Study links Arctic chemistry shift to ancient heatwave

A Chinese-led research team has shed new light on how the Arctic Ocean may have intensified one of Earth's most dramatic warming episodes 56 million years ago — a discovery that could carry a warning for today's climate.

The study, led by Zhang Yige of the Chinese Academy of Sciences' Guangzhou Institute of Geochemistry, was published Thursday in the journal Nature Geoscience. It focuses on the Paleocene-Eocene Thermal Maximum (PETM), a period of extreme heat and ocean acidification that has long intrigued scientists for its parallels to modern climate change.

Researchers found that the Arctic's chemical balance was a key player. In today's oceans, microbes usually act like a "slow-burning power plant", using sulfur compounds to break down methane. This process not only keeps the potent greenhouse gas from escaping but also helps counteract acidification.

But 56 million years ago, sulfate levels in Arctic seawater were less than one-third of what they are today. Without enough "fuel", the normal methane-eating microbes sputtered out. Oxygen-loving bacteria took over instead, burning through methane quickly and releasing carbon dioxide in the process — more like a furnace belching smoke than a steady stove.

That chemical switch may have turbocharged the warming of the PETM. And with the modern Arctic warming and freshening rapidly, researchers caution that similar conditions could re-emerge. If so, the region could shift from storing methane safely to releasing it in large bursts, with serious consequences for the global climate.