Holocene palaeoenvironmental reconstruction of sea level, coastal and vegetation changes along the southern Solway Firth, United Kingdom

Holocene relative sea level (RSL) changes were reconstructed from four sites along the less-studied southern Solway Firth. A multiproxy approach, including lithostratigraphical and biostratigraphical analyses, combined with radiocarbon dating, produced ten sea level index points (SLIPs). These SLIPs constrained Holocene RSL changes in the region between ~8300 cal BP and ~6018 cal BP and captured the Main Postglacial Transgression. These ten new points are combined with the ten pre-existing SLIPS from the southern Solway Firth to greatly refine the trend of Holocene RSL changes across this region. The Main Postglacial Transgression was shown to occur between ~8320 and 7500 cal BP, reaching a highstand of 3.26 ± 0.56 mOD. The new data were combined with 73 existing SLIPS from two sites around the northern Solway Firth and compared to RSL predictions from glacial isostatic modelling. Comparison between the corrected SLIPs and RSL predictions using British and Irish ice sheet reconstructions showed that the timing of the Main Postglacial Transgression is best captured with a hybrid model for the presence of thick and thin ice sheets. Pollen analysis at Cowgate Farm and Herd Hill provided a record of vegetation and coastal changes, acting as a chronostratigraphic marker when compared to published pollen records of the region. The records show a general transition from saltmarsh to reed swamp, then peat bog as RSL declined through the mid to late Holocene, with some indications of human clearance in the Bronze Age.