Measuring Greenland's Snowfall

Note: We were doing a little housekeeping and came on this update on the Arctic Circle Traverse written back in June. It holds up as a nice view into what it takes researchers to "collect data," so here you go. We hope to hear more from Box when he returns from Greenland after retrieving data from his time-lapse cameras observing the Petermann Glacier. Even the best planned plans can go awry. So it went in April and May, when a series of mishaps beyond their control kept the five-person team led by Jason Box from heading out to the field for their Arctic Circle Traverse (ACT), a National Science Foundation-supported study of snow accumulation on the Greenland Ice Sheet.

Snow storms, the eruption of the  Eyjafjallajökull Volcano in Iceland,which prevented airplane flying, and aircraft problems grounded the crew and originally dashed their hopes of getting out on the ice.

"Our biggest challenge was getting into the field," says Box. "We learned that the traverse, while labor-intensive, is more likely to succeed than depending on flights, especially in east Greenland."

Just when things were looking their grimmest, the team got a window of clear weather and set out for 13 days.

Sleeping under "turbulent" Aurora Borealis at night and blazing trails during the day, they successfully traversed roughly 700 kilometers. Over the journey, the team gathered the necessary information to map snowfall rates across the ice sheet, Box said.

They measured snow depth using radar, and took ice cores as well. Isotopes in the cores allow scientists to identify annual snow accumulation; radar and coring used in conjunction provide more specificity than either technique would alone.

As they traversed, a NASA P-3 airplane flew over their line and collected radar data that measured the layering structure of the snow, providing "virtual ice cores."

"It's nice to have the P-3 data, as it will cover a much larger area," says Box. However, the airborne radar doesn't replace actual ice cores, he says.

"So far there is no way to efficiently remotely sense the vertical profiles of density," says Box. "Cores remain necessary in-situ observational data."

The research aims to provide an accurate analysis of snowfall on the Greenland Ice Sheet. Box and his collaborators, Rick Forster (PI on a related NSF grant that seeks to fill holes in the snow accumulation data), Evan Burgess, and Clément Miège (University of Utah) are measuring annual snow fall to better understand how much of the ice sheet volume change and, in turn global sea level, is due to changes in snowfall or due to changing melt rates.

"We know that melt rates have increased in recent years," the group writes. "Yet, we also know that as climate warms, the atmosphere holds more moisture and consequently, more snow is delivered to the ice sheets. Our project will help better understand the effect on the mass budget of changing mass input from snow accumulation variations in the past 30-60 years. We're like auditors, with really thick parkas on."

Those parkas kept the crew warm as they worked and camped in temperatures as low as -35 C (-31 F) at night and up to -5 (23 F) to - 25 C (-13F) during the day.

Now that they're home, they've hung the parkas in the closet and begun the long task of analyzing the data, says Box.

"The core just made it off the ice sheet, and it needs to be put into the core melter to get the isotope and other chemistry data," he says. "A graduate student, Clement Miege, will spend much of the summer identifying layers in the ground radar data."

The team will present preliminary results at the AGU meeting in San Francisco this December.  —Rachel Walker