Shortly before Jakobshavn Isbræ, a tidewater glacier in Greenland, calves massive chunks of ice into the ocean, there’s a sudden change in the slushy collection of icebergs floating along the glacier’s terminus, according to a new CIRES-led paper. The work, published today in Nature Geoscience, shows that a relaxation in the thick aggregate of icebergs floating at the glacier-ocean boundary occurs up to an hour before calving events. This finding may help scientists better understand future sea-level rise scenarios and could also help them predict when major episodes of calving are about to occur.
In winter months, icebergs and sea ice accumulate within the fjord in front of Jakobshavn Isbræ, forming a frozen plug that prevents calving. The glacier can continue to flow into the fjord, intact, and advance dozens of meters each day. This accumulation of icy material, which scientists refer to as ice mélange, persists into the summer, but its shelf-like structure loses rigidity in the relative warmth, and it behaves more like individual icebergs jammed together in the fjord. Until now, no study has shown whether this type of late summer ice mélange can influence iceberg calving.
“It only takes a small bit of strain for the mélange to stretch or relax a little bit, and so it’s no longer an ice jam,” said Ryan Cassotto, a researcher in CIRES’ Earth Science and Observation Center and lead author of the new study.
Read more at: University of Colorado at Boulder
Scientists work on time-lapse cameras at the edge of Jakobshavn Isbræ in Greenland. The instrument on the right is one of ground-based radar interferometers used to record the movement of icebergs within the proglacial fjord. (Photo Credit: Ryan Cassotto/CIRES)