Arctic currents change as ancient Pacific did

Changes in Arctic currents today appear to reflect similar changes thousands of years ago – in the North Pacific. Scientists think they may be linked.

LONDON, 26 April, 2018 – The recent discovery that Arctic currents have weakened significantly appears in some ways to be a repeat of what happened the other side of the Arctic in the distant past.

Thousands of years ago the circulation of the North Pacific ocean changed  substantially, releasing large quantities of carbon dioxide to the atmosphere, scientists in Scotland have found.

The change they have identified helped to warm the planet and to end the last Ice Age. It happened about 15,000 years ago, though, so it should be of little concern to us today – except for one factor.

Several weeks ago an international scientific study published new and harder evidence that one of the planet’s key heat pumps, the currents which exchange warmth between the tropics and the Arctic, are weaker today than at any time in the last millennium.

“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. This will have a huge effect on the climate system”

While earlier studies of northern ocean currents had relied on computer simulations, this later study is different: it is based on direct observation of what is actually happening in the Atlantic and Arctic oceans.

And what’s happening there now is not markedly different from what took place long ago in the North Pacific. The researchers think their findings are strong enough to suggest a possible link, one which if established could have essential information for this generation.

The Scottish study, published in the journal Nature Geoscience, also found that the changes in circulation resulted in a reduction of the amount of oxygen in the deep ocean. The findings will help scientists to understand the processes controlling the exchange of CO2 and oxygen between the ocean and atmosphere.

The researchers measured the chemical composition of the shells of tiny fossil plankton, called foraminifera, which they used to reconstruct the exchange of CO2 between the North Pacific ocean and atmosphere at the end of the last Ice Age, when carbon dioxide levels in the atmosphere increased.

Circulation change

They found that the North Pacific had released large amounts of CO2 to the atmosphere around 15,000 years ago, when ocean currents in the Atlantic were also changing rapidly.

Their findings showed that the release of CO2 by the North Pacific was caused by a change in its circulation and could explain a drop in oxygen levels in the Pacific which occurred at the same time and was first discovered over 20 years ago. Scientists are seeing a similar loss of oxygen from the ocean as the climate changes today.

The lead author, Dr Will Gray, from the School of Earth and Environmental Sciences at the University of St Andrews but formerly of University College London, said the new studies showing that ocean currents in the North Atlantic were slowing down were “worrying”.

He said: “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. 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.

Future need

“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.”

US scientists found several years ago that in a single decade the North Atlantic had increased by 50% the rate at which it was absorbing CO2 from human activities.

Dr Gray’s co-author Dr James Rae, also from the University of St Andrews, said that although the ancient North Pacific CO2 rise was dramatic in geological terms, it happened very slowly compared to modern man-made CO2 rise.

“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”, he said. “This will have a huge effect on the climate system, and one that we are only just beginning to see.”