Seasonal to decadal scale variations in the surface velocity of Jakobshavn Isbrae, Greenland: Observation and model-based analysis

• Published in: Journal of Geophysical Research: Earth Surface Vol. 117; no. F2
• Main Authors: Joughin, Ian, Smith, Ben E., Howat, Ian M., Floricioiu, Dana, Alley, Richard B., Truffer, Martin, Fahnestock, Mark
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01.06.2012; American Geophysical Union
• Subjects: Acceleration; Analysis; Buttresses; Cryosphere; Driving ability; Earth sciences; Earth, ocean, space; Exact sciences and technology; Floating ice; Flotation; Flow resistance; glacier; Glacier retreat; Glaciers; glaciology; ice stream; Satellite observation; Seasonal variation; Seasonal variations; Surface velocity; Thickening; Thinning; Traction; Winter; polar regions; Arctic region; Greenland; troughs; glaciers; satellites; stress; models; Space remote sensing; Summer; Satellite observation; cycles; pressure; Floating ice; acceleration; new data; Thinning; Dynamical evolution; Winter; Flow velocity; geometry; Polar region; flotation; seasonal variations; Thickening
• ISSN: 0148-0227; 2169-9003; 2156-2202; 2169-9011
• DOI: 10.1029/2011JF002110

Using new data, we build upon the nearly two‐decade long record of observations from Jakobshavn Isbrae to investigate the processes driving its dynamic evolution. While winter flow speed has not increased substantially over the last three winters, there remains a strong seasonal variation in flow speed that coincides with a cycle of summer thinning and winter thickening. We relate changes in glacier speed to geometry through variations in basal traction and horizontal stresses, using ice‐flow models constrained by satellite and airborne observations. These results suggest that the bed provides little flow resistance along the main trough within about 20 km of the terminus. While the loss of buttressing from the retreat of grounded and floating ice likely contributed to the initial speedup, other processes are of comparable significance at seasonal to decadal time scales. From analysis of the models, we hypothesize that thinning‐induced change in basal effective pressure is the dominant process influencing near‐terminus behavior, while diffusive processes drive the upstream response. The apparent need for the terminus to thin to near flotation before it can calve may limit the rate at which retreat occurs. Our analysis of the processes controlling the speed suggests little potential for further large acceleration. Thinning and elevated speeds may continue at rates similar to present, however, putting the glacier on course to retreat to the head of its deep trough in about a century, at which point it likely would stabilize with a thinner terminus. Key Points The speedup of Jakobshavn Isbrae resulted from several processes The speedup did not result from buttressing alone The glacier likely will not speed up much more over the next century