Getting to the bottom
NICL team processes deepest ice from WAIS Divide project
Posted September 2, 2011
Mick Sternberg had literally made the same measurement a thousand times before. But this meter-long ice core was perhaps just a little more special. He double-checked his numbers on the final length, stood back, and rechecked again.
“No reason to rush through this,” he said under his breath, which steamed out in the freezing temperatures of the National Ice Core Laboratory’s processing room.
After all, this last section of ice, drilled from near the bottom of the West Antarctic Ice Sheet (WAIS) at a depth of about 3,331 meters, had been waiting around for a while. Probably somewhere in the neighborhood of 55,000 to 60,000 years.
Sternberg, an intern at the National Ice Core Lab (NICL), gave a nod and the cylinder of ice moved down the ice-core processing line shortly after 3 p.m. on Aug. 16. It would be trimmed, scanned, sliced and diced to be sent out with tons more ice to laboratories around the United States for various analyses.
“It’s really cool to be here at the end of this,” said Ed Brook , one of the principal investigators on the WAIS Divide project whose lab at Oregon State University is one of several analyzing the trapped gases in the ice core, particularly those associated with the greenhouse effect, like carbon dioxide and methane.
“I’m pretty confident that that the data are going to be as good as we said they would be, just looking at the ice and its quality, and as good as the processing has been,” he added.
The cores had been extracted from a high, snowy spot in West Antarctica where ice begins to flow in different directions, akin to the Continental Divide in the United States. The location would help guarantee a simple stratigraphy, with thick layers that represent individual snowfall years that went deep into the ice sheet. Researchers believed they would be able to construct a climate record from the ice so good that they could count the individual years for at least 40 millennia.
“The quality of the ice is better than we expected. The age of the ice is younger than we expected, but for most of what we’re doing, that’s a good thing, because it gives us a higher time resolution for our record,” explained Kendrick Taylor , chief scientist of the WAIS Divide project, who was at NICL a few weeks earlier.
The project reached its target depth in West Antarctica on Jan. 28 after five years of drilling, representing the deepest core ever drilled by the U.S. ice-coring community. [See related article: Deep core complete.] Researchers had expected to recover ice as old as 100,000 years, but preliminary indications from the ice-core processing line (CPL) at NICL are that it is maybe 60,000 years old at the bottom.
“We’re trading off the amount of time covered by the record for a record with more detail. To some extent, it’s disappointing that we’re not going to get the last interglacial period,” Brook said, referring to a warmer time more than 100,000 years ago between ice ages, though it was unlikely the record would have gone back that far in time. The present time, called the Holocene, is also an interglacial period.
“Instead, we’re going to get a lot more information about younger times. It’s actually a good fit for what’s needed to understand Antarctic climate. It’s going to be a more unique record than if it was longer,” he said.
Topping the science goals is the reconstruction of carbon dioxide concentrations in the atmosphere over the timeline represented by the WAIS Divide core at a resolution never before achieved.
CO2 is one of the primary greenhouse gases that most researchers believe is causing the planet to warm and the climate to change. They are particularly interested in determining whether natural increases and decreases in CO2 in the past preceded or followed temperature changes. That would help scientists better understand the relationship between temperature and CO2 today.
Other ice cores have shown that CO2 lags temperature, but there is uncertainty about the timing because the age of the ice is different from the age of the trapped gases, sometimes on the scale of centuries or millennia. The WAIS Divide core should be able to constrain much of that uncertainty because the annual layering offers such a highly detailed view of the past.
“I feel very confident saying this is really the best place on the planet to figure how greenhouse gases influence the climate on the timescale of the last 50,000 years or so,” said Taylor, a research professor at the Desert Research Institute in Nevada.1 2 Next