Ice shelves buttress ice sheets on land, restraining ice sheet movement towards the ocean. Ice shelves and ice shelf fragments are appreciably (and constantly), flexed, rocked, rolled, pitched, elongated and compressed by various components of ocean waves. Recent theory and observations indicate that a better understanding of ice-shelf/ocean-wave interactions can lead to a better prediction of ice-shelf response to a changing environment, that includes increased storminess and related ocean-wave effects (Bromirski et al., 2005a; Bromirski et al., 2003). Gravity wave impacts could significantly affect ice shelf rift propagation, crevasse expansion, and other pre-existing fractures, affecting ice shelf stability. The collapse of ice shelves allows ice sheets on land to flow faster to the ocean, raising sea level. The response of ice shelves to gravity wave impacts and ice shelf properties can be estimated from seismometer data recorded on ice shelves.
Ocean waves impacting the Ross Ice Shelf (RIS) originate in the North Pacific (e.g. path c in Figure 1) as well as in the Southern Ocean surrounding Antarctica (Bromirski et al., 2010). North Pacific swell (10-30s period) is transformed along coasts to very long period (50-300s) infragravity (IG) waves. The IG waves propagate to Antarctic along paths a and b. Ice shelves respond to wave impacts at characteristic frequencies, depending on ice shelf thickness and water depth below the floating shelf (Bromirski and Stephen, 2012).
Spectral characteristics (Figure 2) of the response of the RIS to gravity wave impacts (recorded by a seismometer at N) allow determination of their generation location. The wave impact signal at the RIS from the extreme North Pacific wave event (path c in Fig. 1; circled in black in Fig. 2) occurs during the Antarctic summer, when sea ice (that damps ocean wave energy) is at a minimum. The sea ice damping effect (exhibited by the much lower spectral levels within the white circled region in Fig. 2) is most pronounced during the Antarctic winter when Southern ocean storms are strongest. So North Pacific waves may have a greater impact on the RIS than waves generated locally.