Antarctica’s wandering ice shelf
GPS markers usually pinpoint a spot on the earth’s surface to help everything from map-making to navigation.
This one (left) spectacularly didn’t.
In fact, it wandered hundreds of miles (km) this year on an iceberg, blown by winds or carried by ocean currents in huge pirouettes off the coast of Antarctica.
When glaciologist David Vaughan (above) of the British Antarctic Survey stuck the pole holding the GPS (global positioning system) tracking device into the Wilkins Ice Shelf in Antarctica in January, the ice felt solid as rock.
Stuart McDill of Reuters TV and I had landed with him in a small plane mounted with skis on a 40-km-long floating ice bridge which had been in place probably for thousands and thousands of years. But it was weakening and about to snap in what Vaughan said was a sign of global warming.
We didn’t stay long.
The GPS marker was meant to transmit its position to satellites to help monitor movements in the ice shelf — up to about 250 metres thick — to measure the strains before it finally cracked up. The ice bridge shattered in April and collapsed into a swarm of icebergs.
But surprisingly, the GPS kept on going for months — broadcasting its position as a lone metal spike that may have puzzled passing penguins or the odd whale. The diagram above shows where it began (near top right by Charcot Island and then southwest until its last transmission on Aug. 30. No one knows its fate – maybe the batteries gave out or its iceberg cracked up.
The GPS did far better than planned. Vaughan had been convinced that the GPS, set up for Michiel van den Broeke of Utrecht University and colleagues, was not going to work at all. After he set it up, it went “beep beep beep” to signal that it was OK but then fell silent.
We all thought it had failed; we didn’t know that it was programmed to beep only briefly to show that it worked — too many beeps would have drained the batteries.
(Picture: REUTERS/Alister Doyle, diagram: Roderik van de Wal, Utrecht University, Matthias Braun, Bonn University)