Patterns and drivers of seasonal land-ice-flow around Antarctica

Three decades of satellite remote sensing have documented the multi-annual acceleration of the Antarctic Ice Sheet, and the associated increase in its contribution to global sea level. Unlike the Greenland Ice Sheet, where ice velocity signals are well resolved over both inter- and intra-annual timescales, observations of seasonal signals are limited over the grounded ice in Antarctica. Assessing the degree of seasonal ice-flow variability, and establishing a process-based understanding of the key environmental drivers responsible, are of critical importance for quantifying accurately the total volume of ice discharged from the Antarctic Ice Sheet, and thus its overall contribution to global sea level. Using an array of remotely sensed, modelled and reanalysis datasets, this thesis aims to identify land-ice-flow seasonality in Antarctica for the first time, and to establish the key atmosphere-ocean-ice interactions responsible. First, high-spatial- and high-temporal-resolution Copernicus Sentinel-1A/B synthetic aperture radar observations acquired between 2014 and 2020 are used to provide the first evidence for seasonal flow variability of the land ice feeding George VI Ice Shelf, Antarctic Peninsula. The observations reveal a distinct austral summertime (December – February) speed-up of ∼0.06 ± 0.005 m d⁻¹ (∼22 ± 1.8 m yr⁻¹) at, and immediately inland of, the grounding line of the glaciers nourishing the ice shelf, which constitutes a mean acceleration of ∼15 % relative to baseline (time-series-averaged) rates of flow. These findings are corroborated by independent, optically derived velocity observations obtained from Landsat 8 imagery. Second, time-series analysis is performed on an array of remotely sensed, modelled and reanalysis datasets to examine the influence of potential environmental forcing mechanisms upon ice-flow seasonality at George VI Ice Shelf. Both meltwater presence and ocean temperature are shown to act as statistically significant precursors to summertime ice-flow acceleration, although each elicit an ice-velocity response after a distinct lag, with the former prompting a more immediate response. Furthermore, the timing and magnitude of these local drivers are found to be influenced by large-scale climate phenomena, namely the Amundsen Sea Low and the El Niño Southern Oscillation, with the latter initiating an anomalous wintertime ice-flow acceleration event in 2016. Finally, a continental-scale analysis of a 7-year SAR-derived velocity record is presented which reveals that 60% of Antarctica’s routinely monitored drainage basins are subject to ice-flow seasonality. Using statistical time-series analysis, this seasonality is attributed to a combination of surface-, oceanic- and sea ice-forcing mechanisms impinging upon the continent, although the relative importance of each, and the nature of the interactivity, varies along the coast.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• Boxall, Karla

Advisors dc:contributor.advisor

• Willis, Ian
• Christie, Frazer

• Antarctic Ice Sheet
• Seasonal
• Ice velocity
• Synthetic Aperture Radar

Licence

• https://www.repository.cam.ac.uk/bitstreams/622410e8-7bfe-4747-8b5f-8e272fff66a6/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

Author Identifier

0000-0002-6574-7717

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/381241