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

Overview

By the end of this century global sea levels are predicted to be rising by up to 15 mm/yr, with a total sea-level rise of 1 m under worst-case scenarios (Oppenheimer et al., 2019). There is, however, large uncertainty with these estimates partly associated with uncertainty surrounding future mass loss from the Antarctic and Greenland Ice Sheets (potentially contributing an additional 2 m within the next 100 years, Siegert et al., 2020). Models suggest the interaction between sea-level change and ice margin stability is potentially crucial in controlling rates and style of ice sheet retreat with knock-on implications for sea-level rise. This uncertainty hinders efforts to mitigate future sea-level rise. Reconstructing past sea levels and their interaction with ice stream/ice-sheet retreat provides a way to test models of future change.

Western Scotland has produced the longest record of past sea-level change in the UK (Shennan et al., 2005). However, there are still 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, including details of the interaction between sea-level change and ice-margin instability during the period of early deglaciation. The islands of Islay and Jura, off the west coast of Scotland, are ideal candidates to produce such records. There have been relatively few studies investigating sea-level changes from these islands, however, they host a range of landforms that document former, higher-than-present sea-levels (e.g. A.G Dawson; 1982, A.G Dawson et al., 1998; S Dawson et al., 1998) yet the precise timing of the changes in sea level remains poorly constrained. These Inner Hebridean islands are also well positioned to track deglaciation across the continental shelf and the potential link with sea-level change.

This project aims to use a novel, multi-proxy approach to produce new records of sea-level change from western Scotland. Both Islay and Jura (in particular) have a large number of raised gravel beaches marking sea levels higher than present. Many of these raised beaches impound small lochans. Sea-level reconstructions will be derived from the raised beaches by directly dating the deposits using luminescence dating and radiocarbon dating of juvenile molluscs (Long et al., 2012). The age of the raised beaches will also be constrained by dating sediments preserved in the impounded lochans – basal radiocarbon dates will provide a minimum age for barrier development. In addition sea-level reconstructions will also be based on sediments preserved in isolation basins (e.g. Long et al., 2011; Brader et al., 2017), 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 the marine limit (highest altitude) to constrain the timing of initial deglaciation, 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 provides a robust record that is ideal for testing and helping to constrain models of glacio-isostatic adjustment.

Methodology

To achieve these aims the student will map and identify suitable field sites prior to undertaking fieldwork to collect sediment cores from impounded lochans and isolation basins and samples for luminescence and radiocarbon dating from raised beaches. Isolation basins will be surveyed using Ground Penetrating radar. Cores will be collected using a gouge corer and Russian sampler typically from an inflatable dingy, though where basins have been infilled this will not be necessary.

A range of proxies will be used to reconstruct sea-level change from isolation basin sediment cores. These will include microfossil, sedimentological and geochemical analyses (foraminiferal and/or diatom analysis, total organic carbon (TOC), XRF scanning, x-rays and multi-sensor core logging, bulk carbon isotopes). 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 and via the NERC Environmental Isotope Facility. Luminescence dating will be undertaken at the Liverpool Luminescence Laboratory in collaboration with external project partner Smedley.

The new data will be synthesised to produce a new well-constrained record of sea-level change that can be used to test 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 W Scotland. Map potential field sites. Undertake training in main lab techniques. 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 and 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. 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 collection of core material from inland waters and 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. The student will be a member of 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

Brader, M.D., Lloyd, J.M., Barlow, N.L., Norðdahl, H., Bentley, M.J., Newton, A.J. 2017. Postglacial relative sea-level changes in northwest Iceland: evidence from isolation basins and coastal lowland sediments. Quaternary Science Reviews 169, 114 – 130.

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, S., Dawson, A.G. and Edwards, K.J., 1998. Rapid Holocene relative sea-level changes in Gruinart, Isle of Islay, Scottish Inner Hebrides. The Holocene, 8, 183-195.

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.

Long, A.J., Strzelecki, M.C., Lloyd, J.M., Bryant, C. 2012. Dating High Arctic Holocene relative sea level changes using juvenile articulated marine shells in raised beaches. Quaternary Science Reviews 48, 61-66.

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.

Further Information

For furtehr information please contact any of the following:
Dr Jerry Lloyd, j.m.lloyd@durham.ac.uk
Dr Louse Callard, louise.callard@newcastle.ac.uk
Dr David Small, david.p.small@durham.ac.uk
Dr Rachel Smedley, Rachel.Smedley@liverpool.ac.uk

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