Ice Age Carbon Came Not from the Pacific

A new study has found that the Northeast Pacific was not an important reservoir for the carbon that is believed to be responsible for the end of the last Ice Age, throwing scientists back to the proverbial drawing board as they digest this shift in their theories.

This view of Earth’s horizon as the sunsets over the Pacific Ocean was taken by an Expedition 7 crewmember onboard the International Space Station (ISS).

The study, published by the National Science Foundation and the University of Michigan in the online version of the journal Nature Geoscience, used detailed radiocarbon dating of foraminifera  from a sediment core extracted from the Gorda Ridge off the coast of Oregon.

“Frankly, we’re kind of baffled by the whole thing,” said Alan Mix, a professor of oceanography at Oregon State University and an author on the study. “The deep North Pacific was such an obvious source for the carbon, but it just doesn’t match up. At least we’ve shown where the carbon wasn’t; now we just have to find out where it was.”

Scientists had long assumed that the ocean – currently home to 90 percent of the Earth’s readily exchangeable carbon – was responsible for expelling the carbon that ended the last Ice Age. However their research actually showed that the ventilation age in the Gorda Ridge – or, the amount of time since deep water was last in contact with the atmosphere – was breaking their hypotheses.

“We were surprised to find that during the last ice age, the deep Northeast Pacific had a similar ventilation age to today, indicating it was an unlikely place to hide the missing carbon,” said David Lund, a paleoceanographer at the University of Michigan, formerly at Oregon State, and lead author on the Nature Geosciences paper.

“This indicates that the deep Pacific was not an important sink of carbon during glacial times. Even more intriguing is that we found the ventilation age increased during the deglaciation, at the exact time that atmospheric CO2 levels were rising.”

For more information on the research conducted by Mix, Lund, and their colleagues, head on over to the Oregon State University website.

This study, along with sending scientists back to the drawing board to understand the end of the last Ice Age, helps understand how the Earth may respond to future changes in climate.

The Earth “breathes carbon in and out,” Mix said, inhaling carbon into sediment and soils, while exhaling it via volcanism and a slow exchange between the oceans, soils and plant life with the atmosphere.

When everything is in balance, the Earth is said to be in a “steady state.” But on numerous occasions in the past, the carbon balance has shifted out of whack.

“Because the ocean is such a huge repository of carbon, a relatively small change in the oceans can have a major impact,” Mix said. “We know ocean circulation changed during the ice ages and that is why many scientists assumed the deep Pacific Ocean was the source for rising CO2 levels during the last deglaciation.”

Lund said it “is conceivable that we are misunderstanding the radiocarbon signal by assuming it is controlled by ocean mixing.”

“These are volcanically active regions, so the input of carbon from volcanoes, which lacks radiocarbon because of its great age, needs to be looked at,” Lund pointed out. “But it is premature to draw any conclusions.”

Image Source: NASA

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