Observations of tidal melt and vertical strain at the Filchner‐Ronne Ice Shelf, Antarctica

The Filchner‐Ronne Ice Shelf experiences strong tidal forcing known to displace portions of the ice shelf by several meters over a tidal cycle. These large periodic displacements may cause significant variation of the ice shelf vertical strain. Further, tidal currents in the ice shelf cavity may be responsible for basal melt variations. We deployed autonomous phase‐sensitive radio‐echo sounders at 17 locations across the ice shelf and measured basal motion and internal vertical ice motion at sufficiently short intervals to allow the resolution of all significant tidal constituents. Basal melt estimates with this surface‐based technique rely on accurate estimation of vertical strain changes in the ice shelf. We present a method that can separate the vertical strain changes from the total thickness changes at tidal time scales, yielding a tidal basal melt estimate. The method was used to identify vertical strain and basal melt variations at the predominant semi‐diurnal M2 tidal constituent. At most sites the tidal vertical strain was depth‐independent. Tidal deformation at four sites was controlled by local effects causing elastic bending. Significant tidal melt was observed to occur at six locations and upper bounds on the tidal melt amplitude were derived for the remaining sites. Finally, we show that observations of basal melt spectra, specifically at tidal frequencies and their multiples, can provide constraints on the hydrographic conditions near the ice base, such as the non‐tidal background ocean flow.

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