The Northeast Greenland Ice Stream is the largest conduit draining the Greenland Ice Sheet, holding enough ice to raise global sea level by 1.1 to 1.4 metres. Research led by Newcastle University's Louise Callard with colleagues at Durham University, published in Nature Communications, reconstructs its behaviour over the last 20,000 years and finds that the ocean, not the atmosphere, called the tune during its most dramatic retreats.
Using offshore records gathered on RV Polarstern expeditions in 2016 and 2017 with colleagues at the Alfred Wegener Institute, the team showed that an early phase of retreat between roughly 20,300 and 17,600 years ago occurred while air temperatures were still 15 to 20 degrees Celsius colder than today. Warm Atlantic water reaching the base of the ice stream drove that melt. Around 15,000 years ago, warm water pushed further beneath the ice shelf just as air temperatures rose sharply, and the shelf collapsed.
The NERC-funded study lands directly on the projections that matter today. The same ice-ocean feedbacks that dismantled the ice stream in the geological past are strengthening again as the Atlantic warms, and the authors argue that sea-level forecasts which underweight ocean forcing will systematically underestimate how quickly this giant of the Greenland Ice Sheet can retreat in the coming centuries.