South to north: Contrasting late-glacial and early-Holocene climate changes and vegetation responses between south and north Norway

Norway shows south-north climate and vegetation gradients today. Were there similar gradients during the late-glacial and early Holocene, 14,700-9000 years ago? A comparison was made along a south-north transect in Norway of plant-macrofossil reconstructions of past vegetation changes and independent summer temperature records derived from parallel chironomid data (C-Tjul). Three lake sites were selected with sediment cores with good chronological control. The importance of soil moisture is reflected by the reconstructed vegetation in relation to the temperature regime. Besides climate drivers, how important were intrinsic succession and competition in influencing vegetation patterns? Were migration delays significant, why and by how much? Oceanic climate in the late-glacial in south-west Norway resulted in snow-bed vegetation and glacier development in the Younger Dryas (YD). In contrast, the north was arid and continental, even into the early Holocene. Overall, temperatures were about 2 degrees C colder than in the south. The YD impact differed markedly between south and north Norway. In the south, cooling at c. 12,700 cal. yr BP was swift and marked by strong responses. In the north, there was no impact at the chronological start of the YD, but cooling occurred later about 12,450 cal. yr BP together with increased aridity. During the early Holocene, temperature and oceanicity increased progressively northwards as the North Atlantic Current became established. Birch woodland developed in the south about 660 years after the start of the Holocene, after about 1000 years on AndOya, and after about 1450 years in northernmost Norway. However, the 590 year lag in the south after C-Tjul reached 11 degrees C, the limiting temperature for tree-birch growth, decreased to 400 years in the north, as the birch tree-line kept pace with temperature rise. In the far north, a thermal maximum of 1 degrees C above today's mean July temperature and parallel vegetation development were recorded from 10,100 to 9370 cal. yr BP. On AndOya, temperatures exceeded present values by 1 degrees C after 9700 cal. yr BP. There was no detectable period of above modern temperatures further south before 9000 cal. yr BP.