Oxygen is fundamental to sustaining life on Earth. The ocean gets its oxygen from its upper layers through contact with the atmosphere. As our planet continues to warm, the ocean is slowly losing its ability to absorb oxygen, with dire consequences for marine ecosystems and the human activities that depend on them. Although these trends will continue into the future, it is not yet clear how oceanic oxygen will be redistributed throughout the ocean interior, where ocean currents and biodegradation of biomass dominate atmospheric diffusion.

“Marine sediments are the ocean’s history book. By studying past periods of time in which temperatures rose rapidly, we can gain valuable insight into how ocean oxygen and organisms changed climate. how it responded to the changes,” said Simon Moretti, its lead author. Now published in a research journal. science.

Using a combination of chemical and morphological measurements on Fominifera, microscopic fossils preserved in marine sediments over millions of years, a team of researchers led by scientists from the Max Planck Institute for Chemistry in collaboration with Princeton University has mapped the response to tropical ocean oxygenation. has been rebuilt. PETM

Nitrogen isotopes and fossil size reflect the amount of oxygen in seawater.

Nitrogen isotopes preserved within fossil foraminifera enabled scientists to track past changes in water column denitrification. This process, in which nitrate molecular nitrogen (N2) by bacteria, found only in the most oxygen-deficient waters of the ocean: the anoxic zone. “Our measurements show that, contrary to most expectations, denitrification decreased during the PETM,” said Alfredo Martínez García, head of the laboratory at MPIC. During this interval, the oxygen-depleted areas of the ocean shrank.” was studied.

In addition, the size of foraminifera fossils proved to be a fundamental part of the puzzle. Models that describe the metabolism of marine organisms allow their body size to be related to the environmental temperature and oxygen content of the water in which they live. A reduction in body size is an effective adaptation to a warming climate, as it allows organisms to lower their metabolism. in times of stress. “Remarkable, and unexpected, evidence suggests that planktonic foraminifera from the central tropical Pacific increased during the warming of the PETM, increasing tropical oxygenation in the upper layers of the ocean,” said Curtis Deutsch, at Princeton University. Professor of Geosciences commented. who co-authored this study. Planktonic foraminifera live in the upper layers of the ocean, as opposed to the lower layers.

Increasing oxygen levels could reduce mass extinctions in the upper ocean.

The finding that oxygen levels in the tropical ocean increased rather than decreased during PETM warming also gives researchers clues to another puzzle, changes in marine biodiversity. The PETM was the largest extinction event among deep-sea organisms during the Cenozoic Era, which spanned the last 66 million years. One of the many mysteries surrounding the PETM is that while this mass extinction event unfolded at greater depths, organisms living in the upper ocean were less affected. “Our study shows transient tropical oxygenation has helped maintain habitats despite major temperature stress,” said Simone Moretti. “However, during the PETM the fauna of the surface ocean was greatly affected, and it took more than a hundred thousand years for these ecosystems to return to their original state, which is an eternity in the time of human civilization. “