Grounding line migration and high‐resolution calving dynamics of Jakobshavn Isbræ, West Greenland

Abstract

[1] We performed three field campaigns in 2004, 2007, and 2010 at the southern margin of the Jakobshavn Isbrae, West Greenland, in order to infer flow velocities and their changes from photogrammetric time-lapse imagery with a temporal resolution of 20 min and a spatial spacing of about 30 m on the glacier surface. Area-wide analysis of more than 3000 three-dimensional trajectories at individual glacier positions allow for both the mapping of the grounding line and the detailed observation of flow variations during major calving events. From 2004 to 2010, the grounding line of Jakobshavn Isbrae retreated 3.5 AE 0.2 km. Considering previously published results, the grounding line retreat amounts to 6 km since 1985. The glacier has an ephemeral floating tongue that can establish during the readvance of the glacier front and break apart after large calving events. Observations of a major calving event show that an acceleration of flow velocities coincides with the onset of the break up during which flow velocities of up to 70 m/d can be reached. Moreover, large vertical displacements of the glacier front in the order of 15 m and lowering of 8 m at positions 500 m beyond the calving front were observed 2 days before the calving event.After the break up, the glacier slowly adjusts to the new boundary conditions within the next 4-5 days. Flow velocity variations caused by calving were detected up to 1 km upstream only which indicates that individual calving events have no immediate effect on the large-scale glacier dynamics.

Glacier Calving in Greenland

“…Buoyancy-driven calving is an important process on large, fast-flowing outlet glaciers [59][60][61][62][63][64]. Rapid ice flow into deep water can create 'super-buoyant' conditions, in which ice fronts are out of hydrostatic equilibrium and subject to large upward-directed torque forces (Fig.…”

The determination of high-resolution spatio-temporal glacier motion fields from time-lapse sequences

“…The presented approach has been developed in the course of several glacier measurement projects between 2004(e.g. Dietrich et al, 2007Rosenau et al, 2013;Schwalbe et al, 2016). This paper has the aim of integrating the experiences gained from these projects.…”

Grounding line migration through the calving season of Jakobshavn Isbræ, Greenland, observed with terrestrial radar interferometry

“…S6 and S7. Previous studies indicate that apart from calving events, short-term ice velocity variations at Jakobshavn Isbrae are well described with simple tidal response models (e.g., Rosenau et al, 2013;Podrasky et al, 2014). Diurnal variation caused by surface melting may also contribute to velocity variation.…”

“…However, some basal conditions, such as grounding line position, can be inferred from measured ice motion (Heinert Riedel, 2007;Rignot et 15 al., 2011;Rosenau et al, 2013). It has been observed that for many marine-terminating glaciers, ice speed is affected by ocean tides (e.g., Makinson et al, 2012;Podrasky et al, 2014;Voytenko et al, 2015a).…”

“…Based on the fast decay of tidal responses 20 upstream, they concluded that the terminus region is very nearly grounded during summer months. Rosenau et al (2013) used photogrammetric time-lapse imagery to estimate groundling line migration and calving dynamics at Jakobshavn Isbrae. They found that the groundling line retreated 3.5 km from 2004 to 2010, with an ephemeral floating tongue during the advance season.…”