IAP2-22-440

Tracking past sea-level change In Western Scotland with a novel multi-proxy approach

Records of sea-level change from locations proximal to former Northern Hemisphere ice sheets are crucial for improving our understanding of past ice sheet extent, constraining models of solid Earth feedbacks that control sea-level rise and establishing the sources of meltwater pulses to the ocean. Models suggest the interaction between sea-level change and ice margin stability is crucial in controlling rates and style of ice sheet retreat with knock-on implications for future sea-level rise. Reconstructing sea level on various temporal scales and understanding how it interacted with ice stream/ice sheet retreat provides a way to test models used to predict future change.

Northwest Scotland has produced the longest record of past sea-level change in the UK (Shennan et al., 2005). However, there are significant mis-matches between data and the computer models that are required to make accurate predictions of future sea-level change (Shennan et al., 2018). Improving these models requires additional long-term records of sea-level change and details of the interaction between sea-level change and ice sheets during periods of restricted ice extent and deglaciation. Additionally, there are several enigmatic sites that are potentially much older and offer potential to extend the record of past sea-level change to previous interglacial periods.

This project aims to use a novel, multi-proxy approach to produce new records of sea-level change from northwest Scotland. In several places (e.g. Islay, Jura and the Wester Ross coastline) raised cobble beaches mark sea levels higher than present, including some that are higher than reconstructed sea-levels for the end of the last glaciation (e.g. Dawson et al., 1998; Sissons and Dawson, 1981). Accurately mapping and dating these highest raised beaches is of critical importance in improving our understanding of the interaction between sea-level change and ice sheet/ice stream stability. In the past it has been very difficult to accurately date these raised cobble beaches. However, recent developments in the application of cosmogenic nuclide techniques have successfully produced a chronology for some of the raised shorelines on Jura (Dawson et al., 2022). This project will use a combination of approaches, combining the use of optically stimulated luminescence (OSL) and cosmogenic nuclide dating to provide new constraints on former sea levels at new temporal scales and resolutions. In addition, basal radiocarbon dates from sediments preserved in lochans impounded by raised gravel beaches can provide minimum ages for beach development. Sea-level reconstructions will also be based on sediments preserved in isolation basins (e.g. Long et al., 2011), natural rock-lipped depressions that can either be connected to, or isolated from the sea depending on changes in sea level.

Sites will be chosen from a range of altitudes from close to and above the highest altitude of sea level following the Last Glacial Maximum, down to, and below, present day sea level to constrain sea-level change through the Lateglacial and Holocene. Combining multiple, independent constraints on past sea-level change on long time scales provides a robust record that is ideal for testing and helping to constrain models of glacio-isostatic adjustment.

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Image Captions

Raised shorelines from the Applecross Peninsula, NW Scotland (photo: J.M. Lloyd)

Methodology

To achieve these aims the student will identify and map suitable field sites prior to undertaking fieldwork to collect samples for dating from raised beaches and collect sediment cores from impounded lochans and isolation basins. This project will benefit from close collaboration with an ongoing joint US-UK funded project (Beach to Basins GIA) led by Prof. Alex Simms (UCSB) working on past sea-level change since the LGM in the Minch area of northwest Scotland. This will include participation in field campaigns as part of the Beach to Basins GIA project as well as independent fieldwork to other sites on Islay and Jura.

A range of proxies will be used to identify formation of impounded lochans and marine isolation and inundation from isolation basin sediment cores. These will include microfossils and a range of sedimentological and geochemical analyses (foraminiferal and/or diatom analysis, total organic carbon (TOC), XRF scanning, x-rays and multi-sensor core logging). The chronology for the sediment cores will be developed using radiocarbon dating of organic rich sediments. Analyses will be undertaken using the extensive facilities available at Durham University, University of Gloucestershire (external supervisor, Dr Louise Best) and via the NERC Environmental Isotope Facility. We will use relatively recent developments in OSL and cosmogenic nuclide dating techniques to constrain the age of the raised beaches. Luminescence dating will be undertaken at the Liverpool Luminescence Laboratory in collaboration with external project partner Smedley. Cosmogenic nuclide dating will be carried out using an application to the NERC facility – NEIF Cosmo.

The new data will be synthesised to produce new well-constrained records of sea-level change that can be used to test new and existing model output and help refine future model developments.

Project Timeline

Year 1

Review existing literature on relative sea-level and ice sheet history in west Scotland. Map potential field sites. Plan and undertake field season by end of Year 1. Engage in Faculty training programme and complete first year Progression Paper to detail project overview, research questions, and planned methodology.

Year 2

Undertake main laboratory component with potentially additional fieldwork. Sub-sampling cores, collect multi-proxy data (e.g. foraminiferal fauna, TOC, XRF scanning, x-rays and MSCL). Extended visit to Liverpool to date raised beach samples using OSL. Submit radiocarbon samples through NERC Radiocarbon facility and apply for cosmogenic nuclide support through NEIF-Cosmo. Preparation of preliminary review chapters. Present initial results at national postgraduate conference.

Year 3

Finalise laboratory work. Data analysis and interpretation, synthesise multiple proxy records to interpret sea-level change. Construct relative sea-level curves. Begin write up of major results, including presentation at international conference (e.g. EGU). Begin thesis write up.

Year 3.5

Preparation and completion of final chapters for thesis. Submission of papers for publication.

Training
& Skills

The student will receive training in geomorphological field mapping, specifically the identification of raised shorelines (Stirling) and also in collection of core material from isolation basin environments and in sediment core description (Durham and Newcastle). Training in proxy techniques (microfossil, sedimentological and geochemical teachniques) will be provided in state-of-the-art laboratories in the Department of Geography, Durham. The student will be trained in sample collection, preparation and analysis for luminescence dating at the world-leading Liverpool Luminescence Laboratory and also cosmogenic nuclide dating (Durham). The student will be a member of the Sea Level, Ice Sheets and Climate research cluster in Durham Geography (https://www.dur.ac.uk/geography/icesheetsandsealevel/). The student will further be supported to attend appropriate summer school opportunities (e.g. SUERC Geochronology summer school)

Broader transferable skills (e.g. communicating science, thesis writing, writing for publication, presentation skills) will be developed through various training events at Durham University offered by IAPETUS as well as through Durham’s award-winning Career and Research Development (CAROD) group. At all stages the students writing skills will be developed and supported and they will be encouraged to submit supplementary funding applications and lead papers outlining the projects results. The project and supervisory team is designed to give the student broad, multi-disciplinary training including quantitative skills to ensure they have a range of applicable and transferable skills.

References & further reading

Callard, S.L., et al., 2018. Extent and retreat history of the Barra Fan Ice Stream offshore western Scotland and northern Ireland during the last glaciation. Quaternary Science Reviews, 201, 280-302.
Dawson, A.G., 1982. Lateglacial sea-level changes and ice-limits in Islay, Jura and Scarba, Scottish Inner Hebrides. Scottish Journal of Geology, 18, 253-265.
Dawson, A.G., et al., 1998. Lateglacial climate change and coastal evolution in western Jura, Scottish Inner Hebrides. Geologie en Mijnbouw, 77, 225-232.
Dawson, A.G., Bishop, P., Hansom, J., Fabel, D. 2022. 10Be exposure age dating of Late Quaternary relative sea-level changes and deglaciation of W Jura and NE Islay, Scottish Inner Hebrides. Earth and Environmental Science Transactions of the Royal Society of Edinburgh https://doi.org/10.1017/S175569102200010X
Long, A.J., et al., 2011. Isolation basins, sea-level changes and the Holocene history of the Greenland Ice Sheet. Quaternary Science Reviews 30, 3748-3768.
Oppenheimer, M. et al., 2019. Sea level rise and implications for low lying islands, coasts and communities. IPCC Special Report on the Ocean and Cryosphere in a Changing Climate.
Shennan, I., et al., 2005. A 16 000-year record of near-field relative sea-level changes, northwest Scotland, United Kingdom. Quaternary International, 133, 95-106.
Shennan, I., et al., 2018. Relative sea-level changes and crustal movements in Britain and Ireland since the Last Glacial Maximum. Quaternary Science Reviews, 188, 143-159.
Siegert, M., et al., 2020. Twenty-first century sea-level rise could exceed IPCC projections for strong-warming futures. One Earth, 3, 691-703.
Sissons, J.B. and Dawson, A.G. 1981. Former sea-levels and ice limits in part of Wester Ross, northwest Scotland. Proceedings of the Geological Association 92 (2), 115-124.

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