Importance of the area of research concerned:
Grounding lines mark the boundary between the grounded ice sheet and floating ice shelves. Grounding line location is a critical indicator of ice sheet imbalance and stability. Even small changes in ice flow or ice thickness at the grounding line can directly alter the rate of ice loss from the ice sheet, impacting the overall Antarctic contribution to sea level rise. In West Antarctica, a region situated on an inherently unstable retrograde bed slope where high rates of ice loss have been driven by warm ocean waters, satellite observations show that grounding lines have retreated at a rate of over one kilometre per year.1
On top of this sustained dynamic retreat, there is also a poorly documented short-term variability caused by ocean tides temporarily lifting the grounded ice off the bed. This tidal migration can be up to several kilometres over a few hours and can obscure the long-term behaviour. It is also thought to increase overall glacier velocity through reduced drag at the bed.2
This project offers an exciting opportunity to work at the interface of climate and space science, making an important contribution to international efforts to study the effects and impact of climate change. In this PhD, you will work closely with world-leading Earth observation experts to better understand change on the Antarctic Ice Sheet. Whilst it is impossible to make a direct observation of the ice-bed interface beneath the ice sheet surface, the grounding line position can be monitored using satellite remote sensing by measuring vertical displacement of the floating ice shelf caused by ocean tides3. This project will make use of ICESat-2 laser altimetry data to map present day change in the grounding line position, monitor stability of the most vulnerable sectors of the Antarctic ice sheet, and investigate how migration driven by ocean tides impacts ice behaviour. The ICESat-2 satellite launched in 2018, and provides unprecedented spatial resolution and coverage of Antarctica. Its laser altimeter is split into six beams transmitting at 10 kHz, which allows a pulse of light to hit the ice sheet surface every 70 cm. The satellite has been specifically designed to allow accurate measurement of cross-track slopes in regions of steep topography (i.e. near grounding lines). These altimetry measurements will be complimented by synthetic aperture radar interferometric measurements of the grounding line location from other satellites including Sentinel-1 and TerraSAR-X.
Harnessing the capability of both historical and new satellite missions, and focusing on one of the most sensitive parts of the ice sheet, the project will provide new insight into fundamental processes driving velocity variation in Antarctic ice shelves and allow current rates of grounding line retreat to be observed with higher confidence.
What will the student do?
The student will analyze new laser altimetry data from ICESat-2 spanning the period from 2018 onwards, building on grounding line mapping studies from previous altimeters (ICESat and Cryosat-2). Radar interferometry and ICESat (2003-2009) will be used to identify long-term change in the grounding line location, while repeat ICESat-2 measurements will be used to identify short-term variability. Horizontal movement of the grounding line will be correlated with ocean tide models to identify how grounding line migration is related to tidal amplitude, local ice properties and bed slope.
We are looking for a highly motivated candidate with strong computing skills and a background in natural/physical sciences or remote sensing. All the students will receive intensive training (12 weeks) in advanced Earth Observation and data analytical techniques for the first year (https://eo-cdt.org/programme/).
1 Konrad, H., Shepherd, A., Gilbert, L., Hogg, A.E., MacMillan, M., Muir, A. and Slater, T. (2018), Net retreat of Antarctic glacier grounding lines, Nature Geoscience, 11, 258-262, doi: 10.1038/s41561-018-0082-z
2 Robel, A. A., Tsai, V. C., Minchew, B., and Simons, M. (2017), Tidal modulation of ice shelf buttressing stresses, Annals of Glaciology, 58, 12-20, doi: 10.1017/aog.2017.22
3 Fricker, H. A. and Padman, L., (2006), Ice shelf grounding zone structure from ICESat laser altimetry, Geophysical Research Letters, 33 (15), doi: 10.1029/2006GL026907