Former dynamic behaviour of a cold-based valley glacier on Svalbard revealed by basal ice and structural glaciology investigations

Abstract

ABSTRACT. Large numbers of small valley glaciers on Svalbard were thicker and more extensive during the Little Ice Age (LIA), demonstrated by prominent ice-cored moraines up to several kilometres beyond present-day margins. The majority of these glaciers have since experienced a long period of strongly negative mass balance during the 20th century and are now largely frozen to their beds, indicating they are likely to have undergone a thermal transition from a polythermal to a cold-based regime. We present evidence for such a switch by reconstructing the former flow dynamics and thermal regime of Tellbreen, a small cold-based valley glacier in central Spitsbergen, based on its basal sequence and glaciological structures. Within the basal sequence, the underlying matrix-supported diamict is interpreted as saturated subglacial traction till which has frozen at the bed, indicating that the thermal switch has resulted in a cessation of subglacial sediment deformation due to freezing of the former deforming layer. This is overlain by debris-poor dispersed facies ice, interpreted to have formed through strain-induced metamorphism of englacial ice. The sequential development of structures includes arcuate fracture traces, interpreted as shear planes formed in a compressive/transpressive stress regime; and fracture traces, interpreted as healed extensional crevasses. The formation of these sediment/ice facies and structures is indicative of dynamic, warm-based flow, most likely during the LIA when the glacier was significantly thicker.

Debris entrainment and landform genesis during tidewater glacier surges

“…Tectonic deformation is evident within the thin debris laminae in the dispersed facies, which often display a strong linear component indicative of shear (Figure 3b). Such features within basal ice sequences have been termed stretching lineations [e.g., Fleming et al, 2013;Lovell et al, 2015] and are similar to stringers commonly described from glacitectonized sediments [e.g., Roberts and Hart, 2005].…”

Topographic controls on plateau icefield recession: insights from the Younger Dryas Monadhliath Icefield, Scotland

“…The persistence of warm‐based active ice differs from recently documented changes in thermal regime from warm‐ to polythermal or cold‐based (e.g. Lovell et al ., ; Reinardy et al, ) and observed stagnation (e.g. Bradwell et al ., ) as a result of thinning at modern glaciers.…”

Structural glaciology of Austre Brøggerbreen, northwest Svalbard

“…Hambrey et al, 2005;Lovell et al, 2015), with many glaciers in Svalbard receding and thinning substantially since their Neoglacial maxima (c. 1900 AD). As climatic warming is most pronounced in the polar regions, it is necessary to understand how Arctic glaciers will respond to ongoing climate change.…”

“…The upwards migration of equilibrium lines and pronounced surface lowering of glaciers in Svalbard have revealed the internal structure of many ice masses in unprecedented detail. Recent structural glaciological research in Svalbard has primarily focused on structural controls on entrainment and transport of debris in polythermal and cold-based glaciers (Bennett, Hambrey, Huddart, & Ghienne, 1996;Boulton, van der Meer, Beets, Hart, & Ruegg, 1999;Hambrey & Glasser, 2003;Hambrey, Dowdeswell, Murray, & Porter, 1996;Hambrey, Bennett, Dowdeswell, Glasser, & Huddart, 1999;Hambrey et al, 2005;Hubbard, Glasser, Hambrey, & Etienne, 2004;Lovell et al, 2015). The map described in this paper documents the glacier-wide structural characteristics of Austre Brøggerbreen, a cold-based valley glacier in Svalbard.…”