[youtube=http://www.youtube.com/watch?v=U9UAuoL1Dv8] Before Dr. Alberto Behar of the NASA Jet Propulsion Laboratory tossed an enclosed camera into the gaping hole that bored into Jakobshavn Glacier last summer, he took a moment to listen to the roar of the river plunging into the ice.
"It sounds like a jet engine," said Behar last week from the American Geophysical Union annual meeting in San Francisco. "If you fall in there, forget about it. You're not going home."
While a human would be hard pressed to survive a "dip" in a moulin—a narrow, tubular shaft in a glacier that guides water from the surface to the glacial base—Behar and co-investigator Dr. Konrad Steffen of the University of Colorado, Boulder, are hoping to design a high-tech, video and camera-equipped probe that will. Specifically, they recently completed the fourth field season of a NASA-funded study on moulins.
Their team is developing a tool to measure the depth of moulins and, ideally, track the path of water from the surface to the ocean. The best-case scenario would be if one of the probes dropped into a moulin emerged later in the ocean and "could tell us where it had been," said Behar in the press conference.
Behar and Steffan call their tools "expendable rovers." The size of a pocket book, these solar-powered systems are modeled after the Antarctic Ice Borehole Probe, which studied ice streams in West Antarctica, the Amery ice shelf in East Antarctica and the Rutford ice stream in West Antarctica.
The Greenland version is modified specifically to explore the moulin environment. It consists of two high-resolution charge-coupled device cameras (a side-viewing digital camera and a downward-viewing video camera), lights, associated electronics and an inclinometer that measures the tilt of the moulin chute.
Images are sent in real time through a tether one kilometer long (about 3,300 feet) to a receiving station at the surface. The station has a video display, computer and digital tape recording devices.
Earlier this year, working in bitter cold, slushy, windy conditions (minus 10 degrees Celsius, or 14 degrees Fahrenheit), the scientists deployed the probe in two locations of a moulin. Once the probe descended to 110 meters (361 feet), it encountered horizontally flowing water and debris about one to two meters (3.3 to 6.6 feet) deep.
In this particular moulin, the water flows out in well-developed channels to the edge of the ice sheet. At the time of the experiment, the scientists measured the water flow rate of the surface melt rivers feeding the moulin at approximately 15 cubic meters a second (about 238,000 gallons a minute).
"This was very interesting and is evidence that we need an integrative plan on how to study these in a more sustainable way," said Behar. "We need to get multi-year funding."
Behar and Stefan have been developing a moulin probe since 2006, and Behar offered the following synopsis for each year of field work in the Pakisoq region.
- 2006 The team used an ice borehole camera that shot an image about 100 meters down a Moulin. However, the camera was heavy and proved to be difficult to work with.
- 2007 The team returned with a Sony HD video recording camera in a watertight Lexan enclosure. They sent the camera into the Moulin, but the images were hard to interpret. "It was a lot like fishing," said Behar. "We found the crevasses are much more complex than we had thought."
- 2008 The team developed a simple device with a tracker GPS modem that had temperature sensors and could measure the pressure. They expected it to follow the water pathway, emerge and call home. They never heard from it again.
- 2009 The team developed a live video feed camera system with a fiber optic cable. The camera transmitted images to special glasses (Behar calls them "Blade Runner-esque"), and the viewer could watch the camera's progress.
"This was an exciting, important first look into a place that's not well understood but could have an important role in understanding the dynamics of this region," said Behar. "We're excited by the possibilities this technology holds, not only for future studies of Earth's icy regions, but also for future missions to explore extreme ice and liquid environments on other planets, such as the Martian polar ice caps and Jupiter's moon Europa."
Next year, University of Colorado scientists will use ground-penetrating radar to accurately measure the glacial ice thickness at this location. These data will help scientists better interpret their findings and plan future tests.
Scientists expect moulins to shed light on complex glacial dynamics, which are not well understood and are responding rapidly to climate change. Previous NASA measurements in the Pakisoq region using global positioning system data show the ice there moves an average of about 20 centimeters (8 inches) a day, accelerating to about 35 centimeters (14 inches) a day during the summer melt. Scientists suspect the moulins may affect—directly or indirectly—that rate of advance.
In Greenland, the surface of the ice sheet moves at varying speeds, on both seasonal and shorter-term time scales. Seasonally, glacial water penetrates to the glacier bed through significant thicknesses of cold ice. However, early in the melt season and at other times, there can be periods when water flows rapidly into glacial drainage systems, resulting in sudden new flows of water out of the glaciers. In the middle of the melt season, surface melting resumes after periods of cold weather, which can partially close sub-glacial channels.