Abstract
ABSTRACTOn 2 March 2016, several small en échelon tabular icebergs calved from the seaward front of the McMurdo Ice Shelf, and a previously inactive rift widened and propagated by ~3 km, ~25% of its previous length, setting the stage for the future calving of a ~14 km2 iceberg. Within 24 h of these events, all remaining land-fast sea ice that had been stabilizing the ice shelf broke-up. The events were witnessed by time-lapse cameras at nearby Scott Base, and put into context using nearby seismic and automatic weather station data, satellite imagery and subsequent ground observation. Although the exact trigger of calving and rifting cannot be identified definitively, seismic records reveal superimposed sets of both long-period (>10 s) sea swell propagating into McMurdo Sound from storm sources beyond Antarctica, and high-energy, locally-sourced, short-period (<10 s) sea swell, in the 4 days before the fast ice break-up and associated ice-shelf calving and rifting. This suggests that sea swell should be studied further as a proximal cause of ice-shelf calving and rifting; if proven, it suggests that ice-shelf stability is tele-connected with far-field storm conditions at lower latitudes, adding a global dimension to the physics of ice-shelf break-up.
Highlights
Interest in the brittle behaviour of ice shelves leading to fracture, iceberg calving and even disintegration, presents a challenging observational task because the tangible effects of fracture and calving are often difficult to discover until long after they occur
Of all the environmental conditions documented prior to the calving/rifting event, the one that shows the greatest change around the time of the event is the high-energy sea swell recorded by the SBA seismometer and the cameras looking at the sea ice along the shoreline of Scott Base
The purpose of this work has been to document the calving/ rifting event that occurred on 2 March 2016 on the McM Ice Shelf using both routine seismic, weather and satellite data, as well as data gleaned from various ground-based cameras and survey
Summary
Interest in the brittle behaviour of ice shelves leading to fracture, iceberg calving and even disintegration, presents a challenging observational task because the tangible effects of fracture and calving are often difficult to discover until long after they occur. Examples of observational studies addressing ice-shelf brittle behaviour include the multi-year view of rifting on Pine Island Glacier and the Amundson Sea coast (MacGregor and others, 2012; Jeong and others, 2016), the study of rifting and calving on the Ross Ice Shelf leading to iceberg C19 (Joughin and MacAyeal, 2005) and study of the ‘loose tooth’ rift system on the Amery Ice Shelf (Bassis and others, 2008; Walker and others, 2013, 2015) Extremely valuable, these previous studies exemplify that typically only one observational system (e.g., a satellite remotesensing platform) is involved in recording the rifting/calving process, meaning that it has often been hard to pin down the exact timing and potential cause(s) of the events. The goals of this study are to present this context and to seek the cause of the calving and rifting event so as to better inform similar studies in the future
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