From Ice to Isolation: A geochemical reconstruction of the palaeoenvironmental evolution of Gairloch, NW Scotland (UK), since the Last Glacial Maximum

Abstract

Complex relative sea-level (RSL) changes are associated with the deglaciation of the British and Irish Ice Sheet (BIIS). Sediment archives from Loch Bad na h-Achlaise, an isolation basin in NW Scotland, UK, span Late Glacial to Holocene time and record sea-level change and ice proximity via a geochemical and biostratigraphic multiproxy approach. Osmium and carbon isotope, carbon and nitrogen content, and X-ray fluorescence (XRF) data suggest that the basal sedimentary unit reflects a glaciomarine depositional setting, a finding previously unresolved due to an inadequate biostratigraphic framework. The ¹⁸⁷Os/¹⁸⁸Os record from the basin captures the RSL history of this site and illustrates the interplay between the local signal of glacial isostatic adjustment and the non-local signal of glacio-eustatic sea-level rise. By coupling the ¹⁸⁷Os/¹⁸⁸Os data with a detailed age–depth model, our study demonstrates a period of RSL fall between 16.2 and 15.9 cal ka BP, which culminates in basin isolation. The close agreement between the biostratigraphy, where available, and the ¹⁸⁷Os/¹⁸⁸Os record confirms the viability of this isotope system as an RSL proxy not reliant on microfossil preservation and thus a potentially effective approach when poor microfossil preservation hampers palaeoenvironmental reconstruction.