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 187 Os/ 188 Os 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 187 Os/ 188 Os 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 187 Os/ 188 Os 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.