A new study published in Nature Communications adds to the growing body of evidence that recent ice loss from the Antarctic Ice Sheet may signal the beginning of a prolonged period of ice sheet retreat and substantial global sea level rise.
The study, co-authored by Professor Nicholas Golledge from the Antarctic Research Centre at Te Herenga Waka—Victoria University of Wellington, uses geological data from Antarctica to understand how recent changes compare with those in the past.
“In the last two decades, the Antarctic Ice Sheet has suddenly started losing ice, contributing to rising sea levels around the world. Computer models that reproduce this recent acceleration indicate the ice sheet may have passed a critical tipping point leading to irreversible loss of parts of the ice sheet below sea level,” Professor Golledge said.
“Our study reveals that during times in the past when the ice sheet retreated, periods of rapid mass loss ‘switched on’ very abruptly, within only a decade or two. Once destabilised, the ice sheet continued to retreat for several hundred years before it quickly ‘switched off’ again, also taking only a couple of decades.”
When the world warmed at the end of the ice age, the Antarctic Ice Sheet went through many of these on/off episodes, each time contributing to global sea level rise, he said.
Evidence for this comes from gritty sediments released from melting icebergs that settled into mud on the sea floor.
Lead author Dr Michael Weber, from the Institute of Geosciences at the University of Bonn, headed the team that recovered cores of this sediment from the Southern Ocean.
By counting the amount of this iceberg-rafted sediment through the core, the scientists were able to identify eight phases with high amounts of debris, which they interpreted as retreat phases of the Antarctic Ice Sheet.
Each phase showed the same pattern—the ice sheet destabilised within a decade, contributed to global sea-level rise for centuries to a millennium, and then subsequently re-stabilised equally rapidly.
Combining the sediment record with computer models of ice sheet behaviour, the team showed each episode of increased iceberg calving reflected increased ice loss from the interior of the ice sheet, not just changes in the already-floating ice shelves.
“We found that iceberg calving events on multi-year time scales happened at the same time as the loss of grounded ice from the Antarctic Ice Sheet”, said Professor Golledge, who led the ice sheet modelling.
Study co-author Dr Zoë Thomas, from the University of New South Wales in Sydney, Australia, applied statistical methods to the model outputs that confirmed early warning signs could be detected for tipping points in the ice sheet system.
“If it just takes one decade to tip a system like this, that’s actually quite scary because if the Antarctic Ice Sheet behaves in future like it did in the past, we must be experiencing the tipping right now,” Dr Thomas said.
“Our findings are consistent with a growing body of evidence suggesting the acceleration of Antarctic ice-mass loss in recent decades may mark the start of a self-sustaining and irreversible period of ice sheet retreat and substantial global sea level rise,” Dr Weber said.
For more information, contact Professor Nicholas Golledge on nicholas.golledge@vuw.ac.nz or 021 665 942.
Publication: “Decadal-scale onset and termination of Antarctic ice-mass loss during the last deglaciation” by Michael E. Weber, Nicholas R. Golledge, Chris J. Fogwill, Chris S.M. Turney and Zoë A. Thomas. Nature Communications.