Delta progradation in Greenland driven by increasing glacial mass loss

• Published in: Nature (London) 2017-10, Vol.550 (7674), p.101-104
• Main Authors: Bendixen, Mette, Lønsmann Iversen, Lars, Anker Bjørk, Anders, Elberling, Bo, Westergaard-Nielsen, Andreas, Overeem, Irina, Barnhart, Katy R., Abbas Khan, Shfaqat, Box, Jason E., Abermann, Jakob, Langley, Kirsty, Kroon, Aart
• Format: Article
• Language: English
• Subjects: 704/106/125; 704/106/242; 704/106/694/1108; Aerial photography; Air temperature; Arctic zone; Climate change; Coastal evolution; Coastal plains; Coastal zone; Coasts; Cryosphere; Deltas; Deposition; Earth; Environmental aspects; Environmental conditions; Erosion; Evolution; Fluxes; Fresh water; Freshwater ice; Glaciers; Greenland ice sheet; Human influences; Humanities and Social Sciences; Ice; Ice-free periods; Imagery; letter; multidisciplinary; Permafrost; Permafrost distribution; Remote sensing; Rivers; Runoff; Science; Sea ice; Sediments; Soil erosion; Surface-ice melting
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature23873

Climate change has the potential to erode coastlines, but a rediscovered archive of aerial photographs from the Second World War shows that in southern Greenland, deltas have recently extended seaward. Greenland's growing deltas Climate change has the potential to erode coastlines, for example as a result of increased wave activity, but the net effect depends on the balance between creative and destructive forces. Mette Bendixen and colleagues show that deltas in southwestern Greenland have grown over the past few decades, following a period of stability in the mid-twentieth century. The delta expansions occurred during periods of reduced sea ice and increased melt from the Greenland Ice Sheet. Although many coastlines remain under threat, these findings reveal the intimate interactions that arise in a warming climate. A loss of ice seems to lead to increased sediment delivery, which has resulted in the expansion, rather than degradation, of Greenland's deltas. Climate changes are pronounced in Arctic regions and increase the vulnerability of the Arctic coastal zone 1 . For example, increases in melting of the Greenland Ice Sheet and reductions in sea ice and permafrost distribution are likely to alter coastal morphodynamics. The deltas of Greenland are largely unaffected by human activity, but increased freshwater runoff and sediment fluxes may increase the size of the deltas, whereas increased wave activity in ice-free periods could reduce their size, with the net impact being unclear until now. Here we show that southwestern Greenland deltas were largely stable from the 1940s to 1980s, but prograded (that is, sediment deposition extended the delta into the sea) in a warming Arctic from the 1980s to 2010s. Our results are based on the areal changes of 121 deltas since the 1940s, assessed using newly discovered aerial photographs and remotely sensed imagery. We find that delta progradation was driven by high freshwater runoff from the Greenland Ice Sheet coinciding with periods of open water. Progradation was controlled by the local initial environmental conditions (that is, accumulated air temperatures above 0 °C per year, freshwater runoff and sea ice in the 1980s) rather than by local changes in these conditions from the 1980s to 2010s at each delta. This is in contrast to a dominantly eroding trend of Arctic sedimentary coasts along the coastal plains of Alaska 2 , Siberia 3 and western Canada 4 , and to the spatially variable patterns of erosion and