Antarctic Peninsula 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

Pablo Zenteno in the Dept. of Geography at the University of Chile has called attention to Hariot Glacier is a close neighbor to Fleming Glacier draining the west side of the Antarctic Peninsula into Marguerite Bay. Both glaciers used to feed the Wordie Ice Shelf before it disintegrated between 1970 and 2000. Unlike the Fleming Glacier, Hariot Glacier has a steeper gradient as descends down a a mountain valley to the sea. The glacier is 6 kilometers wide in this valley. The glacier descends from 1500 m to 50 m as it passes through the valley. The tongue of this glacier has suffered a large loss since 2005. The 2005 Google Earth Image indicates a 50 square kilometer floating tongue beyond the grounding line, at the grounding line rifts developed on the west side of the glacier tongue. By 2009 in the Landsat 7 image overlain the floating tongue is gone. This retreat has been part of a progression that is illustrated by Zenteno (2010) . The spread of rifts have been noted as a sign of weakness in ice shelves note Fleming Glacier and Petermann Glacier. A closeup view of the rifts at the grounding line in 2005 that mark the inland point of the glacier tongue loss in 2009 indicate that the rifts extned 25% of the way across the glacier tongue. The amount of crevassing in the glacier tongue is unusual for a floating Antarctic Ice Shelf. Crevassing indicates acceleration which does not occur typically once a glacier is afloat. The crevassing either represents crevasses that developed before the section was afloat or an unstable floating section due to acceleration from the loss of the Wordie Ice Shelf.