Pervasive cold ice within a temperate glacier – implications for glacier thermal regimes, sediment transport and foreland geomorphology

Abstract

Abstract. This study suggests that cold-ice processes may be more widespread than previously assumed, even within temperate glacial systems. We present the first systematic mapping of cold ice at the snout of the temperate glacier Midtdalsbreen, an outlet of the Hardangerjøkulen icefield (Norway), from 43 line kilometres of ground-penetrating radar data. Results show a 40 m wide cold-ice zone within the majority of the glacier snout, where ice thickness is <10 m. We interpret ice to be cold-based across this zone, consistent with basal freeze-on processes involved in the deposition of moraines. We also find at least two zones of cold ice up to 15 m thick within the ablation area, occasionally extending to the glacier bed. There are two further zones of cold ice up to 30 m thick in the accumulation area, also extending to the glacier bed. Cold-ice zones in the ablation area tend to correspond to areas of the glacier that are covered by late-lying seasonal snow patches that reoccur over multiple years. Subglacial topography and the location of the freezing isotherm within the glacier and underlying subglacial strata likely influence the transport and supply of supraglacial debris and formation of controlled moraines. The wider implication of this study is the possibility that, with continued climate warming, temperate environments with primarily temperate glaciers could become polythermal in forthcoming decades with (i) persisting thinning and (ii) retreat to higher altitudes where subglacial permafrost could be and/or become more widespread. Adversely, the number and size of late-lying snow patches in ablation areas may decrease and thereby reduce the extent of cold ice, reinforcing the postulated change in the thermal regime.

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.…”

Evolution of the Norwegian plateau icefield Hardangerjøkulen since the ‘Little Ice Age’

“…The features result from differential melting of the glacier beneath the debris cover, leading to ice-cored ridges of sorted sands and gravels, which eventually become detached from the glacier ('controlled moraine'; cf. Evans, 2009; see also Reinardy et al, 2019). These were described by Andersen and Sollid (1971) under the term 'stratified moraine'.…”

Processes of ‘hummocky moraine’ formation in the Gaick, Scotland: insights into the ice‐marginal dynamics of a Younger Dryas plateau icefield

“…Recent geophysical investigations have also revealed that plateau icefield outlets may be thermally complex, with the identification of cold‐ice zones within a temperate outlet (Midtdalsbreen) of Hardangerjøkulen, Norway (Reinardy et al . ). The presence of these cold‐ice zones, together with the penetration of permafrost beneath the glacier margin, is thought to be crucial to the transport of basal material to englacial and supraglacial positions (see also Etzelmüller et al .…”

“…The penetration of awinter coldwave and seasonal cold-based conditions have been recognized as playing an important role at temperate glacier margins, although the mechanism of moraine formation (basal freeze-on) is different to those recognized in the Gaick (Andersen & Sollid 1971;Kr€ uger 1993Kr€ uger , 1995Kr€ uger , 1996Matthews et al 1995;Evans & Hiemstra 2005;Reinardy et al 2013;Chandler et al 2016a). Recent geophysical investigations have also revealed that plateau icefield outlets may be thermally complex, with the identification of cold-ice zones within a temperate outlet (Midtdalsbreen) of Hardangerjøkulen, Norway (Reinardy et al 2019). The presence of these cold-ice zones, together with the penetration of permafrost beneath the glacier margin, is thought to be crucial to the transport of basal material to englacial and supraglacial positions (see also Etzelm€ uller et al 2005).…”