletons. These data show a marked change in the ocean environment before, during and after a period of global nuclear testing, which the researchers defined as the beginning of the Anthropocene.

There are many reasons to visit the seaside town of Beppu in southwestern Japan, famous for its historic hot springs, beautiful beaches and lively traditional festivals. However, on a recent trip there, Professor Yusuke Yokoyama of the Atmosphere and Ocean Research Institute at the University of Tokyo, Michinobu Kuwae, an associate professor at Ehime University and leader of the Beppu Bay project, and their colleagues visited so as not to enjoy themselves. of the local atmosphere, but to explore some interesting properties of the local seabed. It may not sound like everyone’s favorite beach activity, but they were looking for evidence of plutonium from atomic bomb tests in the Pacific over 50 years ago, and other chemical imprints left behind by mankind.

“Beppu Bay is one of several areas around the Pacific Ocean that contain well-preserved data on humankind’s impact on the environment due to sediments forming layers on the Pacific seafloor. For example, plutonium waste from nuclear tests has been preserved in the mid-20th century,” Yokoyama said.

“Our job was to find clear evidence of fallout from the 1950s to 1963, when testing largely ceased. We took core samples from the bay area, and there are clear signs of the plutonium of fallouts. However, we also collected coral skeletons from Ishigaki Island, southwest of Okinawa, that contained precipitation. By comparing sediments to corals, we can more accurately date the signatures we see in the sediments.”

Defining the Anthropocene: Radioactive Traces in Ocean Materials Mark the Beginning of the Modern Age

Beppu Bay. An aerial view of Beppu Bay, where the sediment samples were collected. Credit: Yokoyama et al.

Even settle samples can capture evidence of past environmental changes, so they are deposited haphazardly and can be easily disrupted. This is why the team had to make a cross reference to the core samples with coral, like coral, like trees, grow in such a way that their internal structure leaves several rings corresponding to each growing year. The reason both types of records are useful is that sediments tend to capture a wide range of environmental information, but are not accurate, and coral, thanks to their growth rings, can provide great historical precision, but not as much information about past times. records environmental information. Modify. As a result, the team found clear evidence in coral skeletons from fallout from 1954; other markers in that coral that were also found in the sediments meant that the broader range of chemical signatures in the sediments could be linked to that same year.

The reason why Yokoyama and colleagues are eager to find geological and chemical data on nuclear material? precipitation is that they are part of an initiative to redefine how we refer to the modern age. Our period in history is commonly known as the Holocene, which dates back about 12,000 years. However, humanity’s unprecedented impact on the Earth since the dawn of the industrial age has proved so monumental that researchers in many fields related to history, biology, atmospheric science and more, trying to create a new accurate definition for this modern post-nuclear age, which they call the Anthropocene.

Defining the Anthropocene: Radioactive Traces in Ocean Materials Mark the Beginning of the Modern Age

In the lab. The equipment needed to accurately date sediment and coral samples using tiny amounts of embedded plutonium from fallout created during nuclear tests in the 20th century. Credit: Yokoyama et al.

“It was a challenge to analyze plutonium in our samples because during the period in question three tons of plutonium were released into the sea and the atmosphere, but those three tons spread far and wide. So we’re actually looking for incredibly small autographs,” Yokoyama said.

Nevertheless, this work is important not only in solidifying the definition of the Anthropocene, but also because the successful use of our method means it can also be used to improve ocean and climate models, or even to analyze past tsunamis and other geological hazards. to investigate. “

The research was published in Scientific Reports

Environmental scientists approach ‘golden peak’ to define the Anthropocene

More information:
Yusuke Yokoyama et al, Plutonium isotopes in the Northwest Pacific sediments combined with radiocarbon in corals recording the precise timing of the Anthropocene, Scientific Reports (2022). DOI: 10.1038/s41598-022-14179-w

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