A Rutgers study published in Nature, which analyzes ocean sediment, shows that ocean oxygen levels in a key region were higher during the Miocene Warm Period, about 16 million years ago, when Earth’s temperature was warmer than today.
In recent decades, the level of life-sustaining oxygen in the ocean has been declining, raising concerns that oxygen-deficient zones in key parts of the world’s oceans will expand and further harm marine life.
Scientists attribute this trend to rising temperatures caused by climate change, which affect the amount of oxygen that can be absorbed from the atmosphere.
“Our study shows that the eastern equatorial Pacific, which is now home to the largest oxygen-deficient zone in the oceans, was well oxygenated during the Miocene warm period, despite the fact that global temperatures at that time were higher than today,” he added. said Anya Hess, the study’s lead author and a Rutgers doctoral student working with Yair Rosenthal, a distinguished professor of marine and earth sciences with the Rutgers School of Art and Sciences and the School of Environmental and Biological Sciences.
Hess added: “This suggests that the current oxygen loss may eventually be reversed.”
Climate models differ in their predictions
The most rapid oxygen losses in recent decades have been in oxygen-deficient zones, and they are expected to continue to expand and become shallower, threatening fisheries by shrinking fish habitat. However, climate models differ in their predictions of how these zones will respond after 2100, inspiring the team to investigate further.
To test current climate models, the researchers chose the middle Miocene, when climate conditions were similar to those predicted for the next few centuries 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 sea floor by scientists aboard the National Science Foundation-funded research vessel JOIDES Resolution, part of what is now known as the International Ocean Discovery Program (IODP).
Scientists have isolated the fossilized remains of microorganisms the size of individual grains of sand that live in the water column called foraminifera. The scientists analyzed the chemical composition of the foraminifera, which reflects the chemical profile of the ancient ocean. They detected oxygen levels in the ancient oceans in several ways, including using nitrogen isotopes forms of the element that have different relative atomic weights — as detectors.
The methods showed that the area was well oxygenated during the peak Miocene warmth, even approaching levels seen today in the open ocean of the South Pacific.
“These results were unexpected and suggest that the dissolution-driven loss of oxygen that has occurred in recent decades is not the end of the story of oxygen’s response to climate change,” Rosenthal said.
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References: https://www.sciencedaily.com/releases/2023/06/230628125214.htm
