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.
Ice thickness, volume and subglacial topography of Urumqi Glacier No. 1, Tianshan mountains, central Asia, by ground penetrating radar survey
