Variability of the Arctic front during the last climatic cycle: application of a novel molecular proxy

Abstract

In the Nordic Seas, the Arctic front (AF) marks the boundary between the waters of the North Atlantic Drift/Norwegian Current and those of the Arctic domain. Long‐ or short‐term shifts in the position of the AF may affect climate conditions in the northern hemisphere. Arctic water masses are also the loci of modern open ocean convection; hence, defining these areas in the past is important for reconstructing and modelling ocean circulation and its variability. C37 alkenones are biomarkers for some algae of the Class Prymnesiophyceae (e.g. coccolitho‐phorids such as Emiliania huxleyi). These alga occur in most parts of the oceans, in ice‐free conditions, and are found nowadays throughout the Nordic Seas. We have related the sedimentary abundance of the tetraunsaturated C37 alkenone (C37:4) to two types of water masses in the Nordic seas. In locations affected by Atlantic water masses percentages of C37:4 are less than 5%, whereas in Arctic type water masses these increase to more than 5%. We propose that this observation can be used as a modern analogue to reconstruct the position of the AF in North Atlantic Quaternary sediments. Using this novel molecular proxy we can infer that the southward migration of the AF in the NE Atlantic reached ≈ 50 °N during the last glacial maximum (LGM), but perhaps only 60 °N during the Younger Dryas, and that ocean conditions free of sea ice prevailed throughout the Northern North Atlantic in summer.