Mysterious radiation anomaly found deep in the Pacific Ocean
A strange radiation anomaly has been found deep in the Pacific Ocean. By analyzing several thin layers of seafloor crust, German scientists have found a sudden increase in the radioactive isotope beryllium-10 sometime between 9 million and 12 million years ago.
The beryllium-10 anomaly has been observed on the seafloor of the central and northern Pacific Ocean, but the study’s author, physicist Dominik Kohl of the Helmholtz Zentrum Dresden-Rossendorf, says it could be present throughout the Pacific Ocean and even around the world.
It’s not clear where this sudden increase came from, but researchers have some ideas.
Beryllium-10 is a radioactive isotope that is constantly produced by cosmic rays interacting with Earth’s atmosphere. When the isotope rains down from the atmosphere into the ocean, it becomes incorporated into the very slow growth of some deep, mineral-rich crust.
Cole and his colleagues believe that more than 9 million years ago, there was a “major reorganization” of ocean currents that led to more Be-10 being deposited in the Pacific.
This may have been a global phenomenon. The authors also think that cosmic rain from supernovae near Earth or our solar system passing through cold interstellar clouds could have led to increased cosmic ray activity, leading to increased Be-10 deposits in the oceans.
Ferromanganese crusts containing Be-10 are found in all of Earth’s oceans and can record millions of years of ocean chemistry in just a few millimeters.
Researchers can use the slow rate at which Be-10 radioactively decays into boron as a time measurement and compare the ratios of the two chemicals to determine the age of minerals in the crust.
These thin, ancient crusts form a nearly continuous geological timeline of Earth’s past 75 million years, but they are difficult to date. Carbon dating only goes back about 50,000 years, and measurements based on the decay of uranium isotopes are not useful indicators either.
Beryllium-10 was key to finding that the crust capsule was at least 10 million years old.
Beryllium-10 has a half-life of about 1.4 million years, which means it is often used to date ferromanganese crusts up to 20 millimeters thick. Most ferromanganese crusts are 1 to 26 centimeters thick.
But what Cole and his team found in the Pacific Ocean was surprising.
“We found twice as much 10Be as we would have expected when the element is about 10 million years old,” explains Cole. “We found an anomaly that had never been seen before.”
“These anomalies have the potential to be independent time markers in the ocean archive,” the team says.
The team has verified their work in several areas of the Pacific Ocean. A 50-million-thick ferromanganese crust could date back more than 18 million years.
The growth rate of Pacific ferromanganese crusts was determined to be about 1.52 millimeters per million years, which means that the depth of the anomaly dates back to between 10.5 and 11.8 million years.
Wherever the beryllium-10 anomaly appears in these samples, it is essentially associated with this age.
“The origin of this anomaly remains unknown,” the authors say, but since our solar activity may not have been high enough to cause such a persistent increase in beryllium, the team suspects that Earth’s protection from interstellar cosmic rays may have changed about 10 million years ago.
Or perhaps a nearby supernova blasted more radioactive material toward our planet than usual.
“Only with further measurements will we be able to determine whether the beryllium anomaly is due to changes in ocean currents or has an astrophysical cause,” Cole said.
“We therefore plan to analyze more samples in the future and hope that other research groups will do the same.”
Only time will tell whether the beryllium anomaly is a regional or global phenomenon.
