Abstract
AbstractSupraglacial ponds on debris-covered glaciers present a mechanism of atmosphere/glacier energy transfer that is poorly studied, and only conceptually included in mass-balance studies of debris-covered glaciers. This research advances previous efforts to develop a model of mass and energy balance for supraglacial ponds by applying a free-convection approach to account for energy exchanges at the subaqueous bare-ice surfaces. We develop the model using field data from a pond on Lirung Glacier, Nepal, that was monitored during the 2013 and 2014 monsoon periods. Sensitivity testing is performed for several key parameters, and alternative melt algorithms are compared with the model. The pond acts as a significant recipient of energy for the glacier system, and actively participates in the glacier’s hydrologic system during the monsoon. Melt rates are 2-4 cm d-1 (total of 98.5 m3 over the study period) for bare ice in contact with the pond, and <1 mmd-1 (total of 10.6m3) for the saturated debris zone. The majority of absorbed atmospheric energy leaves the pond system through englacial conduits, delivering sufficient energy to melt 2612 m3 additional ice over the study period (38.4 m3 d-1). Such melting might be expected to lead to subsidence of the glacier surface. Supraglacial ponds efficiently convey atmospheric energy to the glacier’s interior and rapidly promote the downwasting process.
Highlights
Debris-covered glaciers comprise 10% of the glacierized area in High Mountain Asia, where many glaciers have been rapidly losing mass in recent years (Benn and others, 2012; Bolch and others, 2012; Pellicciotti and others, 2015)
Several studies have shown that surface ponds and terminal lakes of debris-covered glaciers are associated with rapid thinning (Basnett and others, 2013; Pellicciotti and others, 2015) and retreat (Benn and others, 2000; Gardelle and others, 2011; Sakai, 2012)
The diurnal peaks in stored energy are supplied by the residual of the pond surface energy balance (Eqn (3)), which often peaks above 1000 W mÀ 2 (Fig. 5a and f)
Summary
Debris-covered glaciers comprise 10% of the glacierized area in High Mountain Asia, where many glaciers have been rapidly losing mass in recent years (Benn and others, 2012; Bolch and others, 2012; Pellicciotti and others, 2015). The insulating effect of thick debris is known to reduce ablation (Østrem, 1959; Scherler and others, 2011; Ragettli and others, 2015), the impact of surface ponds and their associated ice cliffs on the ablation process is much less understood (Sakai and others, 2000; Benn and others, 2001, 2012; Röhl, 2006). Several studies have shown that surface ponds and terminal lakes of debris-covered glaciers are associated with rapid thinning (Basnett and others, 2013; Pellicciotti and others, 2015) and retreat (Benn and others, 2000; Gardelle and others, 2011; Sakai, 2012). A conceptual model of debris-covered glacier response to climate change has been advanced, linking supraglacial pond development to subsequent terminal lake formation (Benn and others, 2000; Reynolds, 2000; Quincey and others, 2007; Benn and others, 2012). Observations have highlighted key melt mechanisms associated with ponds, including calving and waterline melting (Reynolds, 2000; Benn and others, 2001; Röhl, 2008), and the rapid backwasting of bare-ice cliffs that are often adjacent to them (Benn and others, 2001; Han and others, 2010; Reid and Brock, 2014; Steiner and others, 2015)
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