| Summary: | Antarctic ice shelves play a key role in regulating the rate of flow in tributary ice streams. Temporal variations in the associated ice-shelf buttressing stress are observed to impact the flow in glaciers and ice streams. Ephemeral grounding induced by tides is considered as an important mechanism for modulating the buttressing stress. Here, we develop an approach to inferring variations in 3-D surface displacements at an ice-shelf-stream system that explicitly accounts for ephemeral grounding. Using a temporally dense 9-month long SAR image acquisition campaign collected over Rutford Ice Stream by the COSMO-SkyMed 4-satellite constellation, we infer the ephemeral grounding zones and the spatial-temporal variation of the fortnightly flow variability. Expanding on previous results, we find ephemeral grounding zones along the western ice-shelf margin as well as a few prominent ephemeral grounding points in the central trunk and in the vicinity of the grounding zone. Our observations provide evidence for tide-modulated buttressing stress and the temporally asymmetric response of ice-shelf flow to tidal forcing. Our study suggests that RIS will accelerate if the ice shelf thins sufficiently that the ephemeral grounding zones we have identified remain permanently ungrounded over the tidal cycle. We thank ASI for their efforts in making the observational campaign at Rutford Ice Stream1003successful and the SAR data available. We thank Andrew F. Thompson for providing helpful1004suggestions on revising the manuscript. B.M. acknowledges NSF-NERC awards 1853918 and10051739031 Open Research. The velocity and displacement field components (Zhong et al., 2022) are archived at https://zenodo.org/record/6615587#.Yp1DbGDMLao. Software used to perform feature tracking on SAR images (Zhu et al., 2022) is freely available at https://github.com/lijun99/cuAmpcor. Software used to infer ephemeral grounding (Zhong & Simons, 2022) is freely available at https://github.com/mzzhong/fourDvel2. Submitted - essoar.10511631.1.pdf ...
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