Seasonal speedup of a Greenland marine-terminating outlet glacier forced by surface melt–induced changes in subglacial hydrology

Peer reviewedPublisher PD

Variegated Glacier: A Century of Surges

ABSTRACT. A 1995 surge of Variegated Glacier, Alaska, USA, is discussed in the context of its six 20thcenturypredecessors, especially the previous surge in 1982/83 which was studied in detail. The averagetime between surge initiations is 15 years. The 1995 surge was considerably weaker than itspredecessors, having a single phase or at most a very weak second phase. The 1995 surge confirmsthat there is a seasonal cycle, with surge initiation in winter and termination in the first part of the meltseason, and a correlation between weather and both surge termination date and surge extent. Two daysof record high temperature correlated with the termination of the 1995 surge. The most obvious issue isthe absence of a strong second surge phase (as there was in the 1982/83 surge) culminating in a surgeextent more in line with that of the predecessors. This is considered in the light of a simple criterion forsurge initiation and re-initiation which depends upon the evolving basal shear stress

Penetration depth of interferometric synthetic-aperture radar signals in snow and ice

Digital elevation models of glaciated terrain produced by the NASA/Jet Propulsion Laboratory (JPL) airborne interferometric synthetic-aperture radar (InSAR) instrument in Greenland and Alaska at the C- (5.6 cm wave-length) and L-band (24-cm) frequencies were compared with surface elevation measured from airborne laser altimetry to estimate the phase center of the interferometric depth, or penetration depth, δp. On cold polar firn at Greenland summit, δp = 9±2m at C- and 14±4m at L-band. On the exposed ice surface of Jakobshavn Isbrae, west Greenland, δp = 1±2 m at C- and 3±3 m at L-band except on smooth, marginal ice where δp = 15±5 m. On colder marginal ice of northeast Greenland, δp reaches 60 to 120 m at L-band. On the temperate ice of Brady Glacier, Alaska, δp is 4±2 m at C- and 12±6 m at L-band, with little dependence on snow/ice conditions. The implications of the results on the scientific use of InSAR data over snow/ice terrain is discussed

Greenland Ice Sheet: Increased coastal thinning

Repeated laser-altimeter surveys and modelled snowfall/summer melt show average ice loss from Greenland between 1997 and 2003 was 80 ± 12 km3 yr, compared to about 60 km3 yr 1 for 1993/41998/9. Half of the increase was from higher summer melting, with the rest caused by velocities of some glaciers exceeding those needed to balance upstream snow accumulation. Velocities of one large glacier almost doubled between 1997 and 2003, resulting in net loss from its drainage basin by about 20 km of ice between 2002 and 2003