Evidence of early deglaciation (18 000 cal a bp ) and a postglacial relative sea‐level curve from southern Karmøy, south‐west Norway

Based on six consistent radiocarbon dates from the isolation basins Grodheimsvatnet and Kringlemyr, we estimate a minimum deglaciation age for southern Karmoy, an island in outer Boknafjorden (south-west Norway), of around 18 000 calibrated years before present (18k cal a bp). We use microscopic phytoplankton, macrofossils, lithostratigraphic evidence and X-ray fluorescence data to identify the isolation contacts in the basins, and date them to 17.52-17.18k cal a bp in Grodheimsvatnet [15.57 m above present mean sea level (MSL)] and 16.19-15.80k cal a bp in Kringlemyr (11.99 m above MSL). Combining these data with previous studies, we construct a relative sea-level (RSL) curve from 18k cal a bp until the present, which is similar to 3 ka longer than any previous RSL reconstruction from southern Norway. Following deglaciation, southern Karmoy has experienced a net emergence of around 16-19 m, although with significant RSL fluctuations. This includes two RSL minima well below present MSL around similar to 13.8 and similar to 10k cal a bp, and two maxima that culminated around 5-7 m above MSL during the Younger Dryas and early to mid-Holocene, respectively. Considering eustatic sea level and modelled gravitational deformation of the geoid, we estimate a net postglacial isostatic uplift of similar to 120 m.