Antarctic ice sheet retreat slowed by ocean changes
Widespread collapse of a vast and globally important region of Antarctica is not inevitable at present, new research suggests.
A team of researchers from the Universities of Edinburgh, Cambridge and Washington used satellite imagery and climate and ocean records to obtain the most detailed understanding yet of how the West Antarctic Ice Sheet is responding to climate change.
Their research reveals that the pace and extent of ice destabilisation along this highly dynamic region of Antarctica varies according to differences in regional climate.
The researchers show that while the ice sheet – which contains enough ice to raise global sea level by 3.3 metres – continues to retreat, the pace of melting slowed across its most vulnerable region between 2003 and 2015.
The slowdown was driven by changes in surrounding ocean temperature, which were in turn caused by variations in offshore wind conditions, researchers say.
The ice sheet is home to the vast, unstable Pine Island and Thwaites glaciers. Since the early 1990s, scientists have observed an abrupt acceleration in ice melting and retreat across the region, which is attributed in part to human-induced climate change over the past century.
Previous studies have suggested this could signal the onset of an irreversible, ice-sheet-wide collapse, which would continue independently of any further changes to the climate.
The idea that once a marine-based ice sheet passes a certain tipping point it will cause a runaway response has been widely reported. Despite this, questions remain about the extent to which ongoing changes in climate still regulate ice losses along the entire West Antarctic coastline. Ultimately, our findings show that an intimate link still exists between the climate and how Antarctica’s most vulnerable glaciers are behaving. This suggests that runaway retreat is not inevitable at present. We have the ability to mitigate West Antarctic ice losses – if we curb carbon emissions in an aggressive way.
Using satellite observations, the team found distinct regional variations in how the ice sheet has changed since 2003. The pace of ice sheet retreat around the Amundsen Sea Sector slowed significantly compared to the neighbouring Bellingshausen Sea Sector, where it accelerated, the team say.
Newly available climate and ocean records were used to link these differences to changes in the strength and direction of offshore winds.
The icy ocean waters offshore of West Antarctica are battered by prevailing winds from the west. When the winds get stronger, they stir up warmer, saltier water from deep in the ocean, which reaches the Antarctic coastline and increases the rate of ice melt, the team says.
However, offshore of the Amundsen Sea Sector, the researchers show that the intensity of these winds reduced between 2003 and 2015, meaning lesser quantities of this deep, warm water reached the coastline.
The researchers found the cause of the weaker winds was an unusual drop in the Amundsen Sea Low pressure system situated offshore.
The researchers stress that further work is needed to examine how important such ice-ocean-climate interactions will be in the future amid a background of increasing marine ice sheet instability.
This study reinforces the urgent requirement to clarify how rapidly the most vulnerable regions of the West Antarctic Ice Sheet such as Thwaites Glacier will retreat, with global consequences for sea level rise. New data that we are currently acquiring from a traverse across Thwaites Glacier will directly address this goal.
The study is published in the journal Nature Communications.
The research was supported by the Carnegie Trust for the Universities of Scotland, the Scottish Alliance for Geoscience, Environment and Society, Albert II of Monaco Foundation, Natural Environment Research Council, US National Science Foundation, joint UK NERC/US NSF International Thwaites Glacier Collaboration project and European Space Agency.
Image credit: NASA/USGS