Down to a quadrillionThe Antarctic continent is far from being one huge, homogenous ice cube. ITASE scientists have found from their first series of traverses from 1999 to 2003 across West Antarctica great variability in snow accumulation rates as well as some of the reasons behind that variance.
They determined precipitation in the interior of the continent is relatively stable but also identified some regions of the Antarctic that may be on the verge of dramatic change.
“It’s an immense place, and there’s a lot of variability. It’s so dynamic it may not be that easy to tell how much it’s going to change,” said Mayewski, the principal investigator of the 13-person team that traveled on sleds and farm tractors – two Caterpillar Challenger 55s – across 460 kilometers of snow and ice.
“This place is potentially a bellwether for what’s happening in the whole planet,” he added.
The group started the scientific traverse on Dec. 13 from Taylor Dome, an elliptical ice ridge that rises about 2,400 meters above sea level. Its equipment had been left at Taylor Dome following a logistics traverse from the South Pole during the 2003-04 austral summer season.
Dan Dixon, an ITASE veteran, also participated in the South Pole to Taylor Dome journey, collecting ice cores from East Antarctica along the 2,500-kilometer route. A doctoral student from the Climate Change Institute, Dixon researches past Antarctic climate using ice core chemistry.
Lab analysis of the cores has revealed the start of anthropogenically introduced chemicals such as lead, although increased levels of pollutants such as nitrate and sulfate, which are very high in the Northern Hemisphere, are not yet rising over Antarctica. Advances in lab analysis allow Dixon and others to make chemical measurements of the atmosphere in the ice cores down to one part per quadrillion.
“We’re almost down to atoms,” Dixon said.
Down to the bedrockThe team also uses several different types of radars for its work on the ice sheet. One is ground-penetrating radar that looks at the upper 15 meters of ice. It is used primarily for operations – snooping out crevasses. The radar is attached to a 10-meter-longboom in front of a PistenBully that rides at the head of the heavy traverse train.
“This is a critical piece of safety equipment for the team as crevasses, cracks in the ice, can be so large here that the trains could literally be swallowed up,” wrote Lora Koenig on the team’s online journal while it was at Taylor Dome preparing for the traverse.
Koenig, a doctoral student at the University of Washington, is interested in how space-borne satellites monitor snow properties over ice sheets. During the traverse, she also used high-frequency radar to penetrate the top meter of snow to image grain size, stratigraphy and thermal conductivity. She will compare those measurements to models of microwave remote sensing data of the ice sheet to determine the accuracy of the latter.
Another radar penetrates about 100 meters, the same depth of the deepest cores the team took this season. Finally, deep-penetrating radar can see down thousands of meters to the sub-glacial bedrock. The radar operated continuously and picked out details of the bedrock the scientists had not seen before, as well as the existence of a couple of small, sub-glacial lakes.
“We’re interested in understanding, from this radar, the ice dynamics,” Mayewski said. Based on data from previous ice cores, the team can use the radars to find certain reflectors in the ice that it can date to a certain time period. The scientists then calculate the changes in snow accumulation while dragging the radar along the traverse route.
Brian Welch from St. Olaf College in Minnesota operated the deep radar system, which trailed behind on a separate sled at the end of one of the two tractor trains. The instrument can detect whether water sits between the top of the bedrock and the bottom of the ice sheet. That’s important for understanding ice flow: the ice moves faster if it’s not frozen to the bedrock.
“At Byrd Glacier, the bedrock is really, really bright,” said Welch, who accompanied the ITASE team on three previous traverses of West Antarctica. “That means there’s water down there. If there’s water there, the ice can start flowing much faster.
“[East Antarctica] looks a lot more like what you would expect if you were doing seismology in sand dune areas than what you would expect to see in East Antarctica,” he added. “East Antarctica is a much more dynamic place than we thought it was.”