Fluctuations in the flow velocity of the Antarctic Shirase Glacier over an 11-year period

Temporal fluctuations in the flow velocity of Shirase Glacier in Antarctica were studied using 15 synthetic aperture radar (SAR) scenes obtained by the Japanese Earth Resources Satellite-1 (JERS-1) in 1996–1998 and 9 phased-array-type L-band SAR (PALSAR) scenes obtained by the Advanced Land Observing Satellite (ALOS) in 2007–2008. The scenes were analyzed using image correlation. The relative accuracy of the determined velocities was ±0.03 km/a for JERS-1 and ±0.02 km/a for ALOS. No marked temporal changes in ice-flow velocity at the grounding line (GL) were noted during either period; the ice velocity varied from 2.33 km/a (1996) to 2.27 km/a (2007). However, a marked difference between the two periods was found upstream from the GL on the central streamline, as a function of distance from the GL. Between the GL and the point 30 km downstream, ice velocities tended to be lower in 2007–2008 than in 1996–1998. Upstream from the GL, the velocities were higher in 2007–2008 than in 1996–1998, increasingly so with distance upstream, reaching a maximum of approximately 0.54 km/a at around 17–18 km upstream from the GL before diminishing again to a value of ∼0.25 km/a at 30 km upstream. No clear seasonal variations in flow velocity were observed at 17–18 km upstream from the GL in 1996–1998; however, in 2007–2008, the summer (December 2007–February 2008) velocity was 1.27 km/a, whereas the winter (June–August 2008) velocity was 1.06 km/a, representing a marked difference of 0.21 km/a. A larger difference between these seasons (0.38 km/a) was found at 20 km above the GL.