Brussels, 25 July 2002
The European space agency (ESA) ocean/ice unit has been tracking the movements of an unusually heavy Antarctic sea ice pack that has trapped ships attempting to deliver supplies to scientific bases.
Polar supply vessel Magdalena Oldendorff has been ice-bound for more than a month after becoming trapped by ice on its return from a Russian base. A few months ago, British ship RRS Ernest Shackleton was blocked from its own supply mission to remote ice shelf Halley by unprecedented sea ice conditions during the Antarctic summer.
Shackleton is an ice-strengthened vessel, but pack ice in the eastern Weddell Sea was so unusually heavy this summer that it was unable to penetrate through to Halley,' explained ESA's Mark Drinkwater. 'What's significant is that this was the first time in Halley's 44-year history that this has happened.'
Data from ESA's ocean/ice unit has revealed that pack ice, which normally melts each summer, was thicker and more resilient this year. Although such observations are normally blocked by darkness and cloud cover, microwave radar-based instruments like those on board ESA's ERS-2 and the Envisat spacecraft can see where photographic light cameras cannot. The instruments work by beaming radar waves onto the surface of the ice and then recording how it is scattered back towards the spacecraft.
ESA is interested in monitoring sea ice because it has important implications for the climate and climate change. Ice is a good insulator, and prevents the exchange of heat between the relatively warm ocean and the cool atmosphere. The process of seawater freezing also helps to drive ocean circulation.
The agency's sea ice monitoring programme is due to receive a significant boost with the launch of Cryosat, an Earth explorer opportunity mission set for launch in April 2004. Specifically designed and built for Earth observation, Cryosat will help carry out routine monitoring of ice conditions by recording ice thickness and topography.