Hawaiian Glaciers Reveal Climate History

Clues found near the summit of Mauna Kea on the island of Hawaii suggest that changes in a far flung climate system had implications all over the world.

Boulders deposited on the summit of Mauna Kea by an ancient glacier have provided evidence of ancient glacier formation, a result of the most recent ice age, more frequent and violent storms in Hawaii’s past, and the impact of a distant climatic change.

“Mauna Kea had a large glacial ice cap of about 70 square kilometers until 14,500 years ago, which has now all disappeared,” said Peter Clark, a professor of geosciences at OSU. “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 one of the trick questions thrown out in friendly company. “What’s the tallest mountain on Earth?” you’ll ask, only to surprise your friends with the knowledge that it isn’t actually Mount Everest, but is in fact Mauna Kea, a massive volcanic mountain that rises up 30,000 feet from the ocean floor, and is in reality the tallest mountain on Earth.

It’s been dormant for thousands of years, but it once was home to a massive glacier at its peak, at the height of the last ice age 21,000 years ago. Naturally though, with warming conditions, the glacier began to recede soon after that.

The new research however has found that the glacier on Mauna Kea began to readvance to almost its ice age size about 15,400 years ago. (Mauna Kea is the only location in the north subtropical Pacific Ocean with signs of glaciation. Nearby locations such as Mauna Loa probably had evidence, but it was destroyed since by volcanic eruptions.)

It was at approximately that point in time that over in the North Atlantic Ocean a major slowdown of the Atlantic meridional overturning circulation (AMOC) occurred.

The AMOC is part of a global ocean circulation system that carries heat from the tropics to the North Atlantic. This transported heat is the primary reason that much of Europe is warmer in the winter than would be expected, given the latitude of the continent.

Studying past climate changes has found that the AMOC has cooled several times and in remarkably short periods of time, meaning that it is of great interest to climate scientists today. But the AMOC does more than just keep Europe cool, it seems, if it’s impact can be felt all the way over in Hawaii.

“The new data from Mauna Kea, along with other findings from geological archives preserved in oceans and lakes in many other areas, show that the decline of the AMOC basically caused climate changes all over the world,” Clark said. “These connections are pretty remarkable, a current pattern in the North Atlantic affecting glacier development thousands of miles away in the Hawaiian Islands.

“The global impact of the AMOC changes,” Clark added, “was just massive.”

The formation, size and movement of glaciers can provide valuable data, he said, because these characteristics reflect current and historic changes in temperature, precipitation or both.

The study conducted by scientists from the Oregion State University, the Woods Hole Oceanographic Institution, University of British Columbia and U.S. Geological Survey and published in the journal Earth and Planetary Science Letters found that the growth of the Mauna Kea glacier was caused by changes in the AMOC which cooled the temperature in the region combined with an increase in precipitation over Mauna Kea, up to three times as much as presently falls, which scientists believe could have caused more frequent cyclonic storm events.

Source: Oregon State University
Image Source: Randy Stewart

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