Antarctic glacier retreat – From a Glaciers Perspective

Sjögren Glacier comparison in Landsat images from 2001 and 2016, red dots indicate terminus position, Point A, B, C and D are in fixed locations.

Sjögren Glacier flows east from the northern Antarctic Peninsula and prior to the 1980’s was a principal feeder glacier to Prince Gustav Ice Shelf. This 1600 square kilometer ice shelf disintegrated in the mid-1990’s and was gone in 1995 (Cook and Vaughan, 2010). Scambos et al (2014) noted a widespread thinning and retreat of Northern Antarctic Peninsula Glaciers with the greatest changes where ice shelf collapse had occurred, Sjögren Glacier being one of the locations. Scambos et al (2004) first documented the acceleration of glaciers that fed an ice shelf after ice shelf loss in the Larsen B region. A new paper by Seehaus et al (2016) focuses on long term velocity change at Sjögren Glacier as it continues to retreat. This study illustrates the acceleration is long lived with a peak velocity of 2.8 m/day in 2007 declining to 1.4 m/day in 2014, compared to a 1996 velocity of 0.7 m/day, which was likely already higher than the velocity in years prior to ice shelf breakup. Here we examine Landsat images from 1990, 2001, 2005 and 2016 to illustrate changes in terminus position of Sjögren Glacier

In the 1990 Landsat image Sjögren Glacier feed directly into the Prince Gustav ice Shelf which then By 1993 Seehaus et al (2016) note that Sjögren Glacier had retreated to the mouth of Sjögren Inlet in 1993, this is marked Point A on Landsat Images. By 2001 the glacier had retreated to Point B, a distance of 7 km. Between 2001 and 2005 Sjögren Glacier retreat led to a separation from Boydell Glacier at Point C. In 2016 Sjögren Glacier had retreated 10-11 km from the 2001 location, and 4.5 km from Point C up the expanding fjord. The production of icebergs remains heavy and the inlet does not narrow for another 6 km from the front. Seehaus et al (2016) Figure 1 indicates that the area of high velocity over 1 m/day extends 1 km upglacier, with somewhat of a slowdown at 6 km behind the front. The high velocity and limited change in fjord width in the lower 6 km indicates there is not a new pinning point to slow retreat appreciably in this stretch. Figure 1 also illustrates the retreat from 1993-2014. The pattern of ice shelf loss and glacier retreat after loss has also played out at Jones Ice Shelf and Rohss Bay.

1990 Landsat Image of Sjogren Glacier and Prince Gustav Ice Shelf, terminus marked by red dots

2005 Landsat Image of Sjogren Glacier, terminus marked by red dots

Prospect Glacier flows into the Sea on the E=West Coast of Antarctica. The glacier used to drain into the Wordie Ice Shelf which was formerly located at 69o on the west coast of the Antarctic Peninsula. In a joint study released by the USGS and British Antarctic Survey (BAS) the history of the Wordie Ice Shelf is reviewed. Below is the view in a Landsat 1979 image of the ice shelf. . The ice shelf advanced from 1947 to 1966. The ice shelf advanced on the northern end and retreated on the southern end from 1966 to 1974. The retreat at the southern end where Prospect Glacier fed the ice sheet was 1-2 km. By 1989 an additional 2 km of retreat had occurred. From 1989 to 1997 a general advance of the ice shelf occurred. From 1999 to 2001 retreat of 3-10 km occurred which marked the end of the ice shelf. The retreat is summarized in a figure from the USGS(2011). . The demise of the Wordie Ice Shelf was first documented by D.Vaughan and C.Doake (1991) of the BAS. The USGS long term project of mapping the changes with Landsat has been led by R. Williams, C.Swithinbank and J.Ferrrigno Examination of recent Landsat imagery indicate continued retreat of Prospect Glacier like its neighbor Fleming Glacier since ice shelf loss. A comparison of the ice front in the Prospect Glacier area is indicated in Landsat imagery from 1989 (top), 2002 (middle) and 2009 (bottom). Mount Balfour is at the northern edge of the Prospect Glacier, and may well become an island. The retreat is more pronounced on the southern side of the glacier note the locations A-E are the same prominent mountain features in the 2002 and 2009 images. The terminus is retreating eastward along Mount Balfour, from 1989-2002 but not significantly from 2002-2009. . A closeup view of the 2009 terminus indicates considerable rifting near the ice front, that represent icebergs that will soon calve off leading to further retreat. Surface melt in this area is quite limited, and the loss of the ice shelf through thinning and then rifting and breakup must have been triggered in part by increased basal melt. With the loss of the ice shelf, there is less back force slowing glacier motion at the ice front. The acceleration is leading to further thinning and continued extensive rifting. Rifts are indicated by red arrows and are likely due to basal crevasses expanding towards the surface.