(CNN)Decades after the nuclear bomb tests of the Cold War, traces of radioactive carbon have been found in the deepest parts of the ocean.
Radioactive carbon from Cold War nuclear tests has been found deep in the ocean
Crustaceans found in the deepest trenches of the Pacific Ocean showed high levels of radioactive carbon in their muscle tissues, according to a study published in the journal Geophysical Research Letters in April.
The "bomb carbon" found its way into their molecules from nuclear tests performed in the 1950s and '60s -- and it's been found miles down into the ocean where these creatures live. The results show how quickly human pollution can enter the ocean's food chain and reach the deep ocean, according to the study's authors.
It's a disturbing discovery that shows how the actions of humans can harm the planet.
"We didn't expect such high levels of carbon-14 (radioactive carbon)," co-author Weidong Sun, a professor of marine geology at the Chinese Academy of Sciences in Qingdao, China, told CNN. "That means the ocean has been polluted by human activities."
During the nuclear tests of the Cold War era, the radioactive carbon in the atmosphere doubled. The neutrons released in the bombs reacted with the nitrogen in the air, creating a radioactive carbon, or carbon-14.
When the nuclear tests stopped, the levels of radioactive carbon went down. But it was already too late. The "bomb carbon" fell from the atmosphere to the surface of the ocean. Marine animals have been eating things in the ocean over decades and scientists have seen increased levels of carbon-14 since the bomb tests.
Researchers from China and the United States used the "bomb carbon" to trace organic material in organisms that live in deepest parts of the ocean. They studied crustaceans that live in hadal trenches, which are found 6,000 to 11,000 meters ( 20,000 to 36,000 feet) below the ocean's surface.
The crustaceans studied came from three trenches in the West Pacific Ocean. The conditions in these trenches are harsh -- the creatures that live there must adapt to extreme cold, high pressure and a lack of light and nutrients. The crustaceans scavenge and rely on dead organisms that fall to the ocean floor for food.
When researchers carbon-dated the crustaceans, they found the levels of carbon-14 in their muscle tissues were a lot higher than the levels of carbon found naturally in the deep ocean. Carbon-14 is found in almost all living things and is used to date the relative age of organisms in a process called carbon dating.
Normally, it'd take about 1,000 years for the ocean to circulate the bomb carbon into the deep sea. But, the ocean food chain carried the radioactive carbon faster than researchers expected.
"Although the oceanic circulation takes hundreds of years to bring water containing bomb [carbon] to the deepest trench, the food chain achieves this much faster," lead author Ning Wang, a geochemist at the Chinese Academy of Sciences in Guangzhou, China, said in a statement.
Researchers found that the crustaceans in these trenches live four times longer and grow larger than other crustaceans found in shallower waters. They also have a low tissue turnover rate. These deep-sea creatures lived to be more than 10 years old and grew to 3.6 inches long. Crustaceans in shallow water only live less than two years and grow to about 0.8 inches.
The creatures have been able to get so big and live so long as a side effect of living in such harsh conditions deep within the ocean, researchers said.
Living for so long, the amount of radioactive carbon had time to accumulate in the crustaceans' bodies, according to the study.
"It's mainly an indication that we have major influence in the deepest part of the ocean," Sun said. "I think we need to be careful that any human activity affects the whole Earth."