Radioactive carbon created as a by-product of nuclear bomb tests has reached the deepest parts of the ocean — and is ending up inside marine creatures.
This finding by Chinese researchers shows just how quickly human pollution can enter the food chain and find its way down to the deep ocean.
However, this bomb carbon is helping scientists to learn more about how marine life manages to get by in such cold, dark, deep and nutrient-poor environments.
They found that tiny marine crustaceans can live far longer than their shallow water counterparts and grow to a much larger size.
This is likely because the animals have evolved extremely slow metabolisms as an adaptation to living in the extreme conditions found in deep oceanic trenches.
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Radioactive carbon created as a by-product of past nuclear bomb tests (pictured, stock image) has reached the deepest parts of the ocean — and is ending up inside marine creatures
Researchers led by Chinese Academy of Sciences geochemist Ning Wang used traces of carbon from nuclear bombs to analyse deep sea amphipods, tiny marine crustaceans that live by scavenging dead organisms and marine detritus.
The animals were collected in 2017 from three trenches in the west Pacific Ocean — Mariana, Mussau and New Britain — down to depths of up to 7 miles (11 kilometres) below the ocean’s surface.
Experts were surprised to discover that the carbon-14 levels in the amphipods’ muscles were much greater than those found in organic matter floating around in deep waters.
Analysing the contents of the animal’s guts, they then found that the levels of bomb-derived carbon was also high and matched the levels of carbon-14 found in organic materials near the surface of the Pacific Ocean.
These findings suggest that amphipods are selectively feeding on detritus that has fallen to the seafloor from the ocean’s surface, rather than taking in the more local sources of carbon found deposited in nearby sediments.
‘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,’ said Ms Wang.
The findings are helping researchers to understand how creatures like amphipods have adapted to living in the deepest parts of the ocean, which lie over 4 miles (6 kilometres) below the ocean’s surface, in what is called the hadal zone.
Abysses this deep are only found within ocean trenches, narrow depressions in the shape of the sea floor that are formed where one of the Earth’s tectonic plates is subducting under another.
The animals which call these trenches home must be adapted to live under intense pressures and extremely cold temperatures, as well as be able to cope with the lack of light and available nutrients.
Ms Wang and colleagues found that the amphipods that live in these three deep ocean trenches tend to both grow larger and live longer than their counterparts.
Researchers used traces of carbon from nuclear bombs to analyse amphipods (pictured), tiny marine crustaceans that live by scavenging dead organisms and marine detritus
Amphipods living in shallow waters typically live for less that two years, and reach an average length of about 0.8 inches (2 centimetres).
However, researchers found that amphipods in the deep ocean trenches grew to be over 10 years old and as big as 3.6 inches (9.1 centimetres) long.
The scientists believe that the deep-living amphipods’ size and longevity can be credited to the same evolutionary adaptations that allow them to live in such cold, high pressure, nutrient-poor environment.
A slow metabolism and low cell replacement rate would allow the tiny crustaceans to store energy over long periods of time.
However, this same longevity would also likely mean that pollutants have the opportunity to accumulate to greater levels in these unusual creatures.
This ‘bring[s] more threat to these most remote ecosystems,’ Ms Wang said.
Amphipods were collected from three trenches in the west Pacific Ocean — Mariana, Mussau and New Britain — down to depths of up to 7 miles (11 kilometres) below the ocean’s surface
‘There’s a very strong interaction between the [ocean] surface and the bottom, in terms of biologic systems,’ added paper co-author Weidong Sun, who is a geochemist at the Chinese Academy of Sciences in Qingdao.
‘Human activities can affect the biosystems even down to 11,000 meters, so we need to be careful about our future behaviours.’ he said.
‘It’s not expected, but it’s understandable, because it’s controlled by the food chain.’
‘What is really novel here is not just that carbon from the surface ocean can reach the deep ocean on relatively short timescales,’ said Rose Cory, an earth scientist from the University of Michigan who was not involved in the study.
Instead, she continued, the main novelty lies in how ‘the young carbon produced in the surface ocean is fuelling, or sustaining, life in the deepest trenches,’ Cory said.
The full findings of the study were published in the journal Geophysical Research Letters.
WHAT IS CARBON-14?
Carbon-14 is produced by nuclear tests, such as this one, in Nevada, in 1957
Carbon-14 is a radioactive isotope of carbon.
It is far less common that its non-radioactive counterpart.
Both carbon forms are found in living organisms, albeit in different amounts.
Experts use the two isotopes together to calculate the ages of archaeological and geological samples.
Carbon-14 is created naturally when cosmic rays interact with nitrogen in the atmosphere.
But it can also be created artificially as a product of nuclear explosions, when neutrons released by atomic bombs collide with atmospheric nitrogen.
Nuclear weapons testing in the 1950s and 60s saw levels of carbon-14 in the atmosphere temporarily double.
Levels quickly fell when the testing ceased and, by the 1990s, had returned to only 20 per cent above their pre-nuke amounts.
Bomb carbon from the atmosphere fell into surface of the ocean.
Here, it has been absorbed by marine creatures and incorporated into their bodies.
As a consequence, scientists began finding increased levels of carbon-14 in sea creatures shortly after the first bomb tests began.
