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Mapping Antarctica's Subglacial Lakes from Space

Dr. Malcolm McMillan (SEE), Prof. Andrew Shepherd (SEE)

Contact email: m.mcmillan@leeds.ac.uk

Hidden beneath the Antarctic Ice Sheet lies a vast network of subglacial lakes (Smith et al., 2009). Recent satellite surveys have revealed that, far from being stable, many of these lakes fill and drain rapidly, causing massive subglacial floods beneath the ice sheet and the sudden discharge of freshwater into the ocean (Fricker et al., 2007; McMillan et al., 2013; Flament et al., 2014).

Our present understanding of this remote and inaccessible hydrological system is, however, still in its infancy. What triggers these lake to drain? How do they affect the overlying ice? And what is their impact upon ocean circulation? These questions remain unanswered because we lack sufficient observations to systematically monitor lake evolution. As a result, one of primary influences on ice sheet dynamics, that of subglacial hydrology, remains poorly understood (Carter et al., 2011), and models that simulate ice sheet evolution lack key physical information.

Figure 1. Top. A 70 m crater in the surface of the Antarctic Ice sheet, which formed recently when 6 billion tonnes of water drained from an underlying subglacial lake, (McMillan et al., 2013). Bottom. Schematic showing the impact of subglacial lake filling and drainage on ice surface elevation (credit Nature Publishing Group).

Mapping the evolution of subglacial lakes can therefore improve our understanding of the processes driving ice sheet change, and the interaction of ice sheets with the wider climate system. Determining the rate at which lakes fill can be used to constrain geothermal heat flux beneath the ice sheet (Pattyn, 2010); monitoring the rate at which they drain will shed new light on interactions between the subglacial and ocean environments (Carter and Fricker, 2012).

Because lakes are hidden beneath several kilometers of ice, systematically monitoring their behaviour is challenging. In recent years, however, satellite based techniques have been developed, which track the imprint that subglacial lakes leave upon the overlying ice surface; observing the rise and fall of the ice sheet as the underlying lake fills and drains (Figure 2). This technique has been successfully applied to satellite laser altimetry data to produce an Antarctic inventory of active subglacial lakes (Smith et al., 2009) but has yet to be developed for radar altimetry, which although more challenging, offers greater potential to develop long-term records of lake evolution.

This project aims to use satellite altimetry to map changes in ice surface elevation above active subglacial lakes. Particular focus will be on the utilisation of the new generation of high resolution Synthetic Aperture Radar altimeters, including CryoSat-2 and Sentinel-3. As such, the project will work with state-of-the-art satellite data which utilizes the most recent advances in instrument and processing methods. The project would suit a numerate candidate with a degree in a discipline such as Physics, Mathematics, Engineering, Earth Sciences, Geography or Computer Sciences.

Objectives

In this project, you will work as part of a team of Polar Earth Observation scientists at Leeds, within the UK Centre for Polar Observation and Modelling. This project will focus on utilising past, present and future satellite altimeter missions to:

  1. Develop and test methods for mapping ice surface elevation change above subglacial lakes using state-of-the-art satellite data processing techniques.

  2. Produce an Antarctic-wide map of currently active subglacial lakes and compute water transfer beneath the ice sheet.

  3. Explore the potential of high resolution measurements from the new Sentinel-3 satellite, launched at the beginning of 2016, to identify and monitor subglacial lakes.

Figure 2. Evolution of the Antarctic Ice Sheet surface above active subglacial lakes, mapped by satellite altimetry (Siegfried et al., 2014).

Potential for high impact outcome

Understanding and monitoring current changes to Earth’s ice sheets is of global significance. Their health; whether they are contributing or removing water from the oceans, directly affects the global climate system, impacting upon present rates of sea level rise and many coastal communities. Understanding how ice sheets evolve, and in particular the influence of the subglacial system upon the overlying ice, is critical to developing realistic physical models of ice sheet evolution and reliable projections of future sea level rise. This project has the potential to produce the most comprehensive observational analysis of Antarctic subglacial behaviour, using the latest satellite data. We therefore anticipate that the work will lead to several publications, with at least one submission to a high impact journal.

Training

The successful candidate will work under the supervision of Dr. Malcolm McMillan and Prof. Andrew Shepherd within the ICAS Polar Earth Observation group. The group, which currently includes 2 PhD students and 4 postdoctoral researchers, offers a supportive and collaborative environment for training as a polar Earth Observation scientist. The project will provide specialist training in geodetic Earth Observation techniques, algorithm development and data processing. The student will also benefit from being a member of the UK Centre for Polar Observation and Modelling, a national research centre that brings together researchers from the universities of Leeds, UCL, Bristol and Reading, and has over twenty years of experience of satellite radar altimetry design, development and data processing.

The successful PhD student will have access to a broad spectrum of training workshops put on by the Faculty, including computer programming, degree management and communication (http://www.emeskillstraining.leeds.ac.uk/).

References

Carter, S. P., And H. A. Fricker (2012), The Supply of subglacial meltwater to the grounding line of   the Siple Coast, West Antarctica, Annals of Glaciology, 53(60), 267‐280.

Carter, S. P., H. A. Fricker, D. D. Blankenship, J. V. Johnson, W. H. Lipscomb, S. F. Price, and D. A. Young (2011), Modeling 5 years of subglacial lake activity in the MacAyeal Ice Stream (Antarctica) catchment through assimilation of ICESat laser altimetry, Journal of Glaciology, 57 (206), 1098–1112.

Flament, T., E. Berthier, and F. Remy (2014), Cascading water underneath Wilkes Land, East Antarctic ice sheet, observed using altimetry and digital elevation models, The Cryosphere 8, 673-687.

Fricker, H. A., T. Scambos, R. Bindschadler, and L. Padman (2007), An active subglacial water system in West Antarctica mapped from space, Science, 315(5818), 1544–1548, doi:10.1126/science.1136897.

McMillan, M., H. Corr, A. Shepherd, A. Ridout, S. Laxon, and R. Cullen (2013), Three-dimensional mapping by CryoSat-2 of subglacial lake volume changes, Geophys. Res. Lett., 40, doi:10.1002/grl.50689.

Pattyn, F. (2010), Antarctic subglacial conditions inferred from a hybrid ice sheet/ice stream model, Earth and Planetary Science Letters, 295(3-4), 451–461, doi:10.1016/j.epsl.2010.04.025.

Siegfried, M. R., H. A. Fricker, M. Roberts, T. A. Scambos, and S. Tulaczyk (2014), A decade of West Antarctic subglacial lake interactions from combined ICESat and CryoSat-2 altimetry, Geophys. Res. Lett., 41, doi:10.1002/2013GL058616.

Smith, B., H. A. Fricker, I. Joughin, and S. Tulaczyk (2009), An inventory of active subglacial lakes in Antarctica detected by ICESat (2003-2008), Journal of Glaciology, 55(192), 573–595.

Related undergraduate subjects:

  • Computer science
  • Earth science
  • Engineering
  • Geography
  • Mathematics
  • Physics