Major ice streams can close, changing the rapid transport of ice to other parts of the ice sheet, within a few thousand years. This was determined in reconstructions of two ice streams, based on ice-penetrating radar scans of the Greenland Ice Sheet, which a team of researchers led by the Alfred Wegener Institute has just presented in the journal Nature Geoscience .
How fast sea level rises in the future will depend largely on how dynamic or stable the Greenland ice sheet is: ice that, through its mass loss, has contributed approx. 40 mm to sea level rise since 1900. In addition to melting at its surface and base, the sheet loses mass through ice streams, essentially conveyor belts for the rapid transport of ice from the sheet interior to its edge. The routes of past ice streams can now be accurately reconstructed in the now glacier-free areas at the edge of the sheet, as the landforms they leave behind provide clearly visible clues. However, until recently very little was known about the activity of past ice streams in the Inner Greenland Ice Sheet, as the area is difficult to access. The answer: cutting-edge measurement technologies such as high-resolution radar systems (which can penetrate the ice to map structures several thousand meters below the surface of the ice sheet. As part of a project to reconstruct past ice streams in cooperation with the teacher). Paul Bons from the University of Tübingen, experts from the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI) used structural geology methods to analyze these images.
“Thanks to our ice-penetrating radar data, we can show how quickly the ice transport system of the Greenland ice sheet was reconfigured. Major ice streams can ‘turn off’ within a few thousand or even hundreds of years, while others appear elsewhere at a similar rate. Until now, no one had any idea that currents on this scale could change so quickly,” reports AWI glaciologist Dr Steven Franke, first author of the study. Ice transport involving the flow of solid, non-melting ice is a component of ice dynamics that needs to be more actively integrated into predictions of how much the Greenland ice sheet will contribute to the increase of sea level in various future climate scenarios. Current ice sheet models can only reflect those processes that are clearly understood. However, since there are no observations of ice stream instability, this aspect is not included in any model. The ice flow history, which is now visible by radar, provides information on the temporal and spatial evolution of this dynamic.
The data published in the study were collected in aerial campaigns with the AWI Polar 6 research aircraft and by NASA’s Operation IceBridge in northeast Greenland, where only very low flow velocities can currently be observed on the ice The team of researchers identified two paleo ice streams, which were once active and are now buried under several hundred meters of ice. Their analysis shows that these ice streams were active in the Holocene (less than 11,700 years ago) and extended far into the ice core of northeast central Greenland.
“The radar signature of one of the two paleo ice streams, which we used to reconstruct past ice stream activity, is remarkably similar to that of the massive and still active Northeast Greenland Ice Stream (NEGIS ),” says AWI glaciologist Dr. Daniela. Jansen, head of the Past Ice Streams Project that produced the publication. This discovery, he says, could offer new insights into the future behavior of NEGIS, whose formation and stability are the subject of considerable debate. The now published observations will allow researchers to understand in more detail the mechanisms responsible for producing and shaping ice streams. As a result, they can be more accurately represented in models designed to predict how our planet’s ice sheets will react to global warming.
Original post:
Steven Franke, Paul D. Bons, Julien Westhoff, Ilka Weikusat, Tobias Binder, Kyra Streng, Daniel Steinhage, Veit Helm, Olaf Eisen, John D. Paden, Graeme Eagles, Daniela Jansen: Closure of the Holocene Ice Stream and drainage basin reconfiguration in northeast Greenland; Nature Geoscience (2022). DOI: 10.1038/s41561-022-01082-2
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