A team of international scientists has uncovered evidence that the tropical Pacific Ocean may be more resilient to global warming than previously feared.

The study, co-led by Patrick Rafter of the University of South Florida, analysed nitrogen isotopes preserved in microscopic plankton fossils to reconstruct ocean conditions during the Pliocene Epoch, between 5.3 and 2.6 million years ago. At that time global temperatures were comparable to today.

The results indicate that nitrate concentrations in the eastern tropical Pacific, a key driver of plankton blooms and marine food chains, did not decline during past periods of warming. This challenges earlier models that warned of a collapse in fisheries as the region heats.

“Our measurements suggest that, on a warmer planet, the availability of marine nutrients to fuel plant growth and fisheries may not necessarily decline,” Rafter, a chemical oceanographer at USF’s College of Marine Science, said.

Nutrient upwelling in the Pacific supports some of the world’s most productive fisheries. During El Niño events this process weakens, reducing nutrient supply and damaging ecosystems. Previous studies suggested such conditions could become permanent in a hotter world, but the new findings point to greater long-term stability.

The research relied on detailed laboratory work. Scientists from USF, the University of Massachusetts Boston, the University of California Irvine and Princeton University hand-sorted shells of tiny plankton called foraminifera from deep-sea cores. The fossils were dissolved and their nitrogen isotopes analysed with the help of bacteria.

“We have used this nitrogen isotope like a geochemical fingerprint,” Rafter said. “We do not have a time machine, but we can use our detective toolkit to reconstruct what happened in the ocean the last time Earth was as warm as today.”

Co-lead author Jesse Farmer of UMass Boston said the results provide cautious optimism. “Our current warming is happening so quickly that the ocean may behave differently than it does when it has been warm for a long time, as was the case in the Pliocene,” he said. “It is good news that the nutrient supply to the eastern Pacific food web will be maintained in a warmer ocean, but modern threats like acidification and overfishing remain.”

The team plans to expand its methods to other parts of the ocean in the hope of building a clearer picture of how marine ecosystems will respond to climate change.

The research has been published in Science.