Changing Thermal Regime of Polythermal Glaciers

Over the past few decades, many Arctic glaciers have been shrinking in response to climate change and are predicted to shrink further over the next few decades. Many Arctic glaciers are polythermal, with warm ice (at 0^oC) in their interior where ice is thick and is warmed to the pressure melt point, and cold ice (below 0^oC) around their margins where ice is thin. Previous work on the polythermal glacier Midre Lovénbreen, close to the Arctic research base, Ny-Ålesund on Spitsbergen (Figures 1 & 2) has shown that the thermal regime of this glacier, particularly the location of warm-based and cold-based ice, has important implications for the glacier’s hydrology and dynamics (Rippin et al, 2005a, b). We hypothesized that as glaciers shrink, their thermal regime will change, and that this will affect the way in which water moves through them and control their movement. With this in mind, we visited Midre Lovénbreen in April/May 2006 and used a sled-mounted 50MHz Ground Penetrating Radar (GPR) pulled by skidoo to map the distribution of warm and cold ice across the glacier tongue (Figures 3 & 4). We have been able to compare the results with earlier GPR surveys undertaken in May 1990 and May 1998 (Figure 5). Results show that while the glacier snout has retreated about 13m per year and surface mass balance has been -0.4m of water equivalent per year since 1990, the boundary between the warm- and cold-based ice has retreated by around 80m per year over the same period.

In addition to the work on Midre Lovénbreen, we also undertook the first GPR survey of the adjacent Austre Lovénbreen (Figures 1 & 2). From this, we have been able to map the thickness of the entire glacier, in addition to the thickness of warm and cold ice. We can confirm this glacier is polythermal, like its neighbour. We plan to monitor the continued changes to the thermal regime of these glaciers over the next few years, and use the data to drive and test a numerical model of glacier flow, applicable for valley glaciers.

This work is being done in collaboration with David Rippin (University of Hull), Jack Kohler (Norsk Polar Institute, Tomsø, Norway), Jiawen Ren (Cold & Arid Regions Environment & Engineering Institute, Chinese Academy of Sciences) and Ming Yan (Polar Research Institute of China).

References

• Björnsson, H. & 6 others. 1996. The thermal regime of sub-polar glaciers mapped by multi-frequency radio-echo sounding. Journal of Glaciology, 42(140), 23-32.
• Rippin, D.M., Willis, I.C. and Arnold, N.S. 2005a. Seasonal patterns of velocity and strain across the tongue of the polythermal glacier Midre Lovénbreen, Svalbard. Annals of Glaciology, 42, 445-454.
• Rippin, D.M., Willis, I.C., Arnold, N.S., Hodson, A.J. and Brinkhaus, M. 2005b. Spatial and temporal variations in surface velocity and basal drag across the tongue of the polythermal Midre Lovénbreen, Svalbard. Journal of Glaciology, 51, 588-600.

Papers relating to this project

• Rippin, D.M., Willis, I.C. and Kohler, J. Submitted. Rapid changes in the thermal regime of the polythermal glacier Midre Lovénbreen, Svalbard in response to a changing climate. Journal of Geophysical Research.
• Willis, I.C., Rippin, D.M. and Kohler, J. 2007. Thermal regime changes of the polythermal Midre Lovénbreen, Svalbard. In The Dynamics and Mass Budget of Arctic Glaciers (Extended Abstracts). IASC Working Group on Arctic Glaciology Meeting. Pontresina (Switzerland). IMAU.
• Rippin, D., Willis, I., Arnold, N., Hodson, A., Moore, J., Kohler, J. and Bjornsson, H. 2003. Changes in geometry and subglacial drainage of Midre Lovénbreen, Svalbard, determined from digital elevation models. Earth Surface Processes and Landforms, 28, 273-298.

Figures

Figure 1. Map showing location of Midre Lovénbreen and Austre Lovénbreen, NW Spitsbergen, Svalbard.

Figure 2. Looking towards Midre Lovénbreen (top) and Austre Lovénbreen (bottom) from Ny-Ålesund in the winter (photo: David Rippin) and summer (photo: Andrew Wright).

Figure 3. Shaded surface digital elevation model (DEM; elevations in metres) of Midre Lovénbreen derived from 2005 LiDAR data. DEM resolution is 20 × 20 m. Red tracks mark the GPR survey lines collected in 2006 over the trunk of the glacier, and the superimposed yellow lines indicate the along-track and cross-track lines illustrated in Figure 4.

Figure 4: (A) GPR transect parallel with the glacier centreline (flow direction from left to right). The glacier surface is clearly visible as is the bed to the right of the image. To the left, the bed becomes obscured by a zone of intense scattering, which we interpret to be warm ice. (B) Cross-glacier GPR transect. The glacier surface is clearly visible as is the bed across most of the image, apart from in the central, deepest portion. Here, the bed is obscured by a zone of intense scattering, which we interpret to be warm ice. (C) and (D) are identical image to (A) and (B) respectively, but with red lines marking the glacier surface, bed and cold temperate transition surface (CTS), as well as zones of cold and warm ice labelled. Location of lines on the glacier is marked in Figure 1.

A  B  C 

Figure 5. GPR tracks across Midre Lovénbreen collected in: (A) May 1990 (Björnsson et al., 1996); May 1998 (Moore, unpublished; cf. Rippin et al., 2003); (C) May 2006. In all figures, blue indicates tracks where ice is cold throughout, while red indicates ice that has some thickness of warm basal ice. Tracks overly a surface DEM (see Figure 3 for details).