The control of short-term ice mélange weakening episodes on calving activity at major Greenland outlet glaciers

• Main Authors: Wehrlé, Adrien, Lüthi, Martin P., Vieli, Andreas
• Format: Text
• Language: English
• Published: 2023
• Subjects: Greenland; Jakobshavn Isbræ; Kujalleq; glacier; greenlandic; Jakobshavn; Jakobshavn isbræ; Kangia; Sea ice; Sermeq Kujalleq; Tidewater
• Online Access: https://doi.org/10.5194/egusphere-2022-805; https://egusphere.copernicus.org/preprints/2022/egusphere-2022-805/

The dense mixture of iceberg of various sizes and sea ice observed in many of Greenland's fjords, called ice mélange ( sikussak in Greenlandic), has been shown to have a significant impact on the dynamics of several Greenland tidewater glaciers, mainly through the seasonal support it provides to the glacier terminus in winter. However, a clear understanding of shorter-term ice mélange dynamics is still lacking, mainly due to the high complexity and variability of the processes at play at the ice–ocean boundary. In this study, we use a combination of Sentinel-1 radar and Sentinel-2 optical satellite imagery to investigate in detail intra-seasonal ice mélange dynamics and its link to calving activity at three major outlet glaciers: Kangerdlugssuaq Glacier, Helheim Glacier and Sermeq Kujalleq in Kangia (Jakobshavn Isbræ). In those fjords, we identified recurrent ice mélange weakening (IMW) episodes consisting of the up-fjord propagation of a discontinuity between jam-packed and weaker ice mélange towards the glacier terminus. At a late stage, i.e., when the IMW front approaches the glacier terminus, these episodes were often correlated with the occurrence of large-scale calving events. The IMW process is particularly visible at the front of Kangerdlugssuaq Glacier and presents a cyclic behavior, such that we further analyzed IMW dynamics during the June–November period from 2018 to 2021 at this location. Throughout this period, we detected 30 IMW episodes with a recurrence time of 24 d, propagating over a median distance of 5.9 km and for 17 d, resulting in a median propagation speed of 400 m d −1 . We found that 87 % of the IMW episodes occurred prior to a calving event visible in spaceborne observations and that ∼75 % of all detected calving events were preceded by an IMW episode. These results therefore present the IMW process as a clear control on the calving activity of Kangerdlugssuaq Glacier. Finally, using a simple numerical model for ice mélange motion, we showed that a slightly biased random motion of ice ...