Reconstruction of mid- to late-Holocene winter temperatures in the Skagerrak region using benthic foraminiferal Mg/Ca and δ 18 O

Abstract

Reconstruction of Skagerrak deep-water renewal is used to assess regional changes in winter thermal conditions over the past 6800 years. Changes in winter climate conditions from the Skagerrak region are in turn linked to shifts in Holocene large-scale atmospheric circulation patterns prevailing over northern Europe. We use Melonis barleeanus Mg/Ca from two sediment cores in the central Skagerrak to reconstruct temperature of Skagerrak intermediate water, representing the warm season temperature variability, and deep water, for monitoring Skagerrak deep-water renewal, reflecting the winter temperature variability. In addition, M. barleeanus δ¹⁸O is used from the deeper core to reconstruct salinity, also monitoring the deep-water renewal. Our results show that the Skagerrak deep-water experienced phases of particularly enhanced renewal during the mid-Holocene reflecting severe winter conditions, followed by a general shift to reduced renewal as a consequence of milder winter conditions over the North Sea around 3500 cal. yr BP. The late-Holocene shift was most likely related to the onset of a regime with intensified winter westerly winds directed toward northern Europe and an increased inflow of North Atlantic water into the Skagerrak–North Sea reflecting more maritime climate conditions. On millennial scale, cold phases in our deep-water records match with low winter precipitation phases in western Norway. They are associated with distinct increases in ice rafted debris (IRD) in North Atlantic sediments, suggesting that phases of iceberg discharge in the Atlantic were associated with cold and dry winter conditions over northern Europe. Interestingly, the cold event centered around 5900 cal. yr BP appears to be only associated with winter variability, while the following one at 4200 cal. yr BP is documented in our winter record, as well as in records related to warmer seasons.