Holocene sea surface conditions in the western North Atlantic: Spatial and temporal heterogeneities

Holocene records of sea surface conditions in the western Nordic seas were obtained from quantitative reconstructions based on dinoflagellate cyst assemblages. Two sediment cores from the east Greenland and the north Iceland shelves provide a detailed account of the long‐ and short‐term dynamics of the opposing flows of Arctic versus Atlantic waters. Both marker species and quantitative reconstructions depict an overall trend toward warmer winter temperatures, saltier surface waters, and decreased sea ice extent. The latter is supported by a close relationship between relative abundances of an Atlantic dinocyst species, Nematosphaeropsis labyrinthus , and ice‐rafted debris (IRD) records. We propose that the late Holocene increased IRD delivery in the Denmark Strait region was primarily induced by a combination of less extensive sea ice cover under increased Atlantic water inflow and sustained iceberg calving tied to the readvance of the Greenland ice sheet. Our records thus suggest diminishing polar water supplies throughout the Holocene, although the timing of regime changes differs between the western and eastern sides of the Denmark Strait. Finally, comparison of our records with a core from southern Greenland points to very heterogeneous sea surface conditions in the western North Atlantic, which could be explained by the decoupled dynamics of the two Irminger Current branches. Similarities between the southern Greenland marine record and a continental record nearby suggest a close coupling with atmospheric processes, reminiscent of a North Atlantic Oscillation–like climate pattern.