IAP2-23-109

Rapid deglaciation and sea-level change on the Outer Hebrides, Scotland

Reconstructing the behaviour of former ice sheets and trajectory of sea-level change is vitally important for constraining numerical models and refining predictions of future sea-level rise (IPCC, 2022). Sophisticated glacial-isostatic adjustment (GIA) models, used to predict long-term land and sea-level changes, generally show good agreement with empirically derived postglacial sea-level curves from around the British Isles (Bradley et al., 2011; Shennan et al., 2018; Bradley et al., 2023). But these models struggle to predict relative sea-level (RSL) variations at sites around the NW margins of the last British-Irish ice sheet complex. This uncertainty partly stems from a lack of good empirical data constraints across much of the Outer Hebrides, but probably also results from the particular ice-sheet dynamics that operated in this sector. The Minch ice stream dominated the flow configuration of the NW sector of the last British-Irish Ice Sheet. Its rapid collapse (Bradwell et al., 2019, 2021) almost certainly influenced RSL changes in NW Scotland on either side of this wide sea strait (Simms et al., 2022). A multi-institute NSF-NERC funded project is currently seeking to explore this relationship on the NW Scottish Mainland, from Skye to Assynt. This PhD doctoral training project, supervised by members of the same research team, will seek to address some of these questions in the Outer Hebrides – an important but long-standing data gap.

This PhD project will focus on reconstructing the deglaciation and sea-level history of the eastern seaboard of the Outer Hebrides – concentrating on the central area adjacent to the Minch, from SE Lewis to Benbecula. This large and little-studied area includes a wide range of unmapped glacio-geomorphological evidence relating to the latter stages of ice sheet / ice cap retreat as well as numerous potential isolation basins preserving a signal of relative sea-level change since deglaciation. Importantly, by combining geomorphological mapping, geochronology, sedimentology, micro-fossil analysis and high-resolution survey techniques this project will address a number of research questions simultaneously, whilst also offering training in a wide suite of research techniques rarely applied in a single project.

The key aims of this PhD research project will be to:
• Map and characterise the different sediment-landform assemblages relating to former ice flow and deglaciation of the Outer Hebrides ice sheet / ice cap, from SE Lewis to Benbecula.
• Map and survey (using RTK-GPS) former sea-level features within the same area.
• Recover and analyse sediments from several potential isolation basins (or shoreline features) to determine the former marine limit and extract a sea-level history.
• Establish a chronology using cosmogenic-nuclide exposure-age dating, radiocarbon dating and statistical modelling.
• Explore the connections between the reconstructed ice-sheet and sea-level history of the eastern Outer Hebrides and the rapid deglaciation of the Minch ice stream (ca. 20-16 ka BP).

The successful student will be encouraged to present at conferences and publish journal articles at well-defined stages of their research. The outcomes of this research will feed into numerical ice-sheet models and international databases and also form part of a wider (funded) research project to understand the sea-level and ice-sheet history of NW Scotland.

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Image Captions

Fieldwork in the Outer Hebrides [photo: T. Bradwell]

Methodology

This PhD project will involve at least 2 field seasons in the Outer Hebrides – a landscape like nowhere else in Europe. The research methodology will be multi-disciplinary, supervised by recognised experts at 3 institutions working in palaeo-glaciology, sea-level research, geomorphology, geochronology and palaeo-environmental reconstruction. This studentship will involve mapping from new remote-sensing datasets and surveying in the field; basin coring; sedimentological analysis; rock sampling and sample preparation for cosmogenic nuclide analysis; micro-fossil analysis; sampling for radiocarbon analysis; and statistical model development – all within a 3.5 year programme of study.

The studentship will be based in Stirling, with support from Durham University and University of Glasgow / Scottish Universities Environmental Research Centre (SUERC). The student will also have access to the world-class laboratory facilities at SUERC, East Kilbride, as well as other state-of-the-art facilities if/when appropriate. The successful candidate will work with a team of international researchers and collaborators investigating former ice-sheet and sea-level change in NW Scotland and elsewhere (University of California, Santa Barbara; University of Michigan; Durham; Stirling; Sheffield, Gloucestershire Glasgow/SUERC).

Project Timeline

Year 1

• Systematic review of previous work and methodological capabilities (Autumn 2024)
• Research design and DTP training methods
• Outer Hebrides fieldwork (June 2025): landform mapping & GPS surveying; terrestrial cosmogenic nuclide (TCN) sampling and basin coring (Loch Sealg, SE Lewis; Scalpay; and around Flodabay, South Harris)
• PhD progression paper & Symposium (Yr1)
• UK Conference presentation (Sept 2025)

Year 2

• Advanced skills training; proposal writing
• Core analysis; non-destructive testing
• TCN preparation and analyses (SUERC)
• Outer Hebrides fieldwork (May 2026): landform mapping & GPS surveying; terrestrial cosmogenic nuclide (TCN) sampling and basin coring (Sound of Harris; Loch Maddy, North Uist; Grimsay, North Uist / Benbecula)
• Lab-based sediment & micro-fossil analysis
• Manuscript preparation & submission
• Yr2 annual review (Sept 2026)

Year 3

• Final fieldwork data collection (May 2027)
• Continued sedimentological analyses
• Chronological / statistical modelling
• Data assimilation and thesis ‘workshop’
• Manuscript preparation & submission

Year 3.5

• Focused thesis write-up
• International conference presentation
• Finalise & submit thesis for PhD examination

Training
& Skills

Training in specialist and complementary transferable skills is the most important aspect of a PhD programme. This PhD comes with a generous £10k Research and Training Support Grant to cover internal and external training, analytical costs and consumables. It will also provide all funds for fieldwork, and reasonable UK travel costs to/from academic institutions, and funding to attend at least 1 overseas conference and 1 UK-based conference.

Specialist training will be provided in: GIS, geomorphological mapping; RTK-GPS surveying and data analysis; sediment analysis techniques; TCN sampling; micro-fossil sample preparation and analysis; construction of chronological models, using Bayesian methods; statistical techniques using R; and bespoke training for high-quality oral presentation, manuscript and poster production. The successful candidate will be expected to contribute to the evolution and enhancement of the methodology throughout the lifetime of the project.

As a NERC-IAPETUS2 student, in Year 1, she/he will also receive more generic doctoral training in research skills and techniques; health and safety in the workplace; effective research environment; research management; personal effectiveness; communication skills; manuscript and grant writing; networking and team-working; thesis troubleshooting; interview preparation and career management. The student will join a vibrant community of staff and postgraduate students at the University of Stirling (BES) and will also be part of the wider NERC / IAPETUS postgraduate group.

References & further reading

Bradley, S.L., Milne, G.A., Shennan, I., Edwards, R. 2011. An improved glacial isostatic adjustment model for the British Isles. Journal of Quaternary Science, 26, 541–552.

Bradley, S.L., Ely, J.C., Clark, C.D., Edwards, R.J., Shennan, I. 2023. Reconstruction of the palaeo-sea level of Britain and Ireland arising from empirical constraints of ice extent: implications for regional sea level forecasts and North American ice sheet volume. Journal of Quaternary Science, 38: 791-805.

Bradwell, T., Small, D., Fabel, D., Smedley, R.K., Clark, C.D. et al. 2019. Ice-stream demise dynamically conditioned by trough shape and bed strength. Science Advances, 5: eaau1380. DOI: 10.1126/sciadv.aau1380

Bradwell, T., Fabel, D., Clark, C.D., Chiverrell, R.C., Small, D. et al. 2021. Pattern, style and timing of British–Irish Ice Sheet advance and retreat over the last 45 000 years: evidence from NW Scotland and the adjacent continental shelf. Journal of Quaternary Science, 36, 871–933.

IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Masson-Delmotte, V., et al. (Eds.) Cambridge University Press, 2391 pp.

Shennan, I., Bradley, S.L., Edwards, R. 2018. Relative sea-level changes and crustal movements in Britain and Ireland since the Last Glacial Maximum. Quaternary Science Reviews, 188, 143–159.

Simms, A.R., Best, L., Shennan, I., Bradley, S., Small, D., et al. 2022. Investigating the roles of relative sea-level change and glacio-isostatic adjustment on the retreat of a marine-based ice stream in NW Scotland. Quaternary Science Reviews, 277: 107366

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