On 2 July we received the last satellite communication from a sea-ice buoy that had been released in the High Arctic two years earlier. The buoy had travelled nearly 6000 km and had left the Arctic Ocean through Nares Strait, a narrow waterway between Ellesmere Island and Greenland. It had travelled through Baffin Bay and finally stopped transmitting off the coast of Newfoundland at a latitude just 22 miles further north than Oban. It’s likely that transmissions came to an end because the ice that the buoy sat on melted, so that the buoy sank to the seabed, from where satellite transmissions remain impossible.
The buoy was one of five released to study the distribution of sea ice thickness in a little observed region north of Greenland as part of the EU-Framework 5 funded GreenICE project. While satellite images gather reliable figures concerning the extent of sea ice, much scientific controversy remains about remote measurements of ice thickness. It is, however, important to have reliable estimates for both sea ice extent and thickness to inform our understanding of the changes that are taking place in the Arctic Ocean.
The buoys were released in May 2004 from an sea-ice camp in the Arctic Ocean, and carried highly sensitive tiltmeters, which monitor the directional spectrum of flexural-gravity waves passing through the ice. These wave spectra have been proposed to be related to ice thickness, which – if correct – would allow for remote measurements of ice thickness. Data collected by the buoys was relayed back to the laboratory using the Iridium satellite system.
Two of the five buoys had taken the route out of the Arctic Ocean through Nares Strait, one stopped transmitting in January 2005 due to a battery malfunction. The remaining three buoys continue to transmit information to us from the Arctic Ocean. The five buoys had been put out on an array of locations around the ice camp as their routes demonstrate.
When the instruments were initially deployed the buoy data was validated by overflights from a Danish swath-sounding laser profilometer and a German helicopter with ice-sounding electromagnetics, as well as by drilling. Subsequently the buoys have continued to record twice daily spectra.
Work is ongoing on the final assessment of the validity of the relationship between tilt and ice thickness.
Seven other buoys have been deployed earlier this year around the mouth of Nares Strait on sea ice and icebergs to further study ejection of ice through this important channel. These are currently stuck in place, but the likely break-up of the ice bridge during the summer may produce more detailed information of ejection pathways and rates.