Scientists have found traces of radioactive carbon in marine organisms that inhabit the Mariana Trench, the deepest spot on Earth. The radioactive carbon was released into the atmosphere from 20th-century nuclear bomb tests. Organisms at the ocean surface have incorporated the bomb carbon into the molecules that make up their bodies since the late 1950s.
The crustaceans in deep ocean trenches are feeding on organic matter from these organisms when it falls to the ocean floor. The results also help scientists to understand how creatures have adapted to living in the nutrient-poor environment of the deep ocean.
The studied the crustaceans live for an unexpectedly long time by having extremely slow metabolisms, which they suspect may be an adaptation to living in this impoverished and harsh environment.
How did Radioactive particles mix in the ocean?
Carbon-14 is a radioactive carbon that is created naturally when cosmic rays interact with nitrogen in the atmosphere. Carbon-14 is much less abundant than non-radioactive carbon, but scientists can detect it in nearly all living organisms and use it to determine the ages of archeological and geological samples.
Thermonuclear weapons tests conducted during the 1950s and 1960s doubled the amount of carbon-14 in the atmosphere when neutrons released from the bombs reacted with nitrogen in the air. Levels of this bomb carbon peaked in the mid-1960s and then dropped when atmospheric nuclear tests stopped. By the 1990s, carbon-14 levels in the atmosphere had dropped to about 20% above their pre-test levels.
This bomb carbon quickly fell out of the atmosphere and mixed into the ocean surface. Marine organisms that have lived in the decades since this time have used bomb carbon to build molecules within their cells, and scientists have seen elevated levels of carbon-14 in marine organisms since shortly after the bomb tests began.