South georgia glacier retreat climate change – From a Glaciers Perspective

Neumayer Glacier (N) in 1999 and 2020 Landsat images. Red arrow is 1999 terminus position, pink arrow 2016 terminus location and yellow arrow March 2020 terminus location. K=Konig and T=Three Brothers Tributary, L=glacial lake.

Neumayer Glacier, South Georgia is a calving glacier that has been retreating rapidly since 1993 that was dynamically connected to the Konig Glacier along its southern margin just where the glacier turns northeast The glacier ends in a fjord that until recently was too short to be given a name, that empties into Cumberland Bay. Gordon et al., (2008) observed that larger tidewater and sea-calving valley and outlet glaciers generally remained in relatively advanced positions until the 1980’s. After 1980 most glaciers receded; some of these retreats have been dramatic (NASA, 2017). The BAS has a mapping function that provides glacier front positions since early in the 20th century (Cook et al 2010). For Neumayer Glacier the 1938 position is 3.5 km down fjord from the 2006 position. There was essentially no retreat up to 1974 and limited retreat up to 1993. Here we examine 1999-2020 Landsat imagery to identify glacier change.

In 1999 and 2002 the glacier extends passed the junction with Konig Glacier terminating in 2 km wide calving front. By 2002 the glacier had retreated 0.5 km, by 2006 1.8 km, by 2011 3.0 km and by 2016 5.3 km. A glacier dammed lake (L) along the north shore of the fjord no longer exists in 2016 and one tributary from the south is no longer connected. The glacier appears to have retreated into a deeper section of the fjord then where it ended from 1970-2002. The glacier is on the verge of separation into two main tributaries, Konig and Neumayer. In 2016 the calving front is 1.6 km long for Neumayer. Konig Glacier has a 1.3 km long tidewater front, but has limited calving. In 2018 I reported that the glaciers had separated (Pelto, 2018), with Neumayer Glacier still being in rapid retreat and Konig Glacier changing little. A tributary (T) from the south that parallels the Three Brothers Range, is still connected to Neumayer Glacier. In January 2020 the glacier remains connected to tributary (T). By early March 2020 the glacier has further retreated separating from tributary (T). The total retreat from 1999-2020 is 8.8 km, a retreat rate of over ~420 m/year. In the BAS map it is evident that there is a smaller slope change 2 km from the current terminus and a large slope change 5 km from the current terminus. The former may represent the end of the fjord or at least a significant shallower. The latter slope change is certainly the end of the low slope valley reach of the glacier, whether that be a shallow fjord or not. This is one of the most dramatic South Georgia glacier retreats along with Ross and Hindle Glacier (Pelto, 2017). Cook et al (2010) noted the average retreat of glaciers in this area of South Georgia of 60 m/year for the

Neumayer Glacier (N) in 2002 and 1-2020Landsat images.Red arrow is 2002 terminus position, pink arrow 2016 terminus location and yellow arrow March 2020 terminus location. K=Konig and T=Three Brothers Tributary.

Neumayer Glacier (N) in 2016 and 2018 Landsat images. Red arrow is 2002 terminus position, pink arrow 2016 terminus location and yellow arrow March 2020 terminus location. K=Konig and T=Three Brothers Tributary.

Neumayer Glacier (N) in South Georgia GIS Map from the BAS showing terminus change.

Novosilski Glacier in Landsat images from 2001 and 2018. Red arrow indicates 2001 terminus location, yellow arrow the 2018 terminus location, pink arrows the fringing grounded sections of marginal ice.

Novosilski Glacier is a large tidewater outlet glacier on the west (cloudier) coast of South Georgia terminating in Novosilski Bay It shares a divide with the rapidly retreating Ross and Hindle Glacier on the east coast. Gordon et al. (2008) observed that larger tidewater and calving outlet glaciers generally remained in relatively advanced positions from the 1950’s until the 1980s. After 1980 most glaciers receded; some of these retreats have been dramatic. The change in glacier termini position have been documented by Cook et al (2010) at British Antarctic Survey in a BAS retreat map, identified that 212 of the Peninsula’s 244 marine glaciers have retreated over the past 50 years and rates of retreat are increasing. Pelto (2017) documented the retreat of 11 of these glaciers during the 1989-2015 period. Here we examine Landsat images from 2001-2018 and the British Antarctic Survey GIS of the island to identify the magnitude of glacier change.

In 2001 Novosilski Glacier terminated in shallow water just east of a small island that acted as a pinning point, red arrow. By 2009 the glacier had retreated only a minor amount from this island into deeper water. A rapid retreat ensued and by 2016 the glacier had retreated into a narrower fjord reach. The north and south margins featured remanant ice that was based above tidewater, pink arrows. The blue arrows in the 2016 Landsat image indicating the large accumulation area feeding Novosilski. By 2018 the 2 km wide calving front had retreated 2.5 km from the 2001 position. There is little evident thinning upglacier of the terminus and, there is a significant increase in surface slope suggesting that unless calving rate increases, the terminus can remain near its current position. The snowline is low below 500 m in each of the satellite images of the glacier. This is not a particularly hospitable section of coastline and the BAS has only identified Gentoo Penguins having colonies in the area.

Novosilski Glacier in Landsat image from 2016. Red arrow indicates 2001 terminus location, yellow arrow the 2018 terminus location, pink arrows the fringing grounded sections of marginal ice, and blue arrows the glacier flow directions. Below is the South Georgia BAS map of the area indicating glacier margin position and elevation contours.