Melting and deformation of the Ross Ice Shelf, Antarctica, by Multi-Year Phase Sensitive Radio Echo Sounding
Antarctic ice shelves are an important part of the Antarctic ice sheet system, holding back the grounded ice front from accelerating onto the ocean and contributing to sea level rise. As ice shelves float on the ocean, they are the most vulnerable to oceanic and environmental changes. The oceans in...
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| Format: | Other/Unknown Material |
| Language: | English |
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University of Canterbury
2021
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| Online Access: | https://dx.doi.org/10.26021/11366 https://ir.canterbury.ac.nz/handle/10092/102317 |
| Summary: | Antarctic ice shelves are an important part of the Antarctic ice sheet system, holding back the grounded ice front from accelerating onto the ocean and contributing to sea level rise. As ice shelves float on the ocean, they are the most vulnerable to oceanic and environmental changes. The oceans in the ice shelf cavity remain some of the most unexplored places in the world with only a few observations. The Ross Ice Shelf is the largest ice shelf in the world, buttressing 11.6m of potential sea level rise within its catchment. This study presents the first precision Autonomous Phase-sensitive Radio Echo Sounding (ApRES) measurements of ice shelf thickness, internal deformation and basal melting across an entire traverse of the Ross Ice Shelf. Autonomous Phase-sensitive Radio Echo Sounding (ApRES) is a ground-based instrument that can record reflections of internal layers and the ice shelf base to millimetre precision using phase-based measurements. The ice shelf thickness change and internal deformation are used to determine basal melting. Phase coherence of stable internal and basal reflectors over the survey period allows this type of analysis. Up to 5 seasons of annual ApRES measurements were collected at 32 locations along the South Pole Overland Traverse (SPOT) and Siple Coast Traverse (SCT). The survey covered a 1000km transect of the Ross Ice Shelf (RIS) from Mina Bluff to the Kamb Ice Stream (KIS). Strong basal reflection strength in the north and southern regions indicated well-defined ice-ocean interfaces formed from basal melting. Weaker reflections and lower apparent thickness across the central RIS sites indicated the presence of marine ice or debris. Basal melting was 0-0.02 m a-1 for a large area of the central RIS, with data gaps where marine ice and debris are present. Basal melting rises to 0.25-0.45 m a-1 at the southern and northern ends of this region due to the expected influence of High Salinity Shelf Water (HSSW) and Antarctic Surface Water (AASW) respectively. Basal melt rates of 0.01-0.04 m a-1 were consistent across the Siple Coast study area and reached 0.14 m a-1 within 11km of the KIS grounding zone. With increasing distance downstream from the KIS and WIS, the basal melting rate decreased and the strain thinning rate increased as the ice shelf continued to thin. Remote sensing observations of basal melting must account for the dynamic thinning component of the total ice shelf thickness change. The MEaSUREs satellite velocity datasets were used with strain processing scripts from Alley et al. (2018) to calculate vertical strain deformation across the study area. The satellite-derived strain rates correlated well with the ApRES ground based strain rates, supporting the accuracy of current remote sensing deformation methods and basal mass balance studies. The ApRES basal melt rates showed similar patterns to those from remote sensing and ocean modelling but were generally smaller and less spatially variable. This indicates the RIS is maintaining steady state basal mass rates across its interior. The spatial variability suggests there remains inaccuracies and uncertainties for remote sensing studies, possibly due to the accumulation models, that could be addressed by future ApRES or climate studies. |
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