A team led by Professor Jordan Hemingway from ETH Zurich has for the first time directly measured the evolution of dissolved organic carbon (DOC) in the oceans over geological time.
The finding, published in Science, challenges traditional explanations about extreme glaciations and the emergence of complex life, providing new clues on how Earth responds to climate disturbances.
Ooids: Mineral Witnesses of the Primordial Ocean
Small stones of iron oxide reveal the history of marine carbon in crystalline layers.
Researchers used ooids, tiny spheres of iron oxide that grow in layers on the seafloor, as natural records of DOC.
By analyzing carbon impurities trapped in their structure, they were able to reconstruct the supply of organic carbon in the sea up to 1650 million years ago.
“Our results contradict all previous assumptions,” says Hemingway.
An Ocean with Less Carbon than We Imagined
Between 1000 and 541 million years ago, DOC was up to 99% lower than today.
The study reveals that during that period, the ocean contained between 90% and 99% less DOC than today. Only after the second oxygen catastrophe, levels increased to reach the current 660,000 billion tons.
This change coincides with the appearance of larger organisms, whose death accelerated marine carbon precipitation, but without deep recycling due to oxygen scarcity.
What is Dissolved Organic Carbon (DOC)?
An invisible reservoir that feeds bacteria, regulates the carbon cycle, and could influence future climate.
- Origin: comes from phytoplankton photosynthesis, microbial activity, and particle dissolution
- Ecological function: is the main food source for marine bacteria and archaea
- Climate reservoir: part of the DOC resists degradation and accumulates over millennia
- Carbon sequestration: acts as a sink, preventing carbon from turning into CO₂
Implications for Current Climate Change
The decrease in marine oxygen due to human activities could replicate past processes.
Although the events studied occurred hundreds of millions of years ago, researchers warn that current pollution and warming are causing a reduction in marine oxygen, which could repeat historical patterns of organic carbon loss and disrupt the climate balance.
“Understanding how Earth responds to disturbances is key, and humans are one of them,” says author Nir Galili.
