CORVALLIS, Ore. – Extensive marine ice covered the world’s oceans in the last ice age, which prevented oxygen from entering the ocean’s deep waters, complicating the relationship between oxygen and carbon, a new study has found.
“The sea ice is effectively like a closed window for the ocean,” said Andreas Schmittner, a climate scientist at Oregon State University and co-author of the paper. “The closed window keeps out fresh air; sea ice was a barrier to holding oxygen into the ocean, like hard air in a room full of people. If you open the window, you can oxygen from the outside enters and the air is not as stale. “
The findings, recently published in Geology of nature, to challenge previous assumptions about the relationship between oxygen and carbon dioxide in deep-sea waters. Understanding this relationship provides researchers with important insights into how the world’s oceans can cope with climate change, said Schmittner, a professor at OSU’s College of Earth, Ocean and Atmospheric Sciences .
The ocean plays an important role in the carbon cycle; carbon dioxide from the atmosphere dissolves in surface waters, where algae convert the carbon into organic matter. The release of that organic matter removes oxygen as carbon sinks into the deep ocean. The process of moving carbon from the ocean surface to the depth is called the biological pump.
Currently, the ocean is losing oxygen and this trend is expected to continue as oxygen flexibility decreases as the temperature warms. That would make scientists expect higher oxygen concentrations during the last ice age, when the oceans were colder, Schmittner said, but sediment previously collected below the seabed shows levels lower oxygen in the deep ocean in that time.
Researchers have previously theorized that the biological pump was stronger in the last ice age, increasing carbon sequestration. But that assumes that surface ocean oxygen is balanced by the atmosphere, Schmittner said.
In their new work, Schmittner and his colleagues, Ellen Cliff and Samar Khatiwala of Oxford University, used modeling to study the lowest oxygen levels in the deep ocean.
They found that disequilibrium played an important role in the carbon cycle. The oxygen density of the deep ocean was reduced by the fact that surface waters were less symmetrical with the atmosphere. The disequilibrium was largely due to the massive sea ice over the South Ocean, as well as higher iron fertilization from the ice-age atmosphere, which was more dusty, Schmittner said.
That means deep ocean oxygen levels are informed not only by the biological pumping process, but also by the sea ice, or lack thereof, just as room air quality can change. by opening or closing a window, he said.
The researchers’ approach to understanding the role of marine ice and other processes in ocean carbon and oxygen cycles could be applied to future climate modeling, Schmittner said.
“Conventional models cannot separate impacts from the biological pump on marine oxygen from marine ice or other effects,” he said. “This will change our understanding of the process and the reasons for these changes.”
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