Quantifying variable rates of postglacial relative sea level fall from a cluster of 24 isolation basins in southern Norway

Sediment sequences obtained from 24 isolation basins located on the Skagerrak coastline are used to develop new sea level index points for southern Norway. The basins are located near a common shoreline isobase and extend from marine limit at c. 83 m asl. to present sea level. The abundance of bedrock isolation basins within the small study area enables a high-resolution reconstruction of postglacial relative sea-level change. For most of the basin records, 3-5 samples of terrestrial plant macrofossils were radiocarbon dated across the biostratigraphically-defined isolation boundary. Eight of the isolation events were further constrained by Bayesian modelling of the radiocarbon age results. The overall reconstructed sea-level history is as expected for a formerly glaciated coastline; consisting of a rapid regression from marine limit followed by a slower pace of relative sea level fall from early-mid Holocene to present. The new dataset of sea level index points, however, further delineates century-scale oscillations in rates of sea level regression, which record past changes in sea surface height and vertical land motion (glacial isostatic adjustments, GIA). Results provide new constraints for future numerical models aimed at reducing uncertainty in century-scale relative sea-level projections for Fennoscandia.