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 sealevel 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: 1)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. 2) Map and survey (using RTK-GPS) former sea-level features within the same area. 3) Recover and analyse sediments from several potential isolation basins (or shoreline features) to determine the former marine limit and extract a sea-level history.

4) Establish a chronology using cosmogenic-nuclide exposure-age dating, radiocarbon dating and statistical modelling. 5)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. 20-16ka 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.