Tidally induced variations in vertical and horizontal motion on Rutford Ice Stream, West Antarctica, inferred from remotely sensed observations
To better understand the influence of stress changes over floating ice shelves on grounded ice streams, we develop a Bayesian method for inferring time-dependent 3-D surface velocity fields from synthetic aperture radar (SAR) and optical remote sensing data. Our specific goal is to observe ocean tide-induced variability in vertical ice shelf position and horizontal ice stream flow. Thus, we consider the special case where observed surface displacement at a given location can be defined by a 3-D secular velocity vector, a family of 3-D sinusoidal functions, and a correction to the digital elevation model used to process the SAR data. Using nearly 9 months of SAR data collected from multiple satellite viewing geometries with the COSMO-SkyMed 4-satellite constellation, we infer the spatiotemporal response of Rutford Ice Stream, West Antarctica, to ocean tidal forcing. Consistent with expected tidal uplift, inferred vertical motion over the ice shelf is dominated by semidiurnal and diurnal tidal constituents. Horizontal ice flow variability, on the other hand, occurs primarily at the fortnightly spring-neap tidal period (M_(sf)). We propose that periodic grounding of the ice shelf is the primary mechanism for translating vertical tidal motion into horizontal flow variability, causing ice flow to accelerate first and most strongly over the ice shelf. Flow variations then propagate through the grounded ice stream at a mean rate of ∼29 km/d and decay quasi-linearly with distance over ∼85 km upstream of the grounding zone.
Additional Information© 2016. American Geophysical Union. Issue online: 17 February 2017; Version of record online: 13 January 2017; Accepted manuscript online: 22 November 2016; Manuscript Accepted: 18 November 2016; Manuscript Revised: 5 October 2016; Manuscript Received: 27 May 2016. We thank E. Smith and A. Smith for providing the seismic data and we benefitted from conversations with H. Gudmundsson, H. Martens, V. Tsai, J.Thompson, and P. Agram. B.M. was partially funded by NASA Cyospheric Sciences award NNX14AH80G, NSF Earth Sciences Postdoctoral Fellowship award 1452587, and donations from the Albert Parvin and ARCS LA Chapter foundations. B.R. was partially funded by a NASA Earth and Space Sciences fellowship. P.M. was partially funded by a NASA postdoctoral fellowship and much of this work was completed while he was a visiting student at the California Institute of Technology. Original COSMO-SkyMed products (copyright ASI -Agenzia Spaziale Italiana, 2013–2016) are archived at JPL and were processed under license from ASI as part of a collaborative project between CIDOT and JPL/Caltech. Displacement fields and other processed SAR data are available from the authors upon request and the velocity field components will be archived at the National Snow and Ice Data Center (NSIDC; see nsidc.org). Software used to infer time-dependent,3D velocity fields is freely available at https://github.com/bminchew/fourDvel.
Supplemental Material - JGRF.sup-1.pdf