Researchers have uncovered new evidence that short-lived spikes in ocean phosphorus may have played a major role in two of the most severe marine extinctions in Earth's history.
Dr Matthew Dodd from The University of Western Australia's School of Earth and Oceans, was lead author of the study published in Nature Communications, which sheds new light on how nutrient disruption can destabilise life, climate and ocean chemistry on a global scale.
The study examined the Late Ordovician and Late Devonian mass extinctions, which occurred about 445 and 372 million years ago and wiped out about 85 per cent and 80 per cent of marine species respectively.
"Unlike several other major extinction events, both were associated with global cooling rather than warming, making their causes especially debated," Dr Dodd said.
Research analysed phosphorus in carbonate rocks from seven globally distributed rock sections, including key reference sections such as Anticosti Island in Canada, to reconstruct changes in ancient seawater phosphorus levels.
The data revealed brief, but consistent, phosphorus pulses coincided with biodiversity loss, widespread ocean anoxia and falling temperatures.
"We found that when the phosphorus cycle is disrupted, major impacts to climate and biodiversity can occur," Dr Dodd said.
"This is relevant now because human activity is again altering nutrient flows into the ocean, and the rock record shows just how consequential those changes can become."
The team also used biogeochemical modelling to test whether phosphorus surges could generate the kinds of environmental changes seen in the rock record.
The results showed that rising marine phosphorus could boost productivity, expand anoxia and help draw down atmospheric carbon dioxide, contributing to global cooling of up to around 5°C.
"What is striking is the ancient events we studied appear to have been linked to phosphorus-driven cooling, not greenhouse warming," Dr Dodd said.
"Today we are pushing the climate in the opposite direction through rapid carbon dioxide release, but the deeper lesson is the same: disturb a major biogeochemical cycle hard enough and it can contribute to environmental crises.
"Our findings provide one of the clearest links yet between marine nutrient disruption and ecological crisis in the ancient oceans, while also offering a reminder that changes to nutrient cycling can have far-reaching consequences for ocean health and environmental stability."
Co-author Professor André Desrochers, from the University of Ottawa, said the findings highlighted the tight coupling between ocean chemistry, climate and biodiversity during major extinction events.
"Anticosti Island in Quebec provides one of the most complete records of the Late Ordovician extinction," Professor Desrochers said.
"When integrated with other global sections, it plays a key role in revealing how Earth system processes were interconnected during this crisis."
