Page 2/3 - Posted August 20, 2010
Slicing and dicing
At the front of the CPL, where the core handlers are using lasers to measure the length of each section of core before the cutting and examinations begin, precision is of utmost importance.
“This is probably the most critical part for us right now — making sure we get a good length. This is what’s going to give us the true depth of the ice we’re hauling up out of the hole,” explained Geoffrey Hargreaves, NICL curator since 1993.
Together with the electrical conductivity measurements, the length measurements provide an age-to-depth relationship, which is important for the subsequent analyses involving chemistry, isotopes and gases, according to Hargreaves.
“Without good age, without good depth control, you’ve got nothing,” he said.
Then the ice is ready for various dissections. Top sections are cut into different slabs that are ripped and chopped into smaller pieces depending on what they’ll be used to measure. For example, 3-centimeter-square sticks of ice will be used for different chemical measurements covering 70 percent of the elements in the periodic table.
The chemistry can reveal information about past conditions such as sea ice extent, the amount of dust in the atmosphere and even seasonal changes, which reveals clues to the environmental conditions of the time.
The other half of the core then undergoes the electrical conductivity measurement before a camera creates a high-resolution scan. Spencer then makes his visual inspection before pushing the core farther down the line where some of the best sections are removed for later gas analysis, particularly carbon dioxide, methane and nitrous oxide.
“The gas guys get the best ice,” Hargreaves noted.
Currently, the CPL chews through about 35 meters of ice in a day. The best day so far was 39 meters. “That’s when everything is working,” Spencer said.
Photo Credit: Peter Rejcek
Bagged sections of the ice core await to be returned to the freezer warehouse archive.
At each step along the way the team members log the core sections before they disappear into plastic casings and insulated boxes destined for individual labs across the country. About a third or more of each core section will remain untouched, returned to its tube and the deep-freeze warehouse. The CPL database will eventually be merged into the NICL database to ensure the inventory in the freezer is up to date.
“I know exactly what’s in the tube sitting on the shelf. It makes it a lot easier to come back when somebody is looking for ice,” Hargreaves said.
The archive at NICL includes ice that was retrieved in 1958 at the Little America V station during the International Geophysical Year , when the modern era in polar science began. The oldest ice dates from the Vostok core, some 400,000 years.
As technologies change and improve, scientists still request samples from ice that’s been in the collection for decades.
“We resample cores from 15 to 20 years ago all the time,” Taylor said.
From beginning to end
The WAIS Divide project is the first ice-coring venture in which NICL staff has been involved from when the ice first emerges from the borehole in Antarctica to when it enters the CPL sawmill.
“It makes sense that we who handle the ice in the end should be there in the beginning to make sure it starts in the right way,” Hargreaves said.
Spruce Schoenenmann has experienced both the cold of the freezer room at WAIS Divide and at NICL as a science technician responsible for handling the core. And he’ll see some of the same ice a third time when he finally melts it for analysis in the lab at the University of Washington, where he is a PhD student under WAIS Divide principal investigator (PI) Eric Steig .
“I will see it all the way through from start to finish,” Schoenenmann said.
Taylor noted that many of the graduate students at NICL will handle the ice multiple times before it is melted and the water sucked into a spectrometer or other instrument for analysis. Many have their PhDs riding on the results.
“That’s great because they have a very vested interest in making sure [the CPL is] done right,” Taylor said.
Most of the technicians who head south to Antarctica are hired for the project because they are involved directly in the research or plan to continue their education in a related field, according to Mark Twickler, manager of the WAIS Divide Science Coordination Office (SCO). The WAIS Divide SCO, based at the University of New Hampshire , manages the day-to-day operations of the project.
“It’s interesting; a lot of the PIs now that are working on the ice core were graduate students during the GISP-2 days,” said Twickler, referring to an ice core project in Greenland during the 1990s.
“It was a great training experience for the students. The same thing is true today with the students coming to NICL and the science techs going down. We’re still trying to get people field experience and ice-processing experience,” he added.
Photo Credit: Tommy Cox/WAIS Divide
Bess Koffman prepares a snowpit speciment for a density measurement at WAIS Divide during the 2009-10 field season.
The Greenland ice core project is partly responsible for Bess Koffman becoming a polar scientist.
During her junior year at college, she heard a lecture by the well-known glaciologist Richard Alley of Penn State University about the discoveries from the GISP-2 core. She read his book on the subject, The Two-Mile Time Machine, and two years later she was on the Ice working as a field technician at the U.S. Antarctic Program’s Palmer Station.
Now a PhD student at the University of Maine , Koffman sees the experience of doing the grunt work involved in ice-core drilling and handling, in both Antarctica and at NICL, as an important lesson on the path of her academic career.
“The ability to participate in every step of the process has allowed me to see my PhD research in the context of the whole. I really feel part of the overall WAIS Divide community,” said Koffman, who is busy back at her lab melting water from the upper meters of the core for analysis. She worked at the WAIS Divide field camp in 2008-09 and 2009-10.
Her research focuses on the role of atmospheric dust in the climate system that can be found in the ice. She is particularly interested in understanding how dust controls iron geochemistry in the ocean. Iron is an important but limited nutrient for phytoplankton growth in the Southern Ocean.