Sea ice forming slowly and quietly in coastal regions may be behind it all.
That is, that briny ice is one of the main drivers of circulation deep in the ocean, and influences climate regionally and worldwide--although it isn't reflected well in current global climate models. A paper on that topic was recently accepted for publication in the journal Paleoceanography.
Researchers from University of California Santa Cruz (UCSC) and elsewhere analyzed sediment cores from the Bering Sea that show the last 1.2 million years of ocean circulation in the North Pacific, for the study.
"Coastal sea ice formation may be important to future climate change because the arctic and subarctic regions are warming at twice the rate of other parts of the world," said Karla Knudson, a graduate student in Earth and planetary sciences at UCSC and the paper's lead author, in a release.
The formation of sea ice causes salt to expel into nearby water. As a result, the water becomes more dense and sinks to the depths, bringing oxygen with it. Cold deep water flows toward the equator and warmer water on the surface moves toward the poles. The "overturning circulation" that results moves heat around the Earth.
"It helps to modulate the climate by transferring heat from the equator to the poles," said coauthor Christina Ravelo, professor of ocean sciences, UCSC, in the release.
That process is also called "thermohaline circulation" and has received more focus in the North Atlantic than in the North Pacific. The North Atlantic Deep Water is known to be a strong impetus of circulation and climate throughout the world. The North Pacific Intermediate Water system, conversely, is not as large a driver as the North Atlantic, but is very important regionally nonetheless.
The study looked at sediment cores from the Bering Sea that had been collected in 2009. The 1.2 million years of oceanographic records in those went back much later than other existing records from that region. In them, the scientists saw a wide range of climates, from glacial periods to ice sheets to moderate times more like the weather of today.
The cores revealed that the Bering Strait was a key part of the record, and that when the Strait was closed, overturning circulation was strong in both oceans. Basically, the sea ice that formed in the Bering Sea produced vitally strong brine, confirmed a release.
Today, the Sea of Okhotsk is the source of much of the North Pacific Intermediate Water. But it's still important to look further at the formation of sea ice and brine on the coastal shelves, wherever it happens.
"These small-scale processes might be important to understanding the full impact of climate change," Ravelo said in the release. "As the climate gets warmer, we could see reduced sea ice formation in the Sea of Okhotsk and the Arctic. So it would be nice for the climate models to have sufficient resolution to be able to predict the impact of changes in coastal sea ice."
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