SOMETIME this Antarctic summer, will fly to the mouth of Pine Island glacier in West Antarctica. It’s a dangerous place. “You get these monster crevasses,” he says. “If your helicopter needed to set down, it’s not a trivial matter.”
But glaciologists like Anandakrishnan need to take such risks to predict how much of the Antarctic ice sheet will end up in the ocean due to climate change. So he is developing “geoPebbles” – wireless, instrument-laden devices that can be scattered from a helicopter hovering a few metres above the ice. They are one of a host of new polar exploration technologies now helping to monitor Earth’s frozen frontiers.
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“Instrument-laden devices can be scattered from a helicopter hovering a few metres above the ice”
Pine Island glacier is ground zero for climate change in Antarctica. Warm ocean waters are melting the underside of the ice shelf that fronts the glacier, causing its descent into the ocean to accelerate. Key to figuring out a glacier’s response to such melting is to know the conditions at its base. “We are really kind of in the dark about what’s underneath there,” says field glaciologist of the University of Colorado in Boulder.
Satellites can see the surface of the glacier and measure its thickness, but cannot tell what is happening at the base. So glaciologists use devices called geophones which record vibrations on the ice surface. They then set off small explosions and the reflected sound waves are recorded by the geophones, revealing the nature of the material below the ice, be it water, sediment or bedrock.
GeoPebbles will soon let Anandakrishnan and his team at Pennsyvania State University in University Park do this in dangerous, crevassed areas of glaciers. They presented the design at a meeting of the . Each pebble is a box 15 centimetres to a side and contains a GPS, three geophones, a battery and Wi-Fi. The entire sealed unit is rugged enough to survive a 3-metre drop. The idea is to scatter these geoPebbles on the glacier surface and then set off small explosions. The geoPebbles will monitor the reflected sound waves and wirelessly transmit their data to a base station. Anandakrishnan will be testing a prototype in the coming weeks.
Near the other pole, Greenland’s glaciers are breaking up and retreating at alarming rates. Warm Arctic summers can melt the surface of glaciers, and the meltwater flows down vertical shafts called moulins to the bottom of glaciers. A key question is whether this meltwater is acting as a lubricant, causing the glaciers to slide faster into the ocean.
Glaciologists have drilled down to the bottom of glaciers in Greenland to check the water pressure there. High pressure means the water is flowing through many small drainage channels, and this helps speed up a glacier. Low water pressure indicates the formation of a few big drainage channels. This slows down the glacier. But drilling boreholes is laborious and provides insufficient information.
So at the University of Bristol, UK, and colleagues have developed dubbed “cryo-eggs” that can simply be dropped into moulins. These sensors are packaged in watertight plastic spheres about 5 centimetres across and wirelessly transmit the sensed water pressure, which is received by an antenna on the surface. In August, Bagshaw (pictured) and colleagues dropped 23 such spheres into a moulin on the Leverett glacier in Greenland, and recorded water pressure from 17 spheres from a listening station 1.6 kilometres away. The spheres transmitted signals through hundreds of metres of ice. One sphere even made it through the glacier’s drainage channel and popped out at the mouth.
The team is developing a more robust cryo-egg, a 12-centimetre sphere made of tough thermoplastic, with greater battery power for a more powerful radio transmitter. “We’d like to deploy these larger cryo-egg sensors under much thicker ice, for example, in Antarctica,” says Bagshaw.
There are other pressing concerns in the Arctic when it comes to climate change. The Arctic sea ice is melting faster than climate models predict. One region that influences this process is the marginal ice zone (MIZ), the boundary between the open and frozen oceans. “It’s important to understand the physics behind what forms the MIZ, how energy is transmitted within it, and how that impacts the break-up of the sea ice,” says at the University of Washington in Seattle. Easier said than done.
Lee and colleagues have developed an that roves under the ice, outfitted with various sensors to study the conditions. The 2-metre-long cylindrical hull has an external bladder that can be pumped with oil to increase the overall volume, boosting buoyancy, or deflated, causing the vessel to sink. Inside, small electric motors move the heavy battery from fore to aft, and from side to side. This allows the glider to move forwards as it sinks or rises, and to turn. The glider is now being used to survey the underside of the Ross ice shelf in Antarctica.
Yet another polar concern, back in the Arctic again, is methane that is burping out of thawing permafrost. Understanding the source of this powerful greenhouse gas is key to predicting just how much of it will end up in the atmosphere. A team from NASA has built a rover that can crawl on the underside of ice in the frozen lakes in Alaska (see “Upside-down explorer“). The aim is to equip the rover with tools to sample the methane seeps.
of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, says we need such autonomous polar exploration technologies. “Ultimately, it’s about having information that can tell us how to prepare for the future.”
Upside-down explorer
A rover that today explores the underside of frozen lakes in Alaska might one day do the same on icy moons in our solar system – not to study climate change, but to find signs of alien life. “One thing we know about life on Earth is that everywhere we have liquid water, we find life, pretty much without exception,” says Dan Berisford of NASA’s Jet Propulsion Laboratory in Pasadena, California.
Berisford and his team have built a buoyant rover that, when dropped into an ice-covered lake, floats up and sticks to the ice from below (see photo). Its cog-like wheels than crunch their way along the ice. The tethered rover transmits data from its cameras to a base station, which broadcasts the signal wirelessly to a researcher wearing video goggles who can see what the rover is seeing in real-time and steer it accordingly. The team tested the rover in Barrow, Alaska, home to more than 10,000 shallow permafrost lakes.
It is the first step towards designing something that could one day be sent to icy moons like Jupiter’s Enceladus, says Berisford. “If there was a place to look for life in a system like that, the ice-water interface will probably be the most interesting place to start,” he says.
