Temporal evolution of the Petermann Ice Shelf estuary constrained by satellite remote sensing observations

Supraglacial rivers may reduce ice-shelf instability by draining meltwater from the ice-shelf surface, limiting loading-induced stresses from ponded meltwater. However, if a supraglacial river incises to below sea level at the ice-shelf front, forming an estuary, this effect may be negated. Water flow reversal in the estuary loads the ice shelf, which induces flexural stress, limits meltwater export, and enhances melting. This phenomenon was first identified at Petermann Ice Shelf, Northern Greenland. A key factor in determining when and where ice-shelf estuaries form is river incision rate – the decrease in channel bed elevation over time. Here we present a novel method for calculating incision rate in supraglacial rivers from paired multispectral WorldView imagery and corresponding ArcticDEM strips, applied over Petermann Ice Shelf during the 2014 and 2016 melt seasons. Incision rates differ substantially between the two years, peaking near the river/estuary mouth in 2014, and reaching a minimum there in 2016. Based on visual interpretation of WorldView imagery and modelled runoff from 2013–2018, we conclude these contrasting incision patterns are caused by the formation of the estuary and resultant flow reversal which shifts the dominant melt pattern from vertical incision to lateral erosion. Further, our analysis reveals a cyclical pattern of estuary formation starting in 2014, with the estuary disappearing and reforming annually; this pattern is interrupted in 2018, when a transverse rift bisects the channel. This indicates that estuary presence, even when spatially and temporally limited, may contribute to ice-shelf instability.