UW Today

April 29, 2015

Antarctic ice core shows northern trigger for ice age climate shifts

News and Information

Evidence trapped in ice cores from the West Antarctica Ice Sheet show a consistent link between abrupt temperature changes in Greenland and Antarctica during the most recent ice age. The findings, published April 30 in Nature, give scientists a clearer picture of how the ocean connects the northern and southern hemisphere climates.

closeup of ice

Freshly drilled ice core sticking out of the core barrel in January 2011.Mark Twickler, UNH

University of Washington scientists were part of a multi-institutional research team led by Nevada’s Desert Research Institute. The UW group used analyses of the oxygen in the water molecules in the ice to obtain the most precise record of Antarctica’s temperature history to compare temperature swings at the two poles. Eric Steig, a UW professor of Earth and space sciences, co-led the research paper with corresponding author Christo Buizert, a postdoctoral researcher at Oregon State University, and Joel Pedro, a former UW postdoctoral researcher now at the University of Copenhagen.

Ice cores analyzed in the 1990s at the UW and elsewhere confirmed that Greenland’s climate during the last ice age was very unstable, characterized by a number of large, abrupt changes in temperature. These so-called Dansgaard-Oeschger events took place every few thousand years, raising mean annual temperatures in Greenland and surrounding areas by about 5 degrees Celsius (9 degrees Fahrenheit) over just a few decades.

Meanwhile, temperatures in Antarctica showed an opposite pattern, with Antarctica cooling by a smaller amount at roughly the same time Greenland was warming. This suggests some type of global seesaw.

In the new paper, researchers find that the changes first appear in Greenland, and a response in Antarctica follows about 200 years later.

people in front of blue-tinged ice wall

Researchers inside a snow pit at the West Antarctic Ice Sheet drilling site in 2008.Kendrick Taylor, Desert Research Institute

Key to the result is the analysis of a new ice core from West Antarctica, drilled for five years ending in 2011 by the University of Wisconsin’s Ice Drilling and Design Operations and funded by the National Science Foundation. The core extends down 3.4 kilometers, or more than 2 miles.

“Past ice core studies did not reveal the temperature changes as clearly as this remarkable core,” Steig said.

Measurements of the core’s ice in the UW’s IsoLab, which Steig leads, documented a series of 18 temperature swings in Antarctica, each one corresponding with the abrupt Dansgaard-Oeschger events known from Greenland ice cores for the past 68,000 years. The technique uses the ratio of different forms of oxygen atoms in the ice core’s layers to deduce the air temperature when the snow was deposited.

The region where the core was drilled gets abundant snow, and so provides one of the most detailed records of Antarctic temperature. Greenland temperatures were already well established because of high annual snowfall and more available ice-core data.

The new work solves a classic chicken-and-egg problem in Earth’s climate history.

“Previous work was not precise enough to determine the relative timing of abrupt climate change in Antarctica and Greenland, and so it was unclear which happened first,” Steig said.

“Our new results show unambiguously that the Antarctic changes happen after the rapid temperature changes in Greenland,” he said. “It is a major advance to know that the Earth behaves in this particular way.”

The study was funded by the National Science Foundation and included almost 80 authors.

The opposing changes at the two poles suggested that something is redistributing heat between the northern and southern hemispheres.

“The 200-year lag that we observe certainly hints at an oceanic mechanism,” Buizert said. “The ocean is large and sluggish, thus the 200-year time lag is a pretty clear fingerprint of the ocean’s involvement.”

These past episodes of climate change differ from the changes now caused by carbon dioxide emissions, and probably could not happen today, Steig added, because they are related to the large ice sheets that once covered Canada and northern Europe.

Buizert said it is “very likely” that a major current in the Atlantic Ocean was involved in the abrupt climate reversals.The area off the coast of Greenland is where warmer water from the tropics cools and sinks to the bottom of the ocean, and is a “sweet spot,” he said, where the climate is very sensitive to changes in ocean circulation.

It so happens that Minze Stuiver, a UW professor emeritus of Earth and space sciences, made the same type of oxygen isotope measurements for the Greenland ice cores. That work in the early 1990s was critical in first demonstrating the speed of the Dansgaard-Oeschger climate changes, Steig said, and it is fitting that the new measurements were also made at the UW.

“We’ve come full circle in building on the seminal work that my graduate adviser conducted more than twenty years ago,” Steig said.

Other co-authors at the UW are graduate student Bradley Markle; postdoctoral researchers Spruce Schoenemann, Mai Winstrup and T.J. Fudge; research scientist Andrew Schauer; and professors Edwin Waddington and Howard Conway.

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For more information, contact Steig at steig@uw.edu. He is on sabbatical in Scotland and best initially contacted via email.

Part of this article was adapted from an Oregon State University press release. Photos are available here.

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