Friday, July 13, 2018

Scientists May Have Solved a Huge Riddle in Earth’s Climate Past.  It Doesn’t Bode Well for the Future.

An ancient flood seems to have stalled the circulation of the oceans, plunging the Northern Hemisphere into a millennium of near-glacial conditions.

Thirteen thousand years ago, an ice age was ending, the Earth was warming, the oceans were rising.  Then something strange happened – the Northern Hemisphere suddenly became much colder, and stayed that way for more than a thousand years.

For some time, scientists have been debating how this major climatic event – called the “Younger Dryas” – happened.  The question has grown more urgent:  Its answer may involve the kind of fast-moving climate event that could occur again.

This week, a scientific team made a new claim to having found that answer.  On the basis of measurements taken off the northern coasts of Alaska and Canada in the Beaufort Sea, the scientists say they detected the signature of a huge glacial flood event that occurred around the same time.

This flood, they posit, would have flowed from the Arctic into the Atlantic Ocean and shut down the crucial circulation known as the “Atlantic meridional overturning circulation” (or AMOC) – plunging Europe and much of North America back into cold conditions.

“Even though we were in an overall warming period, this freshwater, exported from the Arctic, slowed down the vigor, efficiency of the meridional overturning, and potentially caused the cooling observed strongly in Europe,” said Neal Driscoll, one of the study’s authors and a professor at the Scripps Institution of Oceanography.

The work, published in Nature Geoscience, was led by Lloyd Keigwin of the Woods Hole Oceanographic Institution along with researchers at that institution, Scripps and Oregon State University.

The result remains contested, though, with other researchers still arguing for different theories of what caused the Younger Dryas – including a very differently routed flood event that would have entered the ocean thousands of miles away.

Nonetheless, the story is relevant because today, we’re watching another – or rather, a further – deglaciation, as humans cause a warming of the planet.  There is also evidence that the Atlantic circulation is weakening again, although scientists certainly do not think a total shut-off is imminent, and are still debating the causes of what is being observed.

Either way, the new research underscores that as the Earth warms and its ice melts, major changes can happen in the oceans.  And could happen again.

The researchers behind the current study, working on board the U.S. Coast Guard Cutter Healy, analyzed sediments of deep ocean mud, which contain the shells of long-dead marine organisms called foraminifera.  In those shells the scientists detected a long-sought-after anomaly recorded in the language of oxygen atoms.

The shells contained a disproportionate volume of oxygen−16, a lighter form (or isotope) of the element that is found in high levels in glaciers.  That is because oxygen−16, containing two fewer neutrons and therefore lighter than oxygen−18, evaporates more easily from the ocean but does not rain out again as readily.  As a result, it often falls as snow at high latitudes and is stored in large bodies of ice.

“This is the smoking gun for fingerprinting glacial lake outbursts,” Driscoll said.  And that means the findings may also represent the trigger for the Younger Dryas.

Read more at Scientists May Have Solved a Huge Riddle in Earth’s Climate Past.  It Doesn’t Bode Well for the Future.

No comments:

Post a Comment