A study suggests that the current loss of oxygen from the seas due to the climate crisis could be reversed in the future

June 28 () –

An international study led by Rutgers University in the United States suggests that the current loss of oxygen from the seas due to the heating of the water due to climate change could be reversed in the future, according to the researchers published in the journal ‘Nature’.

The work, which analyzes ocean sediments, shows that ocean oxygen levels in a key area were higher during the warm Miocene period, around 16 million years ago, when Earth’s temperature was warmer than it is today.

In the last decades, Oxygen levels in the ocean have been declining, raising fears of widening oxygen-deficient zones in key parts of the world’s oceans, further harming marine life.

Scientists have attributed this trend to rising temperatures induced by climate change, which affects the amount of oxygen that can be absorbed from the atmosphere.

“Our study shows that the eastern equatorial Pacific, which today hosts the largest oxygen-deficient zone in the oceans, was well oxygenated during the Miocene warm period, despite global temperatures at that time being higher than at the today,” says Anya Hess, lead author of the study and a Rutgers doctoral student working with Yair Rosenthal, Distinguished Professor of Earth and Marine Sciences in the Rutgers College of Arts and Sciences and College of Biological and Environmental Sciences. .

As he indicates, “this suggests that the current oxygen loss could ultimately be reversed.”

The fastest rates of oxygen loss in recent decades have been in oxygen-deficient areas, and they are expected to continue to expand and shallow, posing a threat to fisheries by reducing fish habitat. Without However, climate models diverge in their predictions of how these areas will respond beyond the year 2100, which inspired the team to investigate further.

To test current climate models, the researchers, from the United States, Germany and China, chose the middle Miocene, when climate conditions were similar to those predicted for centuries to come in the current era of climate change.

The researchers examined oceanic sediments deposited during the middle Miocene in the eastern equatorial Pacific. The sediments were recovered from the seafloor by scientists aboard the National Science Foundation-funded research vessel JOIDES Resolution as part of what is now known as the International Ocean Discovery Program (IODP).

They isolated the fossilized remains of microorganisms the size of a grain of sand that live in the water column called foraminifera and analyzed the chemical composition of the foraminifera, which reflects the chemical profile of the ancient ocean.

They differentiated the oxygen levels of the ancient oceans in a number of ways, including using nitrogen isotopes — forms of the element that have different relative atomic masses — as detectors. The isotopes are sensitive to a process called denitrification that only occurs at very low oxygen levels. They also used an analysis method that compares iodine and calcium levels and gives subtle readings that can differentiate between well-oxygenated conditions and moderately well-oxygenated conditions.

The methods showed that the area was well oxygenated during the height of the Miocene heat, approaching even today’s levels seen in the open-ocean South Pacific.

“These results were unexpected and suggest that the solubility-driven loss of oxygen that has occurred in recent decades is not the end of the story of the oxygen response to climate change.“, notes Rosenthal.