Visiting researchers use Geosciences lab to analyze sediment cores

June 20, 2013
Taking advantage of UMass Amherst’s investment in cutting-edge analytical equipment for geosciences research, several visiting geologists who collected the first subglacial sediment cores ever extracted from a lake deep below the west Antarctic ice sheet recently spent three days at the campus’s Hartshorn Quaternary Lab using two rare, state-of-the-art machines to analyze their hard-won samples.
Julie Brigham-Grette, associate department head in Geosciences, says UMass Amherst is one of only a handful of institutions in the United States with a Geotek machine that provides high-resolution, non-destructive physical (density, mineral content), magnetic and chemical (photometric) analysis of sediment cores. Further, the Hartshorn Lab has an even more rare apparatus, the ITRAX core scanner housed in the X-ray Fluorescence Laboratory. It uses X-rays to identify element profiles in split-core sections up to 12 cm (4.7 inches) in diameter and 1.8 m (about 6 feet) long. There are only two or three others in the country, Brigham-Grette notes.
“We are the go-to place to do this kind of work,” she says. “These cores are unique and extremely valuable, and they’re also quite vulnerable to damage once you open them. You don’t want to have to move an opened core around to different labs to use different instruments. So the one-stop shopping we offer here is important.”
Both Ross Powell and Reed Scherer, geologists at Northern Illinois University (NIU) and leaders of the visiting Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) team that opened the Antarctic ice cores here for the first time this month, agree. “You have a world-class facility here, especially the scanning instrument, which is so valuable to us. Plus, you have very capable and nice people who know how to use it properly,” Scherer says.
UMass Amherst bills visiting researchers for each run of the machines to help offset the costs of investing in such specialized equipment.
The WISSARD team’s work, supported by the National Science Foundation (NSF), will help scientists piece together a picture of past climate on the Antarctic continent, where ice sheets are known to have retreated at least once, and perhaps more often. Scherer says he and his colleagues will try to determine the age of sediments and microfossils detected in their core samples as evidence for when the west Antarctic ice sheet last retreated and how many times this may have occurred. This exploration of past environmental conditions may also help to determine how likely a future retreat might be.
Other members of the WISSARD research team are Scherer’s co-leader, professor Ross Powell, with geology doctoral student Tim Hodson of NIU; Slawek Tulaczyk, professor of earth science at the University of California, Santa Cruz, and environmental studies researcher Stefanie Brachfeld of Montclair State University, New Jersey. They were in Amherst from June 10 to 13 overseeing the first analyses of cores they collected between November 2012 and February 2013, Antarctic summer, from subglacial Lake Whillans.
The team used a three-inch-diameter hose mounted on a huge crane that delivered hot filtered water and steam to bore a hole through 2,600 feet of ice to reach the lake. Employing three different coring methods, they obtained a total of about 3 meters (10 feet) of sediment samples. One method samples about one-half meter of material at the interface between bedrock and the ice sheet above it. The scientists hope data from this zone will help answer one of the major geoscience questions of recent decades: Whether the ice sheet is frozen solid to bedrock or whether it is “floating” on a layer of slushy mud and liquid water. The answer should offer a clue as to how easily the ice sheet can be dislodged as forces related to climate change, for example, begin to take effect.
A second method called the piston-core is designed to sample the sediments at medium depths up to about 2 meters (6.5 feet) and the third, called a percussion core, penetrates the deepest into sediments, up to 5 meters. They accomplished all this with “clean access,” says Scherer, that is without contaminating the lakes with bacteria or other microorganisms from the surface. “It’s like visiting another planet. You don’t want to introduce any foreign material into this pristine environment. Not only because it might cause damage, but also because it could compromise our investigation, one part of which is to find what kind of microbial life thrives in these lakes today.” 
Powell and Brigham-Grette are part of a team that have co-led the NSF’s Research Experience for Undergraduates program on tidewater glaciers and lakes on Spitsbergen in the Svalbard archipelago of Norway for the past 10 years.
Photo: Visiting geoscientist Ross Powell, left, and Reed Scherer, right, of Northern Illinois University, with Geosciences graduate student Jeremy Wei, center, position one of their Antarctic subglacial lake sediment cores in preparation for cutting. Half of each core is used for research and half will be catalogued at the Antarctic Marine Geology Research Repository at Florida State University.