Abstract
AbstractFrontal ablation from tidewater glaciers is a major component of the total mass loss from the Greenland ice sheet. It remains unclear, however, how changes in atmospheric and oceanic temperatures translate into changes in frontal ablation, in part due to sparse observations at sufficiently high spatial and temporal resolution. We present high-frequency time-lapse imagery (photos every 30 min) of iceberg calving and meltwater plumes at Kangiata Nunaata Sermia (KNS), southwest Greenland, during June–October 2017, alongside satellite-derived ice velocities and modelled subglacial discharge. Early in the melt season, we infer a subglacial hydrological network with multiple outlets that would theoretically distribute discharge and enhance undercutting by submarine melt, an inference supported by our observations of terminus-wide calving during this period. During the melt season, we infer hydraulic evolution to a relatively more channelised subglacial drainage configuration, based on meltwater plume visibility indicating focused emergence of subglacial water; these observations coincide with a reduction in terminus-wide calving and transition to an incised planform terminus geometry. We suggest that temporal variations in subglacial discharge and near-terminus subglacial hydraulic efficiency exert considerable influence on calving and frontal ablation at KNS.
Highlights
Ice discharge from tidewater glaciers is responsible for ∼50% of the total mass loss from the Greenland ice sheet (GrIS) (Shepherd and others, 2020), with this loss due to frontal ablation, comprising both iceberg calving and submarine melting (van der Veen, 2002; Benn and others, 2007)
Our detailed observations of terminus calving, frontal ablation, plume activity, ice velocity and modelled runoff reveal that the spatial distribution of subglacial runoff at the grounding line of a large tidewater glacier in Greenland exerts a strong control on calving frequency and frontal ablation during the melt season
At the start of the melt season, we infer a distributed and inefficient near-terminus subglacial drainage system, which theoretically exposes a large proportion of the terminus to plume-enhanced submarine melting, promoting widespread terminus undercutting and rapid frontal ablation
Summary
Ice discharge from tidewater glaciers is responsible for ∼50% of the total mass loss from the Greenland ice sheet (GrIS) (Shepherd and others, 2020), with this loss due to frontal ablation, comprising both iceberg calving and submarine melting (van der Veen, 2002; Benn and others, 2007). Submarine melt rates across the calving margin (and the resultant terminus undercutting and enhanced iceberg calving) are driven in part by spatial and temporal variations in the discharge of subglacial meltwater at glacier termini. This in turn is partly controlled by the routing of meltwater through the near-terminus subglacial hydrological system, the configuration of which may vary through a melt season (Slater and others, 2017). At other times the subglacial drainage may be in a comparatively distributed configuration, with subglacial runoff shared between multiple, smaller outlets at the grounding line (e.g. Slater and others, 2015) This means that the delivery of an equivalent volume of subglacial meltwater to a glacier terminus, within different
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