Abstract
AbstractThe synthetic-aperture radar-interferometry technique is used to detect the migration of the limit of tidal flexing, or hinge line, of the floating ice longue of Peter-mann Gletscher, a major outlet glacier of north Greenland. The hinge line is detected automatically from differential interferograms using a model-fitting technique based on an elastic-beam theory. The statistical noise of the model fit is less than 3 mm, and the hinge line is mapped with a precision of 30 m. Following automatic registration of multidate image data to a precision of 5m, hinge-line migration is subsequently detected with a precision of 40 m in the horizontal plane across the glacier width. The results show that the hinge line of Petermann Gletscher migrates back and forth with tide by ±70m, in excellent agreement with the migration calculated from ocean tides predicted by a tidal model combined with the glacier surface and basal slope measured by an ice-sounding radar. Superimposed on the short-term hinge-line migration due to tide, we detect a hinge-line retreat of 270 m in 3.87 years which varies across the glacier width by ± 120 m. The retreat suggests glacier thinning at a rate of 78 + 35 cm ice a−1. Coincidentally, an analysis of ice-volume fluxes indicates that the hinge-line ice flux of Petermann Gletscher exceeds its balance flux by 0.88±1km3ice a−1, which in turn implies glacier thinning at 83+95cm ice a−1in the glacier lower reaches. Both methods therefore suggest that Petermann Gletscher is currently losing mass to the ocean.
Highlights
Th e tra nsiti o n regio n be twee n th e g ro und ed p a rt o f a n ice sheet a nd its fl oatin g part, ofte n rcferredto as th e g ro undin g line, is fund a m e nta l to the stabilit yoran ice s h ee t (Wee rtm a n, 197+; H ug hes, 1977; Thom as a nd Be ntl ey, 1978)
Two m a in feat ures are identifi ed fr om th e infer red profi les: (1) th e hinge lin e m ig ra tes bac k a nd fo rth on a short-te rm (d ays to month s) basis in both 1992 and 1996, whi ch \\-e interpret as a cha ngein ocean tid e; (2) the hinge line retreats seve ra l hundred meters b e tween 1992 and 1996, which we inte rpre- t as a cha nge in g lac ier thickness
Th e hinge-lin e migra ti o n across th e g lac ier w idth is 78±213 m be tween the two 1992 in terfc-rogram s a nd 42± 162 m between the two 1996 interferog rams
Summary
Th e tra nsiti o n regio n be twee n th e g ro und ed p a rt o f a n ice sheet a nd its fl oatin g part, ofte n rcferredto as th e g ro undin g line, is fund a m e nta l to the stabilit yoran ice s h ee t (Wee rtm a n, 197+; H ug hes, 1977; Thom as a nd Be ntl ey, 1978). \\'ith difTc re nti a l int e rfe rom e tr y, th e limit of tid a l fl ex ing of th e glac ie r, o r hinge line, m ay b e m eas ured a t a n unpreced ented IeITI of sp a ti a l d e tail a nd a cc uracy, simulta neo usly ac ross th e e ntire g lac ie r width, with a unifo rm samplin g scheme, ove r large a reas ( Ri g not, 199 6, 1998; Ri g no t a nd othe rs, 199 7) O\'C r flo a tin g tong ues and ice sh elves, th e m eas ured g lac ie r di splace m e nt is a combinatio n oC c ree p fl oll' a ndtid a llll o ti o n whic h ca n b e se pa ra ted u sing differe nti a l ( multipl e ) int erferogra m s (H a rtl a nd o th e rs, 199+). \\'ith difTc re nti a l int e rfe rom e tr y, th e limit of tid a l fl ex ing of th e glac ie r, o r hinge line, m ay b e m eas ured a t a n unpreced ented IeITI of sp a ti a l d e tail a nd a cc uracy, simulta neo usly ac ross th e e ntire g lac ie r width, with a unifo rm samplin g scheme, ove r large a reas ( Ri g not, 199 6, 1998; Ri g no t a nd othe rs, 199 7)
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