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KU Radar Research Provides Significant Input to Climate Study in Nature

Thursday, January 24, 2013

A collection of breakthrough discoveries that provide new details on changes in the Earth’s climate from more than 100,000 years ago — made possible in part by a team of researchers from the University of Kansas — is featured in the most recent issue of one of the world’s most prestigious scientific journals.

The Jan. 24 issue of Nature contains an article on the findings from a deep ice core drilled in northern Greenland, at a camp known as the North Greenland Eemian Ice (NEEM) drilling camp. Research at the drill site is led by the Center for Ice and Climate at the University of Copenhagen, which partners with the KU-led Center for Remote Sensing of Ice Sheets (CReSIS).

“It’s great that this paper got accepted in such a prestigious publication,” said Dorthe Dahl-Jensen, leader of the Center for Ice and Climate. “It shows what a great team of researchers we have assembled and how valuable these findings are.”

Research at the NEEM site centers on climate data contained in layers of ice 1.5 miles deep, brought to the surface in 3-foot chunks through a hollow, 4-inch-wide tube during parts of three summers from 2008 to 2010. Data being analyzed reveal key information about global temperatures, sea-level rise and changes to polar ice sheets during what is known as the Eemian period, which began about 130,000 years ago and ended about 114,000 years ago. The period bridged two ice ages and is known for warm temperatures worldwide.

The climate graph shows the temperature from the previous warm interglacial period, the Eemian (left) throughout the entire ice age to present time. The blue colours indicate ice from a cold period, while the red colour is ice from a warm period. The new results show that during the Eemian period, 130 to 115 thousand years ago, the climate in Greenland was around 8 degrees C warmer than today. The early Eemian, 128 to 122 thousand years ago, coincides with strong northern summer insolation as shown below the climate curve. The top shows a graph of ice sheet surface temperature and altitude. At the beginning of the Eemian, 128,000 years ago, the ice sheet in northwest Greenland was 200 meters higher than today, but during the warm Eemian period the ice mass regressed, so 122,000 years before now the surface had sunk to a level of 130 meters below the current level. During the rest of the Eemian the ice sheet remained stable at the same level with an ice thickness of 2,400 meters.

“From the findings within the ice core samples, we now know the Eemian period was four to eight degrees warmer than today. We already knew it was warmer, but an eight-degree spike is higher than we realized. We’ve never had data this clear or accurate,” said Dahl-Jensen.

Beyond the information contained within the small samples of ice brought to the surface for further study, Dahl-Jensen’s group relies on radars designed by KU’s CReSIS team to geographically extend these results for modeling larger areas of the ice sheet.

“The first and most important parameter to modeling an ice sheet is knowing where the bedrock is, and the radar from CReSIS detects that beautifully,” Dahl-Jensen said. “The radar detects a lot of internal layering and provides a clear picture of climate transitions over time. By analyzing these images, we can determine the conditions and the age of the ice over a large area.”

The Nature article praises KU’s CReSIS team, noting:

“The consistency of the radar images and deep ice core results at NEEM is a breakthrough result, and it demonstrates that radar imaging can now be used to predict folded ice layering. This opens the potential for a systematic reconstruction of the Eemian Greenland ice sheet layering from new radar imaging. Assimilation of such data in ice sheet models should lead to much improved histories of the configuration of the ice sheet in the past, improving our ability to predict the future evolution of the ice sheet.”

A commitment to innovation has fueled CReSIS’ success in remote sensing.

“We have substantially improved the sensitivity and capability of radars used to sound ice and image the ice bed at CReSIS over the last few years, and this is resulting in data that are very useful for a wide range of glaciological studies, including the interpretation of ice cores,” said Prasad Gogineni, Distinguished Professor of Electrical Engineering and Computer Science. Gogineni serves as director of CReSIS, which was established at KU by the National Science Foundation in 2005.

Analysis of the radar images shows a vast majority of the ice layers are undisturbed, flowing smoothly from year to year for centuries, but the radar soundings occasionally return distorted images from deep within the ice. Ice core samples taken at NEEM reveal the distortion in the radar images corresponds to ice layers mixing, which occurs when temperatures rise.

“From the ice core studies, we learned that the ice that’s broken is from the warming during the Eemian period,” Dahl-Jensen said. “We also discovered ice crystals from this period are much larger (approximately 1 inch) than those present when it’s much cooler and the ice flows smoothly. Those ice crystals are less than (a tenth of an inch).”

As layers of snow accumulate year after year on the glacial surface, they pile up and compact, transforming to solid ice about 230 feet below the surface. Sealed within the ice throughout layers that date back thousands of years are miniscule air bubbles that provide a remarkably clear snapshot of the atmospheric conditions at the time of each year’s snowfall. Using this data, researchers can accurately gauge changes to the overall ice sheet.

“About 128,000 years ago (at the outset of the Eemian), the ice was about 650 feet higher than it is today. About 122,000 years (peak temperatures during the Eemian), the ice was about 425 feet lower than today,” a drop of nearly a quarter of a mile, Dahl-Jensen said. “That tells us there was about 6,000 years of intense heat.”

Elevation changes also reveal new information about Greenland’s impact on sea level rise during the Eemian period. The Greenland ice sheet saw an overall reduction of 5 to 10 percent, which Dahl-Jensen suspects would lead to about a 6 1/2-foot rise in the sea level.

“We know from other observations that during this period, sea levels were actually 20 to 30 feet higher than today. So this tells us indirectly that Antarctica must have contributed at least 16 to 23 feet of sea level rise. Smaller glaciers in total don’t have enough volume to account for more than 2 feet of sea level rise, so Antarctica appears to have a played a bigger role,” Dahl-Jensen said.

Nature was first published in 1869 and is one of the most cited interdisciplinary scientific journals in the world.

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