The study, led by scientists at Newcastle University and Durham University, shows that ocean processes, not only atmospheric changes, played a decisive role in past episodes of rapid NEGIS retreat following the Last Glacial Maximum. By analysing geological evidence, the team linked periods when the grounding line of the ice stream was exposed to warm Atlantic Water with phases of enhanced melting, ice shelf weakening, and grounding line instability.
The researchers report that an initial retreat occurred between about 20,300 and 17,600 years ago, when regional air temperatures were still around 20 to 15 degrees Celsius lower than today. This implies that warm Atlantic Water reaching the base of the ice stream was the primary driver of this early phase of ice loss by increasing basal and sub - ice shelf melt despite the cold atmosphere.
The geological record then indicates a later phase of pronounced ice shelf collapse around 15,000 years ago, when warm Atlantic Water advanced farther beneath the ice and sub - ice shelf melt intensified. At the same time, air temperatures rose rapidly, thinning the ice from the surface; together, these oceanic and atmospheric influences led to disintegration of the ice shelf, grounding line retreat, and withdrawal of the ice margin onto the inner continental shelf.
Lead author Dr Louise Callard, Senior Lecturer in Physical Geography at Newcastle University, stated: "If the Northeast Greenland Ice Stream collapses, it has the potential to significantly raise global sea levels, so knowing what controls its behaviour is crucial. The palaeo record provides an unparalleled archive of past changes, allowing us to recognise what is driving current retreat. These findings highlight how important ice - ocean interactions are for understanding why modern ice sheets are retreating. Both observations and computer models must account for these ocean-driven processes."
The work forms part of the Greenland in a Warmer Climate project led by Durham University, which examines the dynamic behaviour of NEGIS and its role in controlling present-day ice - ocean interactions in the North East Atlantic sector. Principal Investigator Professor David Roberts of Durham University highlighted the importance of identifying feedbacks between ice sheets and the ocean for understanding current polar environmental change and for improving projections of future global sea-level rise.
Professor Roberts noted that a decade of research in this sector has constrained the long-term thinning and retreat history of NEGIS and clarified ice stream - ocean feedbacks. "Understanding the key feedbacks that control ice sheet/ocean interaction is important not only for contemporary environmental change around the poles, but also for predicting future global sea-level rise,"
Professor Roberts said. "As part of our work on this project over the last 10 years, we have not only constrained the long term thinning and retreat history of the NEGIS, but we now have a much better understanding of ice stream/ocean feedbacks. This paper is one of the first to recognise ice shelf break-up in the geological record in Greenland and it demonstrates the critical importance of high resolution, palaeoglaciological and palaeooceanographic reconstruction to the scientific community."
Research Report:Ocean driven retreat of the Northeast Greenland Ice Stream following the Last Glacial Maximum
Related Links
Newcastle University
Beyond the Ice Age
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