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Faraway current set off Mauna Kea glacier

A North Atlantic ocean system also caused more intense storms, a new study revealed

By Gary T. Kubota

POSTED:
LAST UPDATED: 01:36 a.m. HST, Aug 05, 2010


Slowing of the North Atlantic Ocean current system appears to be the reason for more frequent major storms and re-advancing of the glacial age in Hawaii 15,400 years ago, according to a new study.

"These connections are pretty remarkable -- a current pattern in the North Atlantic affecting glacier development thousands of miles away in the Hawaiian Islands," said Oregon State University professor Peter Clark, one of the study's authors.

Glaciers in Hawaii? Yes -- during and just after the last ice age, and the study is shedding light on modern planetary thermodynamics.

Some climate scientists believe global warming could eventually disturb the Gulf Stream in the Atlantic, creating colder temperatures in Europe and elsewhere.

University of Hawaii professor Axel Timmermann said the study confirms his research and that of other scientists that used climate models to predict that a weakening of certain North Atlantic currents would produce more westerly winds and intensified storms in Hawaii.

Timmermann said the study is also the first showing the effect of North Atlantic currents on the North Pacific.

"That's pretty spectacular," he said.

The study, supported by the National Science Foundation and published in the journal Earth and Planetary Science Letters, examined boulders deposited by an ancient glacier that once covered the summit of Mauna Kea.

The study presented more evidence that shutdown of North Atlantic currents 15,400 years ago had a global effect, including creating rainfall three times the current amount at the summit of Mauna Kea.

The research found that the glacier on Mauna Kea began to re-advance to almost its ice age size about 15,400 years ago, coinciding with a major slowdown of what scientists call the Atlantic meridional overturning circulation.

THAT CURRENT, known as AMOC, is part of a global ocean circulation system that carries heat from the tropics to the northern latitudes, a major reason that much of Europe is warmer in the winter than would be expected for its location.

The study concludes that the growth of the Mauna Kea glacier was a result of both colder conditions and a huge increase of precipitation on Mauna Kea caused by more frequent storms hitting the islands from the north.

"Mauna Kea had a large glacial ice cap of about 70 square kilometers until 14,500 years ago, which has now all disappeared," said Clark. "We've been able to use new data to determine specifically when, where and most likely why the glacier existed and then disappeared."

Mauna Kea is 13,803 feet above sea level and rises 30,000 feet from the sea floor, making it the tallest mountain in the world when measured from the ocean bottom.

Studies of past climate change indicate that the AMOC has slowed a number of times in surprisingly short periods, causing substantial cooling of Europe. The research was published by scientists from Oregon State University, the Woods Hole Oceanographic Institution, the University of British Columbia and the U.S. Geological Survey.

In a separate study, Timmermann and colleagues found that the North Pacific Ocean circulation system was completely different after the last ice age from it is today.

With Laurie Menviel of International Pacific Research Center and scientists in Japan and Belgium, Timmermann described the altered ocean circulation system based on computer modeling and radiocarbon data from 30 sediment cores at various North Pacific locations during the time the ice sheets melted 17,500 to 15,000 years ago.

Their findings were reported in a recent issue of the journal Science.

"What we basically identified is a completely new system of ocean circulation," Timmermann said in an interview.

The changes occurred about 17,000 years ago when the North Pacific surface water grew saltier, said Yusuke Okazaki of the Japan Agency for Marine-Earth Science and Technology, lead author of the paper.

The denser, saltier water sank, leading to a chain of events.

"Newly formed icy deep water spilled out of the sub-arctic North Pacific at depths of 2,000 to 3,000 meters, merging into a southward flowing deep western boundary current," Okazaki said in a release.

He said a warm, strong poleward current formed at the surface that "released much heat into the atmosphere" and supplied water for a "deep, overturning" circulation system that doesn't exist today.

The ancient system also may have stirred up old carbon-rich deep waters, contributing to the increase in atmospheric carbon dioxide, the scientists said.

"This could have catalyzed further warming and accelerated the glacial meltdown," Menviel said.

Timmermann said several factors came together to make the North Pacific saltier and take over the heat-pumping role.

First, he said, the breakdown of the ocean circulation in the North Atlantic caused a shift in Pacific rainfall patterns. This change in Pacific rainfall triggered a major shift in the North Pacific current system, making the North Pacific much saltier, he said.

"Very important also was that the Bering Strait was closed during this period 17,500 years ago. This kept the melted fresh water from flowing into the Pacific," he said. "These changes in the North Pacific may have buffered the global impacts of the collapsed circulation in the Atlantic and possibly prevented further cooling of the Northern Hemisphere."

That wouldn't happen today, because the Bering Strait is open.

"So if further melting, for instance, occurs now in Greenland," Timmermann said, "then some fresh water could spill out through the Bering Strait into the North Pacific." That means the North Pacific would not become salty enough to once again change course and prevent further cooling in the northern latitudes.

Star-Advertiser reporter Helen Altonn contributed to this report.






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