The North East Greenland Ice Stream transports enormous amounts of ice from the heart of the island to the sea and thus also influences global sea levels. An international research team led by the Alfred Wegener Institute has now used a new evaluation method for airborne radar measurements to determine the age of the icy conveyor belt. According to the study, it only extended into the heart of Greenland around 2,000 years ago. The study, which opens up new possibilities for research into ice sheets, was recently published in the scientific journal Nature Communications.
![[Translate to English:] Mit Radarmessungen konnte das Forschungsteam ein dreidimensionales Modell der inneren Struktur des Eisstroms erstellen und sichtbar machen, wie der NEGIS die Eisschichten deformiert und faltet.](/fileadmin/_processed_/8/8/csm_KM_NEGIS_Alter_20240209_03_83203aed49.jpg)
The mass balance of the enormous Greenland ice sheet plays a decisive role in the rise in global sea levels. Between 2002 and 2023, the giant lost around 270 gigatons of ice per year because more mass was lost through meltwater and calving glaciers than was added by snowfall in the heart of the island. As a result, global water levels rose by an average of approximately 0.8 millimeters per year. Most of the loss occurs via a few ice streams – river-like areas within the shield where solid ice moves faster towards the sea than in the surrounding area. One of these "rivers" is the Northeast Greenland Ice Stream (NEGIS). It extends around 700 kilometers inland from the coast.
"We've used the radar on board the Polar 5 and 6 research aircraft to look inside NEGIS," explains Daniela Jansen, glaciologist at Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). "The electromagnetic waves penetrate deep into the ice, spread out to the bedrock, and are reflected there as well as at certain interfaces within the ice. Based on the transit time and amplitude of the reflected signals, we were able to create a three-dimensional model of the inner structure of the ice flow. This shows how NEGIS deforms and folds the ice layers." Using the deformation patterns, researchers can reconstruct how the flow developed and when the outflow from the region accelerated. This information remains stored in the ice for a long time.
Paul Bons, a structural geologist at the University of Tübingen, also played a key role in the study. He had the idea of using the data to determine the age of the ice flow. This is because the reflective boundary layers in the ice are former ice surfaces that were formed at the same time. Thanks to known data from ice cores, these layers of the same age (isochrones) can be linked to certain events - such as volcanic eruptions - and thus dated. Using these dated boundary layers, the time of internal ice deformation phases has now been determined for the first time. "Using this method, which is completely new for use in ice, we were able to determine that the ice stream in the region we investigated is comparatively young at just 2,000 years old," says Daniela Jansen. The results thus refute the widespread assumption among researchers that the NEGIS in its current form is a constant feature of the Greenland ice sheet.
"Ice streams can therefore form much faster than previously thought," explains the AWI glaciologist. "Accordingly, the rate at which ice flows from ice sheets into the sea and ultimately causes sea levels to rise can also increase very quickly. Our study thus shows that these currents and their variability need to be better incorporated into models that calculate future sea-level rise. We also provide a completely new structural geological approach for determining the age of such currents. Applying it to existing data and planning for future field research opens up many opportunities to learn more about the deformation history of ice sheets."
Original publication:
Jansen, D., Franke, S., Bons P. et al. Shear margins in upper half of Northeast Greenland Ice Stream were established two millennia ago. Nat Commun 15, 1193 (2024). https://doi.org/10.1038/s41467-024-45021-8