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Ice Core Shows North American Ice Sheet's Retreat Affected Antarctic Weather

2018-02-07 00:00:00

Researchers at the University of Washington were among the co-authors of a new study that uses ice core data to see how Earth’s climate behaved at the end of the last ice age, when the Laurentide Ice Sheet covering much of North America retreated about 16,000 years ago.

iceberg from above

Sea ice and icebergs in the Southern Ocean in 2017 off the coast of West Antarctica. The new study looks at the year-to-year variability of storms in this region. Bradley Markle/University of Washington

The study led by the University of Colorado Boulder is published online this week and will be in the Feb. 15 print issue of the journal Nature.

“Our data are from just one location in Antarctica, but the results provide an indication of how climate variability changed across most of the Southern Hemisphere -- and perhaps most of the globe -- as the Northern Hemisphere ice sheets receded at the end of the ice age,” said co-author Eric Steig, a UW professor of Earth and space sciences.

The study relies on information contained in a 2-mile core of ice from the West Antarctic Ice Sheet that UW researchers helped to drill from 2006 to 2011. This ice core is the first continuous climate record to preserve year-to-year climate variability of the last 30,000 years.

ice core closeup

The West Antarctic Ice Sheet Divide Ice Core during the drilling project.Bradley Markle/University of Washington

At the Stable Isotope Lab in Boulder, the researchers slowly melted and then vaporized the ice cores for analysis using laser absorption spectroscopy, a new methodology that reveals the isotopic composition of the water with unprecedented speed, detail and accuracy. The isotopic composition of the ice core is a measure of the chemical composition of ancient snowfall in Antarctica.

Changes in the isotopic composition through time reflect changes in climate; they are driven by changes in temperature, snowfall amount and atmospheric circulation. The measurements at Boulder were independently corroborated by analyses in the UW’s Isolab.

The isotopic records preserved in the layers of ice show a large, abrupt decline in year-to-year and decade-to-decade variability about 16,000 years ago, indicating a decline in the variability of climate.

More photos from Markle’s field research

CU Boulder press release: “North American ice sheet decay changed Antarctic climate

“Year-to-year and decade-to-decade climate in Antarctica was extremely variable during the ice age. One year would not necessarily be as similar to the next as it is today,” said co-author Bradley Markle, a UW postdoctoral researcher in Earth and space sciences who contributed to the new paper as part of his UW doctorate. “Our study shows that changed abruptly at the end of the ice age. The scale of this variability was cut nearly in half.”

The researchers next used climate models to determine the reason for the observed change. They found that it was largely caused by the shrinking of the Laurentide Ice Sheet, which affected atmospheric conditions near the equator.

“When the North American ice sheet receded and disappeared, it changed how the atmosphere in the tropics influenced the storms around Antarctica. The tropics, counterintuitively, exert a strong influence on the storminess around Antarctica through phenomena like El Ni?o,” Markle said. “As different as they seem, the cold Antarctic and the warm tropics are intimately connected.”

The new study adds to a growing body of research -- including previous studies from the UW -- showing connections between climate in different parts of the planet. This is one of only a small handful of studies to make such a connection this far back on the shorter timescales that humans experience.

“The results demonstrate how seemingly localized effects in one part of the world may have a large impact on climate elsewhere on Earth,” said lead author Tyler Jones, a postdoctoral researcher at the University of Colorado Boulder.

The research and drilling project were supported by the National Science Foundation. Other co-authors are William Roberts, who completed his doctorate at the UW and is now at the University of Bristol; Kurt Cuffey, who completed his doctorate at the UW and is now at the University of California, Berkeley; and James White at the University of Colorado, Boulder.

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For more information, contact Steig at esteig@uw.edu or 206-685-3715, Markle at marklebr@uw.edu and Jones at 303-492-4606 or tyler.jones@colorado.edu.

Parts of this article were adapted from a CU Boulder press release.

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