Holocene relative sea-level changes and deglaciation chronology in Finnmark, northern Norway

Abstract

The outer coast of Finnmark in northern Norway is where the former Fennoscandian and Barents Sea ice sheets coalesced. This key area for isostatic modelling and deglaciation history of the ice sheets has abundant raised shorelines, but only a few existing radiocarbon dates relate to them. Here we present three Holocene sea-level curves based on radiocarbon ages from deposits in isolation basins at the outermost coast of Finnmark; located at the islands Sørøya and Rolvsøya and at the Nordkinn peninsula. We analysed animal and plant remains in the basin deposits to identify the transitions between marine and lacustrine sediments. Terrestrial plant fragments from these transitions were then radiocarbon dated. Radiocarbon-dated mollusk shells and marine macro-algae from the lowermost deposits in several basins suggest that the first land at the outer coast became ice free around 14.6 cal kyr BP. We find that the gradients of the shorelines are much lower than elsewhere along the Norwegian coast because of substantial uplift of the Barents Sea. After the Younger Dryas the coast emerged 1.6-1.0 cm per year until about 9500-9000 cal yr BP. Between 9000 and 7000 yr BP relative sea-level rose 2-4 m and several of the studied lakes became submerged. At the outermost locality Rolvsøya, relative sea level was stable at the transgression highstand for more than 3000 years, between ca. 8000 and 5000 cal yr BP. Deposits in five of the studied lakes were disturbed by the Storegga tsunami ca. 8100-8200 cal yr BP.