Acceleration of Pine Island Glacier Ice Shelf

Abstract

The Pine Island Glacier is one of the fastest ice streams in West Antarctica. It empties into a small ice shelf, bordering the Amundsen Sea, that is commonly considered part of this glacier system. Previous investigations of this glacier, based on Landsat images of the early to mid-1970s, estimated a velocity of 2.1-2.4 km/yr at the ice front. Recent studies have determined velocities on the order of 2.6-2.8 km/yr at the front. The discrepancy may be due to errors in positional control of the early Landsat images, or it may reflect a true acceleration. To determine whether the apparent velocity increase is real, we coregistered several sets of earlier images to a Landsat 7 ETM+ image of 2000. The sets include Landsat MSS images of 1973 and 1975, ERS SAR images of 1994 and 1996, and Landsat TM images of 1997 and 2000. Velocities were obtained by feature tracking and were restricted to the floating, ice-shelf part of the glacier. Velocities for the interval 1973 to 1975 ranged from 2.21-2.37 km/yr. For the same area, velocities for 1994 to 1996 ranged from 2.46-2.81 km/yr, and for 1997 to 2000 from 2.54-2.84 km/yr. The spread in velocities for each image set is mostly due to slower moving ice near the margin. According to the above data, in the central fast part, the ice shelf accelerated by more than 400 m/yr between about 1974 and 1995. The acceleration between about 1995 and 1999 is only around 50 m/yr. The total acceleration between about 1974 and 1999 is nearly 500 m/yr. These data indicate the majority of the acceleration took place before the mid-1990s, and it has decreased somewhat since then. However, whether the increase in velocity occurred mostly in the 1970s or was more evenly distributed over the mid-1970 to mid-1990 period can only be determined with intervening data. Rignot and others (in press) noted an acceleration of the Pine Island Glacier between 1992 and 2000 using ERS images; they suggest an increase in basal lubrication as a probable cause. A large calving event in the early 1970s may have contributed to the acceleration within the ice-shelf part, especially if the pre-calving ice shelf was pinned. Overall, our data support a general increase in velocity.