New research reveals how ocean warming triggered the large-scale retreat of the Northeast Greenland Ice Stream (NEGIS) - offering vital clues for understanding its modern-day vulnerability.
NEGIS is the largest ice stream draining the Greenland Ice Sheet into the ocean.
It contains enough ice to raise global sea level by 1.1 to 1.4 metres.
Its stability is therefore critical for future sea-level projections.
A team led by researchers from our Department of Geography and Newcastle University has reconstructed the behaviour of NEGIS over the last 20,000 years - since the end of the Last Glacial Maximum.
They showed that oceanic processes, not just atmospheric changes, played a decisive role in past episodes of rapid ice retreat.
Vulnerable to temperature rise
The researchers found that when an ice stream's grounding line (where ice lifts off from its bed and begins to float), is exposed to warm ocean water, the ice stream and its ice shelves become much more vulnerable to retreat and collapse.
The team found that an initial period of retreat occurred between 20,300 and 17,600 years ago.
Air temperatures were still low at this point, around -20° to -15 °C lower than present.
This suggests that warm Atlantic Water reaching the base of the ice stream was the main driver for this early retreat via enhanced melt.
The geological record then shows a period of distinctive ice shelf collapse triggered by the further ingress of warm Atlantic Water and enhanced sub-ice shelf melt around 15,000 yrs ago.
This was combined with a rapid rise in air temperatures which undoubtedly drove surface thinning.
Together, both forcing mechanisms drove ice shelf disintegration, ultimately causing grounding line instability and ice retreat onto the inner continental shelf.
Critical role
The research took place as part of the wider project, 'Greenland in a Warmer Climate' led by our Geography Professor David Roberts.
Professor Roberts stressed how critical it has been to understand the past dynamic behaviour of NEGIS.
This is because this highly sensitive sector of the Greenland Ice Sheet plays a critical role in controlling contemporary ice-ocean interaction in the Northeast Atlantic.
