Shift in ocean circulation triggered the end of the last ice age

The end of the last ice age was precipitated by a shift in the circulation of the North Pacific Ocean some 15,000 years ago.

According to new research by scientists at the University of St. Andrews, the altered circulation released large amounts of CO2 into the atmosphere, warming Earth's climate.

Scientists modeled the ancient shifts in circulation and ocean-atmosphere gas exchange by measuring the chemical composition of foraminifera, the tiny fossil shells left behind by plankton. Their analysis -- published this week in the journal Nature Geoscience -- revealed an uptick in the amount of CO2 released by the North Pacific beginning 15,000 years ago. Previous studies have found evidence of shifting circulation patterns in the Atlantic at roughly the same time.

Earlier this month, another group of researchers published a study showing the Atlantic's circulation is slowing down. Scientists suggest a slowdown could significantly alter climate patterns across the globe.

"In our study we see very rapid changes in the climate of the North Pacific that we think are linked to past changes in ocean currents in the Atlantic," lead researcher Will Gray, an environmental scientist at St. Andrews, said in a news release. "This gives us an example of the way that different parts of the climate system are connected, so that changes in circulation in one region can drive changes in CO2 and oxygen all the way over on the other side of the planet."

Gray and his colleagues also found shifting North Pacific circulation patterns have led to a reduction in the amount of oxygen in the deep ocean. Previous studies have shown regions of low-oxygen and no-oxgyen in Earth's oceans are growing in size and number.

For climate scientists, understanding the exchange of CO2 between Earth's oceans and atmosphere is essential to accurately modeling climate change.

"The North Pacific Ocean is very big and just below the surface the waters are brimming with CO2; because of this, we really need to understand how this region can change in the future, and looking into the past is a good way to do that," Gray said.

While natural shifts in ocean circulation and ocean-atmosphere gas exchange fueled relatively dramatic climate change at the end of the last ice age, scientists say those changes happened much slower than man-made climate change.

"Humans have driven CO2 rise in the atmosphere as large as the CO2 rise that helped end the last Ice Age, but the man-made CO2 rise has happened 100 times faster," said St. Andrews researcher James Rae. "This will have a huge effect on the climate system, and one that we are only just beginning to see."

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Washington DC (UPI) Apr 16, 2018
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