Oceanic influence on ice sheet stability

Ocean controlled sedimentation, subglacial water outflow and ice shelf basal melting, influences on ice sheet stability

Degree type

PhD

Closing date

10 October 2022

Campus

Hobart

Citizenship requirement

Domestic/International

About the research project

Antarctica contains the Earth’s largest ice-sheet, which in response to climate warming, may lose ice mass and raise sea level by several metres from the regions grounded below sea level - known as the marine ice sheet.  Much of the threshold behavior of marine ice sheets is thought to result from processes occurring at the grounding zone, where the ice sheet transitions into ice shelves and meets the ocean.  Both glaciological and oceanic processes at grounding zones, which divide floating ice shelves from grounded ice sheets, can strongly influence the dynamics and evolution of inland ice, and therefore control the rate of potential ice loss causing sea level rise under future warming.

The grounding zone is characterised by several influences on the ice flow that include where the basal melting is highest and over hours to weeks is likely influenced by subglacial outflows, and the role of ocean mixing. At timescales from decades to centuries the behavior of the ice sheet at the grounding zone is likely to also be influenced by sediment deposition and bedrock uplift rates due to unloading from the last glacial maximum - called glacial isostatic adjustment. The buildup of sediment at the grounding zone is a poorly understood process that is thought to be due to both glacier erosion of the bedrock when they are advancing, and oceanic sedimentation from subglacial water outflow (e.g. Simkins and others, 2018). Sedimentation processes at the grounding zone are thought to be controlled by the outflow of subglacial water created at the ice sheet base by both basal sliding and geothermal heating.

These geometric controlled feedback between subglacial water outflow, basal melting, and sedimentation processes in the sub-ice-shelf ocean cavity may actually contribute to an evolving bed shape that can either accelerate or delay retreat under different climate forcing scenarios (e.g Horgan and others, 2013; Li and others, 2022). For example, sedimentation filling space beneath ice shelves has been shown under some bed evolution to help stabilise ice sheets against grounding-line retreat in response to a rise in relative sea level of at least several meters (Alley et al, 2007). Competing influences of enhanced melt leading to thinning of the ice shelves and reduced buttressing possibly work against the potential stabilisation of the grounding zone due to sedimentation processes (Parizek and others, 2013). Where and how the thresholds and sensitivities in the subglacial water flow-sedimentation-melt-enhancement process remain to be understood.

Sedimentation processes themselves are determined by a complex interaction between oceanic flows, including tides and vertical density profiles. As the ocean cavity shallows toward the grounding line, tidal mixing becomes proportionately more important until a tidal front forms, beyond which the water properties are vertically homogenized (Holland, 2008). The extent of this mixed zone is relevant to several questions because a fully mixed region behaves differently to the stratified ocean offshore. Sedimentation rates may be relatively low but at the maximum ner to the grounding zone, on timescales of perhaps decades to centuries.

The approach will be to use a hierarchy of approaches including: the development of theory applied to examine emergent behaviour from the system, and numerical models ranging from idealised pseudo-2d models to more complicated regional applications. Numerical results from the regional modeling  will be useful to compare with  and examine outcomes of field activities planned for future years in the Denman/Shackleton ice shelf region of East Antarctica. The modelling approach will start with using the Ice Shelf version of the Regional Oceanic Modelling System (ROMSIceShelf - e.g. Galton-Fenzi and others, 2012) before transitioning to using a fully coupled ice-sheet/ocean/subglacial model using the Framework for Ice Sheet and Ocean Coupling (FISOC - e.g. Gladstone and others, 2021). ROMSIceShelf is able to simulate sediment laden subglacial water discharge and the interaction with the bed and ice shelf system (see results from the pilot study below).

Relevant questions to answer include:

  • What role does sediment laden subglacial water outflows have on ice shelf melting and bed evolution?
  • What are the dominant oceanic-processes governing sedimentation processes at the grounding zone?
  • How do these processes contribute to melt enhanced feedbacks, ice sheet flow and ice sheet stability under future climate warming?

Primary Supervisor

Meet Ms Chen Zhao

Funding

Applicants will be considered for a Research Training Program (RTP) scholarship or Tasmania Graduate Research Scholarship (TGRS) which, if successful, provides:

  • a living allowance stipend of $28,854 per annum (2022 rate, indexed annually) for 3.5 years
  • a relocation allowance of up to $2,000
  • a tuition fees offset covering the cost of tuition fees for up to four years (domestic applicants only)

If successful, international applicants will receive a University of Tasmania Fees Offset for up to four years.

If successful, applicants will also receive a top-up scholarship of $6,000 per annum for 3.5 years. This scholarship is funded from the Australian Government as part of the Antarctic Science Collaboration Initiative program through the Australian Antarctic Program Partnership (AAPP).

As part of the application process you may indicate if you do not wish to be considered for scholarship funding.

Eligibility

Applicants should review the Higher Degree by Research minimum entry requirements.

Additional eligibility criteria specific to this project/scholarship:

  • Applicants must be able to undertake the project on-campus

Selection Criteria

The project is competitively assessed and awarded.  Selection is based on academic merit and suitability to the project as determined by the College.

Additional essential selection criteria specific to this project:

  • This project will suit candidates with a strong numerical background in quantitative physical sciences

Additional desirable selection criteria specific to this project:

  • Computer programming skills would be advantageous for the running and analysis of simulation results

Application process

There is a three-step application process:

  1. Select your project, and check you meet the eligibility and selection criteria;
  2. Contact the Primary Supervisor, Ms Chen Zhao to discuss your suitability and the project's requirements; and
  3. Submit an application by the closing date listed above.
    • Copy and paste the title of the project from this advertisement into your application. If you don’t correctly do this your application may be rejected.
    • As part of your application, you will be required to submit a covering letter, a CV including 2 x referees and your project research proposal.

Following the application closing date applications will be assessed within the College. Applicants should expect to receive notification of the outcome by email by the advertised outcome date.

Apply now Explore other projects

Why the University of Tasmania?

Worldwide reputation for research excellence

Quality supervision and support

Tasmania offers a unique study lifestyle experience