Runaway Antarctic Ice Loss In The Cards; Warm-water Channel Carving Deep Into Ice Sheet
Abstract
Ice shelves play a vital role in regulating loss of grounded ice and in supplying freshwater to coastal seas. However, melt variability within ice shelves is poorly constrained and may be instrumental in driving ice shelf imbalance and collapse. High-resolution altimetry measurements from 2010 to 2016 show that Dotson Ice Shelf (DIS), West Antarctica, thins in response to basal melting focused along a single 5 km-wide and 60 km-long channel extending from the ice shelf's grounding zone to its calving front. If focused thinning continues at present rates, the channel will melt through, and the ice shelf collapse, within 40–50 years, almost two centuries before collapse is projected from the average thinning rate. Our findings provide evidence of basal melt-driven sub-ice shelf channel formation and its potential for accelerating the weakening of ice shelves.
Plain Language Summary
Ice shelves act as safety bands around the Antarctic ice sheet. Many ice shelves are currently thinning, leading to acceleration of the grounded ice behind. Here we show that ice shelves' thinning is stronger along a channel structure formed by the ocean circulation under the ice shelf. The thinning is 3 times higher than the ice shelf's average, hence leading to a more rapid weakening of the ice shelf. This study provides evidence of basal melt-driven sub-ice shelf channel formation and its potential for accelerating the weakening of ice shelves.
EDIT
http://onlinelibrary.wiley.com/doi/10.1002/2017GL074929/abstract
Researchers from the University of Cambridge, the British Antarctic Survey and Stockholm University imaged the seafloor of Pine Island Bay, in West Antarctica. They found that, as seas warmed at the end of the last ice age, Pine Island Glacier retreated to a point where its grounding line - the point where it enters the ocean and starts to float - was perched precariously at the end of a slope.
Break up of a floating 'ice shelf' in front of the glacier left tall ice 'cliffs' at its edge. The height of these cliffs made them unstable, triggering the release of thousands of icebergs into Pine Island Bay, and causing the glacier to retreat rapidly until its grounding line reached a restabilising point in shallower water.
Today, as warming waters caused by climate change flow underneath the floating ice shelves in Pine Island Bay, the Antarctic Ice Sheet is once again at risk of losing mass from rapidly retreating glaciers. Significantly, if ice retreat is triggered, there are no relatively shallow points in the ice sheet bed along the course of Pine Island and Thwaites glaciers to prevent possible runaway ice retreat into the interior of West Antarctica. The results are published in the journal Nature.
"Today, the Pine Island and Thwaites glaciers are grounded in a very precarious position, and major retreat may already be happening, caused primarily by warm waters melting from below the ice shelves that jut out from each glacier into the sea," said Matthew Wise of Cambridge's Scott Polar Research Institute, and the study's first author. "If we remove these buttressing ice shelves, unstable ice thicknesses would cause the grounded West Antarctic Ice Sheet to retreat rapidly again in the future. Since there are no potential restabilising points further upstream to stop any retreat from extending deep into the West Antarctic hinterland, this could cause sea-levels to rise faster than previously projected."
EDIT
https://phys.org/news/2017-10-scars-left-icebergs-west-antarctic.html
