Late Weichselian and early Holocene changes of vegetation, climate and sea level on the Skagi peninsula, northern Iceland

Abstract: Sediment sequences from five lakes on the Skagi peninsula, northern Iceland, were subjected to mineral magnetic analysis, carbon analysis, pollen analysis, plant macrofossil analysis, diatom analysis, radiocarbon dating and tephra analysis in order to make detailed reconstructions of vegetation, climate and sea level during the Late Weichselian and Early Holocene. The main purpose was to investigate if the dramatic deglacial climatic shifts recorded in proxy records from the North Atlantic region, such as ice cores, marine sediments and lake sediments, also are registered in Skagi lake sediments, which would be expected considering Iceland´s position in the middle of the North Atlantic Ocean, within the range of the Late Weichselian–Early Holocene migrations of the marine polar front. In addition, the project aimed at a better understanding of the environmental development on Iceland during the last deglaciation. The period 11,300-10,900 BP was found to be characterized by grass-tundra vegetation and low lake productivity, indicating cold climatic conditions. In addition, there was an overall fall in relative sea level. Milder conditions after 10,900 BP are reflected by an expansion of dwarf shrubs and increased limnic productivity, indicating long seasons without sea ice. Relative sea level continued to fall in the period 10,900-10,600 BP. An abrupt cooling at 10,600 BP caused a return to grass-tundra vegetation and low limnic productivity, and sea-ice conditions were probably heavy up to 9900 BP. A minor transgression occurred in the later part of this cold period. Abrupt warming at 9900 BP resulted in a change to herb-tundra vegetation and high lake productivity, indicating long seasons without sea ice. Relative sea level fell rapidly after 9900 BP, but turned into a minor transgression in the period 9800-9700 BP coincident with a short-lived cooling event. A dwarf-shrub expansion and raised limnic productivity at 9600 BP suggest milder conditions and absence of sea ice. Relative sea level fell below present sea level at 9000 BP. A rapid vegetation change at 8800 BP suggests a temperature rise and a change to drier summer conditions, and the vegetation in the period 8800-8000 BP may be described as a dwarf-shrub and shrub tundra. Another abrupt vegetational succession at 8000 BP, possibly indicating increased winter precipitation, resulted in dominant shrub and dwarf-shrub tundra vegetation in the period 8000-7800 BP. It was concluded that the Late Weichselian-Early Holocene development on Skagi fits well with palaeoclimatic data from other parts of the North Atlantic region, indicating a close connection between deglacial ocean circulation changes and climatic conditions on Iceland. The results further suggest that the polar front was located south of Iceland in the period 11,300-10,900 BP, that its position was north of Iceland in late Allerød (10,900-10,600 BP), and that the Preboreal oscillation (c. 9800-9700 BP) most likely was associated with a southward migration of the polar front. In addition, the recording of transgressions on Skagi during cold events (the Younger Dryas and the Preboreal oscillation) implies that the Icelandic lithosphere is extremely sensitive to changes in volume of glacial ice, which suggests low asthenosphere viscosities below Iceland.