A 2500-year record of relative sea-level change at Gress, Isle of Lewis, northwest Scotland using salt marsh sediments

Relative sea-level (RSL) changes in mid-latitude regions commonly reflect complex interactions between global ice-sheet melt, ocean dynamics and glacial isostatic adjustment (GIA), yet high-resolution Late-Holocene records from critical transitional zones near former ice-sheet margins remain sparse. Northwest Scotland, situated near the periphery of the former British-Irish Ice Sheet (BIIS), offers insights into spatially variable RSL trends driven by GIA and regional ice-mass loss, but existing reconstructions are limited in temporal continuity or geographic coverage. Out study addresses this gap by presenting a 2500-year RSL reconstruction from salt marsh sediments at Gress, Isle of Lewis—a location sensitive to BIIS-related lithospheric adjustments. Using a multi proxy approach (lithology, sedimentology, diatom biostratigraphy, and Accelerator Mass Spectrometry 14 C dating), we produced a high resolution RSL record. We found challenges with diatom-based transfer functions due to poor modern analogues in the training set. This led to a qualitative visual assessment of fossil assemblages to reduce paleomarsh surface elevations (PMSEs). Consistent PMSEs show that the marsh surface elevation is a consequence of the rate of sediment accumulation, keeping up with modelled GIA uplift rates. A (1.2 ± 1) m (2σ) RSL rise throughout the core’s 2500-year record was observed, with a slight accelerated sea level rise post-AD 950. RSL rise at ~AD 1300 likely exceeded the background Late-Holocene fall rate (−0.2 mm yr −1 ) until present. It proved challenging to distinguish the effects between barystatic sea level change and local influence on RSL patterns at our site. Any sea level acceleration in the last two millennia remains statistically indistinct in these sediments. Comparison with regional records highlights pronounced spatial heterogeneity in RSL trends, underscoring the influence of local GIA variability.