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Projects

CHannelized Ice Shelf Melting (CHISM)

(a) Example digital elevation product from one 2-year period (2013–2015) of Pine Island Glacier (PIG), West Antarctica: 256 m WorldView mosaic; (b) Mean 2008–2015 basal melt-rate composite8; (c) Looking upward and sideways, along-track observation of the basal depth (colour) imaged by Autosub crossing two longitudinal channels of PIG. Along-track and across-track scales are not equal; see white scale bars indicating 20 m in the vertical scale and 200 m in the horizontal scale; (d) Fractured and caved ice walls surrounding the ice cove at the terminus of the southern shear margin of the PIG. Photograph by Maria Stenzel; (e) Autosub 3 being deployed in front of PIG. Photograph by Pierre Dutrieux

 

Background

Ice shelves buttress1 continent-size ice sheets. Their present and future stability will largely dictate global sea level variations in the next decades to century2 . Oceanic melting of ice shelves is often concentrated in channels at the ice ice shelf base3–5, where a buoyant meltwater plume entrains relatively warm ambient water, driving melt and further carving the channelised geometry6,7. Such features can be readily observed at the surface of the ice, as bottom relief is reflected by the floating medium, and are somewhat ubiquitous. Yet, such kilometre-scale ice/ocean coupled dynamic has only been observed quantitatively in a couple of specific datasets, involving satellite, airborne and in situ observations. To date, a variety of methods and techniques led to somewhat conflicting conclusions about the importance of channelised melt. They could minimize melt integrated over individual ice shelves (a stabilizing effect), or inversely create structural weaknesses eventually leading to ice shelf calving and disintegration (a destabilizing effect). The advent of high resolution satellite capabilities over the past decade allows for a generalization of regional methods to continental scales, to finally obtain a much more statistically significant understanding of these systems, their relationships with larger scale variables characterizing ice (velocity, geometry) and ocean (circulation, temperature) dynamics, and their impact on sea level projections.

Aims, Objectives and Methodology

In this project, the student will work with leading scientists towards a comprehensive spatial and temporal coverage of channelized melt allowing comparison between Antarctic ice shelf settings. Laser and radar altimetry data from ICESat-2 and CryoSat-2 will be processed at high spatial resolution in order to measure the presence and evolution of sub-shelf melt channels. This will provide a decade long record of basal melt which combined with unique oceanography measurements will improve our understanding of ice[1]ocean interactions. Satellite-based results will be compared with various in situ observations to discern reasonable from more approximate assumptions about the physical world. A variety of simple (1-D, 2-D plume) and more complex (3-D state-of-the-art) ocean models will be implemented to represent channelized ocean melt and identify flaws in current parametrizations used in Earth System models. Finally, a detailed, continent-wide analysis of the relationship between channel geometry, associated melt, and rift/calving processes of ice shelves will be carried out. Advanced computer techniques (e.g. Machine Learning) will be used to identify and track channelized melt, its evolution and eventual relationships with ice fractures and calving processes, and to improve our understanding of the co-evolution of channels with spatially sparse and non-repeat samples of ocean properties.

Training

Through participating in this project, the student will gain advanced skills in earth observation and in cutting-edge computational and numerical techniques. You will become a valued member of the world-class Cryosphere research group at the British Antarctic Survey. The supervisory team are world experts in their respective specialties, ensuring that the student will be well integrated into the international science community. You will be encouraged to attend and present your work at national and international conferences, and will be supported to publish your findings in leading academic journals. The student will have further opportunities for multi-disciplinary training through, for example, summer schools in Karthaus in the Italian Alps and through participating in supervisors’ Antarctic fieldwork.

Requirements
This project is well-suited to an enthusiastic candidate with an interest in working in rigorous, international, fast-moving climate research that can have a real impact on high-level policy (for example through the IPCC assessment reports). The ideal candidate will have a strong quantitative and analytical background as could be demonstrated by, for example, an undergraduate and/or masters degree in physics, engineering, earth sciences, physical geography, mathematics or computer science. The student will run sophisticated numerical models and analyse complex datasets, so that prior experience of scientific computing and writing code may be an advantage. An ability to communicate complex ideas in a simple fashion will also be valuable. A specific background in glaciology or climate sciences is not required.

The student will be based at the British Antarctic Survey in Cambridge and registered at the University of Leeds. Applicants are encouraged to contact the primary supervisor to discuss the project.

Further Reading
1. Gudmundsson, G. H. Ice-shelf buttressing and the stability of marine ice sheets. Cryosphere 7, 647–655 (2013). 2. Joughin, I., Shapero, D., Smith, B., Dutrieux, P. & Barham, M. Ice-shelf retreat drives recent Pine Island Glacier speedup. Science Advances 7, eabg3080 (2021). 3. Dutrieux, P. et al. Basal terraces on melting ice shelves. Geophysical Research Letters 41, 5506–5513 (2014). 4. Dutrieux, P. et al. Pine Island glacier ice shelf melt distributed at kilometre scales. The Cryosphere 7, 1543–1555 (2013). 5. Gourmelen, N. et al. Channelized Melting Drives Thinning Under a Rapidly Melting Antarctic Ice Shelf. Geophysical Research Letters 44, 9796–9804 (2017). 6. Millgate, T., Holland, P. R., Jenkins, A. & Johnson, H. L. The effect of basal channels on oceanic ice-shelf melting. Journal of Geophysical Research: Oceans 118, 6951–6964 (2013). 7. Gladish, C. V., Holland, D. M., Holland, P. R. & Price, S. F. Ice-shelf basal channels in a coupled ice/ocean model. Journal of Glaciology 58, 1227–1244 (2012). 8. Shean, D. E., Joughin, I. R., Dutrieux, P., Smith, B. E. & Berthier, E. Ice shelf basal melt rates from a high-resolution digital elevation model (DEM) record for Pine Island Glacier, Antarctica. The Cryosphere 13, 2633–2656 (2019).