Thermal structure of Svalbard glaciers and implications for thermal switch models of glacier surging

Abstract

Switches between cold‐ and warm‐based conditions have long been invoked to explain surges of High Arctic glaciers. Here we compile existing and new data on the thermal regime of six glaciers in Svalbard to test the applicability of thermal switch models. Two of the large glaciers of our sample are water terminating while one is land terminating. All three have a well‐known surge history. They have a thick basal layer of temperate ice, superimposed by cold ice. A cold terminus forms during quiescence but is mechanically removed by calving on tidewater glaciers. The other three glaciers are relatively small and are either entirely cold or have a diminishing warm core. All three bear evidence of former warm‐based thermal regimes and, in two cases, surge‐like behavior during the Little Ice Age. In Svalbard, therefore, three types of glaciers have switched from slow to fast flow: (1) small glaciers that underwent thermal cycles during and following the Little Ice Age (switches between cold‐ and warm‐based conditions), (2) large terrestrial glaciers which remain warm based throughout the entire surge cycle but develop cold termini during quiescence, and (3) large tidewater glaciers that remain warm based throughout the surge cycle. Our results demonstrate that thermal switching cannot explain the surges of large glaciers in Svalbard. We apply the concept of enthalpy cycling to the spectrum of surge and surge‐like behavior displayed by these glaciers and demonstrate that all Svalbard surge‐type glaciers can be understood within a single conceptual framework.

Bedrock Fracture Characteristics as a Possible Control on the Distribution of Surge‐Type Glaciers

“…We hypothesize the existence of a subglacial transition zone between fully or partially exposed bedrock upglacier and a matrix‐supported till‐covered bed downglacier (Figure ). We hypothesize that this transition zone is located at the terminal end of the ice reservoir, which is often found in the accumulation zone (e.g., Kamb et al, ; Stanley, ) even for surges where the propagation rate is controlled by a thermal transition at the bed (e.g., Sund et al, ; Sevestre et al, ). To provide the necessary resistance to flow during quiescence, this zone must exert greater drag than purely hard or purely soft beds.…”

“…Even the most fractured rocks have insufficient permeability to evacuate any significant fraction of the surface melt in this case; hence, we would not expect water flow through fractured bedrock to play an important role in controlling glacier type by means of regulating basal water pressure. Differences in the hydrological regimes that arise from the bedrock fracture spacing might lead to small differences in the water flux, but perhaps these differences are sufficient to alter the enthalpy balance in favor of surging (e.g., Sevestre & Benn, ; Sevestre et al, ). Such calculations could be explored in future research.…”

Holocene glacial evolution of Mohnbukta in eastern Spitsbergen

“…Sevestre & Benn ; Sevestre et al . ). This could have caused the Mohnbukta glaciers to surge sometime in the early Holocene leading to the deposition of the outer terminal moraine ridge.…”

Seismic Noise Interferometry Reveals Transverse Drainage Configuration Beneath the Surging Bering Glacier

“…These soft‐bed configurations can also sustain high water pressure over distributed areas to weaken the till layer and reduce basal resistance to ice flow. Current field observations do not seem able to distinguish the hard‐bed and soft‐bed configurations or whether there exists a single mechanism for surges (Harrison & Post, ; Murray et al, ; Pritchard, ; Sevestre et al, ).…”