Ocean gravity waves are dynamic elements of the global ocean environment, affected by ocean warming and changes in ocean and atmospheric circulation patterns. Their evolution may thus drive changes in ice-shelf stability by both mechanical interactions, and potentially increased basal melting, which in turn feed back on sea level rise. Our proposed research is intended to discover, through field observations and numerical simulations, how ocean wave-induced vibrations on ice shelves in general, and the Ross Ice Shelf (RIS), in particular, can be used to infer spatial and temporal variability of (1) ice shelf mechanical properties, (2) bulk elastic properties from signal propagation characteristics, and (3) to determine whether the RIS response to IG wave forcing (generated distant from the front) propagates as stress waves from the front or is “locally” generated by IG wave energy penetrating the RIS cavity. Signal propagation across ice shelves depends on ice shelf and sub-shelf water cavity geometry as well as ice shelf physical properties (e.g. structure, thickness, crevasse density and orientation). Emphasis will be placed on observation and modeling of the RIS response to IG wave forcing at periods from 75 to 300 s, as these waves constitute a potentially significant and deeply penetrating forcing mechanism contributing to rift expansion and potentially to ice shelf fragmentation. Because IG waves are not appreciably damped by sea ice, seasonal monitoring will give insights into the year-round RIS response to this oceanographic forcing, as well as provide a 2014-2016 baseline for RIS elastic and anelastic properties. As feasible, these results will be compared with existing data from the Amery Ice Shelf and existing and future data from the RIS.
Field Work and Modeling: The 3-year project will involve a 24-month period of field observation (continuous data collection) spanning a full annual cycle on the RIS. RIS ice-front array coverage overlaps with a synergistic West Antarctic earth structure proposal (Wiens/Aster et al. (2011), giving an expanded array beneficial for IG wave localization. The ice-shelf deployment will consist of sixteen stations equipped with broadband seismometers and barometers. Three seismic stations near the RIS front will provide reference response/forcing functions, and measure the variability of the response across the front. A linear seismic array orthogonal to the front will consist of three stations inline with three Wiens et al. (2011) stations, with the remaining 9 stations clustered in a higher density array near the intersection of the Wiens et al. (2011) transverse linear array and the orthogonal array. Full-year instrument operation will be incorporated in the IRIS PASSCAL-supplied seismographic instrument package. Time-domain finite-difference numerical modeling will be conducted to (a) optimize the field instrument deployment configuration, and (b) to explore theoretical aspects of gravity wave-induced signal propagation in ice shelves, ranging from swell to IG waves. Passive seismic array monitoring will be used to determine the spatial and temporal distribution of ocean wave-induced signal sources along the front of the RIS, estimate ice shelf structure, and to localize fracture (icequake) events.