Preboreal onset of cold-water coral growth beyond the Arctic Circle revealed by coupled radiocarbon and U-series dating and neodymium isotopes

Cold-water coral mounds of Lophelia pertusa are widespread across the Scandinavian shelf, which was completely ice-covered during the Last Glacial Maximum between 22 to 18 ka BR Rapid deglacial melt-down of the Fennoscandian inland ice and the retreat of its ice-streams freed most of the shelf of ice by similar to 15 ka BR However, cold-water coral growth commenced only after the Pleistocene-Holocene transition at 11.65 ka BP, when modern-like climatic patterns and oceanographic conditions were established. A tight climatic coupling has been constrained with U-series ages. Coupled C-14 ages provide local reservoir ages from various gravity cores in a fjord-setting in Stjernsund at 70 degrees N and on the open shelf in Traenadjupet at 66 degrees N. Reinvestigation of earlier C-14 coral chronologies suggests that coral ecosystems widely established themselves across the entire 3000 km long Scandinavian shelf prior to similar to 10 ka BR The earliest occurrence of Madrepora oculata at similar to 2.4 ka BP suggests a late Holocene colonization of the Norwegian shelf, which is linked to a prominent mound growth hiatus in Traenadjupet (64 degrees N). Mound growth rates near the northern biogeographic boundary of L. pertusa with up to similar to 614 cm ka(-1) during certain growth periods are much higher than the previously reported fastest rates of similar to 220 cm ka(-1) from the Irish margin. Contemporaneous rapid fjordbasin sedimentation is slower with similar to 63 cm ka(-1). Matrix C-14 ages overlap with coral C-14 ages from the same horizon. This indicates rapid framework construction and efficient trapping of background sediment. Hiatuses are frequent in on-mound sediments and only short periods of coral growth are recorded. Coupled Delta C-14 and epsilon(Nd) values indicate a persistent Holocene inflow of the North Atlantic Current in Stjernsund, but also deglacial meltwater mixing during the early Holocene prior to similar to 9.5 ka BR Reservoir ages are overall close to the surface marine reservoir age, but Delta R is highly localized. (C) 2011 Elsevier Ltd. All rights reserved