IAP2-23-077

(How) does active basal hydrology influence the onset of ice stream flow?

Onset zones, where ice flow exceeds ~25 m/yr, are important components of the interior ice sheet, as they often mark the initiation of the fast-flowing ice streams and outlet glaciers that discharge ice into the ocean. Onset zones therefore control ice flow direction and ice sheet flux, and they have the potential to change gradually and abruptly in both the rate of ice flow and their location. Whilst much recent research focus has been on the margin of the Antarctic ice sheet and its ice-ocean interactions, it is vital that we also determine the process glaciology of the interior ice sheet, and how glaciological changes may impact overall ice flux in future.

The onset of enhanced ice sheet flow is thought to be associated with the transition from internal deformation to basal sliding. These ‘onset zones’ are often geographically coincident with ice surface anomalies suggestive of active basal hydrology (i.e. active subglacial lakes). However, few studies have fully evaluated the role of basal hydrology on ice sheet onset zones, and there is often an assumption, at least in Antarctica, that if there is evidence for water, then that water will lubricate the ice sheet bed, resulting in the ice sheet flowing faster. This PhD project will evaluate the impact of basal water in Antarctic ice sheet onset zones, exploring whether basal water causes enhanced ice flow, or whether the enhanced ice flow produces the basal water.

The project will determine the relationship between active basal hydrology and the onset of ice stream flow in the Weddell Sea sector of Antarctica. This area, comprising ice flowing from the Antarctic Peninsula and the West and East Antarctic ice sheets, has a highly active subglacial hydrological system with down-ice impacts. Here, the focus will be on the interior parts of the ice sheet, focusing on how basal water influences the diverse range of major ice streams and types of onset zones in this sector.

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Image Captions

3D view of ice flow in the Weddell Sea sector of Antarctica, showing ice stream flow extending into the interior of the ice sheet. Onset zones are the areas where the colour scheme is transitioning from blue to yellow. Ice velocity data from https://nsidc.org/data/nsidc-0754/versions/1

Methodology

The research methods used in this project are diverse and highly adaptable, with substantive opportunities for the successful candidate to build their own project, tailored to their own interests, within the project’s broad research theme. Three research approaches could be deployed: (i) geophysics to constrain ice sheet glaciology and basal boundary conditions; (ii) remote sensing to observe and quantify basal hydrology and ice flow; and (iii) numerical ice sheet modelling to evaluate how basal water influences ice flow. The supervisory team has been specifically developed to facilitate the deployment of all, or some, of these approaches depending on how the PhD project evolves.

Once an appropriate set of target ice streams from the Weddell Sea sector has been selected, there is opportunity to: (1) undertake an integrated and high-resolution characterisation of the glaciology and basal hydrology of a selection of ice stream onset zones using ice penetrating radar and remote sensing observations of ice sheet surface elevation change (e.g. ICESat2, CryoSat2, Reference Elevation Model of Antarctica (REMA) digital elevation models etc.); (2) evaluate, using a numerical ice sheet model (e.g. Ua or PISM), how basal hydrology may influence the nature and location of ice stream onset zones, and the sensitivity of onset zones to change (e.g. by spatially varying the basal slipperiness, and by looking at how different sliding laws impact ice flow). The modelling could enable the scaling-up of the analysis of specific ice streams to the wider Weddell Sea sector. Geophysical and remote sensing observations will be used as input data to set-up and constrain the numerical model.

This PhD project is timely and low risk because of the convergence of the release of accessible Antarctic-wide ICESat2 and CryoSat2 remote sensing data, REMA surface topography, British Antarctic Survey and Operation IceBridge ice penetrating radar datasets across the Weddell Sea sector, and the upcoming Bedmap3 compilation of ice thickness. All the datasets that will be used in the PhD are already openly available and are now often provided in user-friendly and accessible forms (e.g. Cryo-TEMPO CryoSat-2products). Advances in numerical models also mean that evaluating how basal water and basal slip influence ice flow is achievable within a 3.5 yr PhD project.

Project Timeline

Year 1

Identify target ice stream catchments; Select most appropriate numerical model; Develop coding/big data/remote sensing skills; Develop aims and objectives/research goals; Attend UK conference (e.g. International Glaciological Society British Branch); Undertake training (e.g. Karthaus Summer school on Ice Sheets and Glaciers in the Climate System, appropriate NERC training courses); Spend 1-2 weeks at British Antarctic Survey with 2nd Supervisor Dr Marsh.

Year 2

Quantify ice surface elevation changes (e.g. for 2020-2025) and compare to ice-penetrating radar derived bed topography, subglacial hydrological pathways and basal properties; Evaluate how selected ice stream onset zones function and the controls on their location; Attend UK and international conference (e.g. European Geoscience Union); Write 1st results chapter of PhD; Continue to explore training opportunities (e.g. Úa or other numerical model user meeting). Spend 1-2 weeks at British Antarctic Survey with 2nd Supervisor Dr Marsh.

Year 3

Numerical modelling of target catchment/s with PISM/Úa to evaluate the impact of basal melt and active basal hydrology on ice stream onset zones; Attend international conference (e.g. European Geoscience Union); Write 2nd results chapter of PhD. Spend 1 week at British Antarctic Survey with 2nd Supervisor Dr Marsh.

Year 3.5

Write 3rd results chapter of PhD and submit thesis.

Training
& Skills

There will be numerous opportunities for the successful candidate to develop skills and to undergo training throughout the course of the PhD. This training can be ‘in-house’ as well as via external training (e.g. provided by NERC-funded training courses for PhD researchers, or overseas summer schools such as Karthaus). There are obvious opportunities for developing ‘big data’ skills, i.e. remote sensing, coding, geophysics and numerical modelling, which are highly sought after in both academia and industry. Between them, the supervisory team also have substantial experience in supporting their PhD researchers to undertake training not directly related to the PhD project (e.g. in the form of IAPETUS2 industry placements, UKRI overseas placements, skills training appropriate for work in industry etc.) during their PhDs. We would encourage any new PhD researchers to also explore such opportunities.

References & further reading

Bell, R.E., Studinger, M. Shuman, C.A., et al., (2007). Large subglacial lakes in East Antarctica at the onset of fast-flowing ice streams, Nature, 445, 904-907 https://doi.org/10.1038/nature05554

Bennett, M.R., (2003). Ice streams as the arteries of an ice sheet: their mechanics, stability and significance. Earth Science Reviews, 61, 309-339. https://doi.org/10.1016/S0012-8252(02)00130-7

Diez, A., Matsuoka, K., Jordan, T. A., Kohler, J., Ferraccioli, F., Corr, H. F., et al. (2019). Patchy lakes and topographic origin for fast flow in the Recovery Glacier system, East
Antarctica. Journal of Geophysical Research: Earth Surface, 124. https://doi.org/10.1029/2018JF004799

Dow, C.F., Ross, N., Jeofry, H, Sui, K and Siegert, M.J., (2022). Antarctic basal environment shaped by high-pressure flow through a subglacial river system, Nature Geoscience, 15, 892–898 (2022). https://doi.org/10.1038/s41561-022-01059-1

Grinsted, A., Hvidberg, C.S., Lilien, D.A., Rathmann, N.M., Karlsson, N.B., et al. (2022). Accelerating ice flow at the onset of the Northeast Greenland Ice Stream. Nature Communications, 13, 5589. https://doi.org/10.1038/s41467-022-32999-2

Sanderson, R. J., Winter, K., Callard, S. L., Napoleoni, F., Ross, N., Jordan, T. A., and Bingham, R. G.: Englacial Architecture of Lambert Glacier, East Antarctica, The Cryosphere Discuss. [preprint], https://doi.org/10.5194/tc-2023-13, in review, 2023.

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