Grounding Zone Measurements from Spaceborne Interferometric SAR as a Crucial Descriptor of the Ice Ocean Interface of Glaciers

The ice - ocean interface of a glacier is a critical boundary described by the grounding line, which delineates where ice detaches from the bed and becomes afloat and frictionless at its base [3]. We use synthetic aperture radar (SAR) double difference interferometry to measure the grounding line position. With support from the NASA MEaSUREs program, we produce an Earth System Data Record (ESDR) that is archived at the National Snow and Ice Data Center (NSIDC). The European Union Sentinel-1 mission now regularly collects data suitable for grounding line detection in coastal Antarctica [4] and the Italian Space Agency COSMO SkyMed constellation contributes with short repeat acquisitions over fast glaciers. This increase in data availability provides many grounding line delineations over the course of a year [2]. The wealth of data now available shows a variation of the grounding line position at tidal frequencies. This variation is typically 10 times wider than expected from hydrostatic equilibrium [1]. We define the grounding zone of as the full range of variability of grounding line positions and present an Antarctica-wide grounding zones based on Sentinel-1, COSMO SkyMed, and other spaceborne SAR missions. We highlight the need for continued data acquisitions, identify areas where improvements are needed, and make recommendations for acquisition plan coordination based on current and upcoming SAR mission capabilities. The grounding zone is an expansion of the grounding line ESDR and is a crucial element for the interpretation of glacier dynamics. We compare the grounding zone with grounding lines from previous years and identify a number of spectacular changes around Antarctica, some of which have not been widely publicized. The broad and widespread intrusion of seawater at tidal frequencies has vast implications for the modeling of glacier dynamics, as anticipated by a number of pioneer studies who considered the possibility of high melt at the grounding line. This work is funded by NASA MEaSUREs program.

[1] Milillo et al., (2017).

https://doi.org/10.1002/2017GL074320

[2] Mohajerani, et al. (2021).

https://doi.org/10.1038/s41598-021-84309-3

[3] Rignot et al. (2014).

https://doi.org/10.1002/2014GL060140

[4] Scheuchl et al. (2016).

https://doi.org/10.1002/2016GL069287