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Spit of land seen between ice.
Photo Credit: J. Severinghaus
Thrust faults near the bed of Taylor Glacier, the sort of thing might be found by RAID near the bedrock below the ice sheet. The thrust faults are the dark inclined bands that bring dirt from the bed of the glacier up into the clean ice. They start out as folds but become overturned and stretched, and start sliding along the dirt band because the dirt softens the ice. For scale, the total ice cliff height is 50 meters.

New drill will serve as reconnaissance tool for glaciologists

The oldest ice core recovered to date is about 800,000 years old, coming from the European Program for Ice Coring in Antarctica (EPICA) External Non-U.S. government site at Dome C, a rise in the East Antarctic Ice Sheet more than 3,000 meters above sea level.

“The main challenges are finding the ice, because it is likely to be in a limited area where fortuitous circumstances have allowed its preservation,” Severinghaus said. “So, a low-cost, rapid reconnaissance type of drilling is needed, unlike the five years typical of the time it takes to recover an ice core. This way we can rapidly scan for potential targets.”

Map of Antarctica.
Graphic courtesy: John Goodge and Eric Rignot
A map of Antarctica shows the target area for RAID in East Antarctica.

Severinghaus knows what is involved in such a field campaign. He was one of the PIs on the West Antarctic Ice Sheet (WAIS) Divide External Non-U.S. government site program, a project that recovered the longest ice core in U.S. history over the course of five summer seasons. The climate record from WAIS Divide is expected to reach back only about 68,000 years but at unprecedented detail. [See previous article — The last core: WAIS Divide deepens borehole for research into climate change.]

“The International Partnerships in Ice Core Sciences (IPICS) External Non-U.S. government site is already planning to drill this core [of million-plus-year-old ice] sometime in the next decade, but they haven't located the site yet,” Severinghaus said. “That’s our job.”

The RAID team will rely on existing geophysical data – such as ice-penetrating radar imagery of the ice stratigraphy and bedrock topography from instruments flown aboard airplanes – to pinpoint potential targets across a wide swath of East Antarctica. Goodge said he hopes there will be additional airborne campaigns to collect even more information in the next couple of years.

In particular, instruments that measure rock properties such as magnetism will provide a way to map the landscape below the ice to ensure the team hits different targets of interest with the drill.
“Over time, we can range over a pretty wide area,” Goodge said.

An obvious site for the geologists is the Gamburtsev Mountains, a mountain range the size of the European Alps, but buried below the ice sheet. However, previous research in the region found that the ice near the bedrock may be freezing and refreezing, likely limiting its potential for old ice. [See previous article — Frozen at the bottom: AGAP scientists turn understanding of ice sheet dynamics upside down.]

Radar image overlain with arrows and text.
Graphic courtesy: John Goodge (radar image from Duncan Young)
The above images illustrates the different objectives of RAID superimposed on a cross-section of the Antarctic ice sheet provided by ice-­penetrating radar, which shows the detailed internal structure of glacial ice.

Any attempt to interpret the climate record from the bottom of an ice sheet that far back in time will be tricky, Severinghaus conceded.

“It is really a research topic that is just now being explored,” he said. “For example, studies have recently been published on how fast diffusion in the ice will erase the signals of temperature and CO2 concentration in ice near the melting point and at high pressure.”

Still, there is reason for optimism, he said. CO2 concentrations are still recoverable from the 41,000-year cycles if captured in ice at least about four meters thick. Temperature records at those timescales are harder to identify but still possible using different techniques.

The project is not all about rock and ice, according to Goodge. There is also great interest in understanding the boundary conditions between the two. For example, how much heat is emanating from the earth into the ice? Is there water? Is the ice frozen directly on the bedrock? Is it thawing and refreezing?

“We don’t know what’s going on in East Antarctica. That boundary zone and the nature of its properties are also important,” he said.

The project will also bring aboard biologists to determine if life existed – or still exists – in that zone between the ice and rock. Researchers in other parts of Antarctica have found microbial life eking out an existence in other extreme environments, from a subglacial lake to a hyper-saline pool under a glacier, and even inside the outer layers of rocks.

“There are lots of different things going on,” Goodge said.

NSF-funded research in this article: John Goodge, University of Minnesota Duluth, Award Nos. 1419935 and 1242027 External U.S. government site; and Jeffrey Severinghaus, University of California-San Diego Scripps Institution of Oceanography, Award Nos. 1419979 and 1242049 External U.S. government site.