CR2026_22

Title: Simulating Melt Rates in Oceanic Cavities of the Antarctic Ice Sheet

Lead Supervisor: Ryan Patmore, National Oceanography Centre

Co-supervisors: Jim Jordan, Geography, Swansea University; Diego Bruciaferri, Met Office; Harshinie Karunarathna, Civil Engineering, Swansea University; Anthony Wise, National Oceanography Centre

Antarctic Ice Sheet mass loss is one of the largest contributors to uncertainty in projections of future sea level rise. Floating sections of the ice sheet at the continental margines, termed ice shelves, act as an important interface between the ice and ocean. Marine driven melting within ice shelf cavities is the primary source of mass loss along many sections of the Antarctic Ice Sheet (Pritchard et al., 2012, Rignot 2013, 2019). Some of the greatest sources of uncertainty in projecting ice sheet mass loss stem from deficiencies in our representation of this melting. Melt rates depend on two key factors; the temperature of the ocean and how fast it is flowing. Difficulties with observing ice shelf cavities, and the oceanic flow within them, mean that numerical modelling is a crucial source of understanding what cannot be directly observed. This project is aimed at optimising methods for simulating both the marine driven melting and the import of warm water that feeds it. A fresh look will be taken at simulating ocean dynamics within ice shelf cavities, implementing emerging innovations in model coordinate systems and advancing the representation of melt water formation in global climate simulations.

Water depth in ocean models is typically divided into a number of layers, forming a vertical grid. A primary focus of this project is to improve the ocean model grid configuration within ice shelf cavities, with a particular interest in accurate representation of the physics and ocean velocity at the sloping ice shelf-ocean interface. It has long been identified that existing grid representations, which align with either the seabed topography (sigma-coordinate) or gravity (z-coordinate), have limitations when it comes to realistically representing the physics at sloping boundaries (Gwyther et al., 2020). sigma-coordinates generate biases near steep transitions in water column thickness and z-coordinates have a stepped representation of topography that may generate spurious mixing. Recent developments have seen the introduction of new gridding approaches that merge the sigma and z representations and can dramatically improve results (e.g., Bruciaferri et al., 2018, 2020, 2022, Wise et al., 2023, Bruciaferri et al., 2024). These new approaches have yet to be implemented within ice shelf cavities, offering a unique opportunity to improve the representation of marine driven ice shelf melt by more accurately simulating ocean velocities and temperatures. This project will investigate the benefits of these new coordinates within ice shelf cavities and identify the impact of implementation choices.

This exciting science programme will feed directly into the NOC global ocean modelling agenda, which is developing state-of-the-art modelling systems and contributing to leading international climate projections. The investigation will begin on a single ice shelf basis, starting with idealised experiments using the NEMO ocean model. The initial exploration will be followed by an opportunity to apply the new methods to more realistic settings such as the Bellingshausen or Amundsen seas of West Antarctica. There will also be scope to combine these methods in a coupled ice sheet-ocean system using the Úa model with which the second supervisor (Jordan) at Swansea University is intimately familiar. Configuring models of this complexity is a highly specialised role that requires significant investment of time and expertise. Following the track-record of the NOC and the Met Office in reproducible modelling (Polton et al., 2023) under the Joint Marine Modelling Programme (JMMP), the candidate will have the opportunity to cement their standing in the field via the generation of open-source software tools for configuring model domains with the new approaches developed under this programme.

Illustration of (a) z, and (b) sigma coordinate representations in an ocean model adapted from Bruciaferri et al. (2018). (c) Schematic representation of ice shelf cavity.

Training opportunities:

The candidate will have opportunities to develop skills and expertise in Oceanic and Cryospheric sciences and modelling, via:Participation in sea-going expeditions to the Southern Ocean or elsewhere on a British Antarctic Survey or NOC shipA three-month placement at the UK Met OfficeAttendance of the Fluid Dynamics, Oceanography and Glaciology summer schoolsEmersion in Swansea University’s Climate Action Research Institute and Centre of Expertise in Ice and Climate

Student profile:

This project would be suitable for students with a first degree in mathematics, physics, or a closely related environmental or physical science. Basic programming skills in languages such as Python, Matlab or R are desirable, but not essential for consideration. UKRI funding only covers Home fees which increase annually. For this project, the difference in the Home fees and international fees will be covered and international students will not be required to meet the difference themselves.

References:

Bruciaferri, D., Shapiro, G. I., & Wobus, F. (2018). A multi-envelope vertical coordinate system for numerical ocean modelling. Ocean Dynamics, 68, 1239–1258. https://doi.org/10.1007/s10236-018-1189-x
Bruciaferri, D., Shapiro, G. I., Stanichny, S., Zatsepin, A., Ezer, T., Wobus, F., Francis, X., & Hilton, D. (2020). The development of a 3D computational mesh to improve the representation of dynamic processes: The Black Sea test case. Ocean Modelling, 146, 101534. https://doi.org/10.1016/j.ocemod.2019.101534
Bruciaferri, D., Tonani, M., Ascione, I., Al Senafi, F., O’Dea, E., Hewitt, H. T., & Saulter, A. (2022). GULF18, a high-resolution NEMO-based tidal ocean model of the Arabian/Persian Gulf. Geoscientific Model Development, 15, 8705–8730. https://doi.org/10.5194/gmd-15-8705-2022
Bruciaferri, D., Guiavarc’h, C., Hewitt, H. T., Harle, J., Almansi, M., Mathiot, P., & Colombo, P. (2024). Localized general vertical coordinates for quasi-Eulerian ocean models: The Nordic overflows test-case. Journal of Advances in Modeling Earth Systems, 16, e2023MS003893. https://doi.org/10.1029/2023MS003893
Gwyther, D. E., Kusahara, K., Asay-Davis, X. S., Dinniman, M. S., & Galton-Fenzi, B. K. (2020). Vertical processes and resolution impact ice shelf basal melting: A multi-model study. Ocean Modelling, 147, 101569. https://doi.org/10.1016/j.ocemod.2020.101569
Polton, J., Harle, J., Holt, J., Katavouta, A., Partridge, D., Jardine, J., Wakelin, S., Rulent, J., Wise, A., Hutchinson, K., Byrne, D., Bruciaferri, D., O’Dea, E., De Dominicis, M., Mathiot, P., Coward, A., Yool, A., Palmiéri, J., Lessin, G., Mayorga-Adame, C. G., Le Guennec, V., Arnold, A., & Rousset, C. (2023). Reproducible and relocatable regional ocean modelling: Fundamentals and practices. Geoscientific Model Development, 16, 1481–1510. https://doi.org/10.5194/gmd-16-1481-2023
Pritchard, H., Ligtenberg, S., Fricker, H., et al. (2012). Antarctic ice-sheet loss driven by basal melting of ice shelves. Nature, 484, 502–505. https://doi.org/10.1038/nature10968
Rignot, E., et al. (2013). Ice-shelf melting around Antarctica. Science, 341, 266–270. https://doi.org/10.1126/science.1235798
Rignot, E., Mouginot, K., Scheuchl, B., van den Broeke, M., van Wessem, M. J., & Morlighem, M. (2019). Four decades of Antarctic Ice Sheet mass balance from 1979–2017. Proceedings of the National Academy of Sciences of the United States of America, 116(4), 1095–1103. https://doi.org/10.1073/pnas.1812883116
Wise, A., Harle, J., Bruciaferri, D., O’Dea, E., & Polton, J. (2022). The effect of vertical coordinates on the accuracy of a shelf sea model. Ocean Modelling, 170, 101935. https://doi.org/10.1016/j.ocemod.2021.101935

CR2026_22

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