Climatic and hydrographic variability in the late Holocene Skagerrak as deduced from benthic foraminiferal proxies

• Main Author: Brückner, Sylvia
• Other Authors: Mackensen, Andreas, Wefer, Gerold
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Bremen 2007
• Subjects: benthic foraminifera; stable isotopic composition; NAO; Skagerrak; deep-water renewal; microhabitat effect; vital effect; d13C; d18O; 550; 550 Earth sciences and geology; ddc:550; North Atlantic; North Atlantic oscillation
• Online Access: https://media.suub.uni-bremen.de/handle/elib/2485; https://nbn-resolving.org/urn:nbn:de:gbv:46-diss000109893

Two Holocene sediment cores from the southern flank of the Skagerrak are investigated for the stable oxygen and carbon isotopic composition of benthic foraminiferal tests and faunal assemblages. Core 225514 was recovered from 420 m and Core 225510 from 285 m water depth.The stable oxygen isotopic composition of Bulimina marginata tests in Core 225514 is demonstrated to indicate Skagerrak deep-water renewal during the last 1200 years. Since deep-water renewal is characterized by sudden dropsin temperature and salinity, and since δ18O values reflect both temperature and salinity changes, the influences of the two parameters have to be evaluated separately. By comparing the measured δ18O variability with a salinity-δ18O mixing line valid for marine to brackish Scandinavian waters, it was shown that salinity changes are responsible for maximal 9 % of the total δ18O variability. Correlationof temperature monitoring data with the North Atlantic Oscillation (NAO) index reveals that Skagerrak deep-water renewal is triggered by the negative phase of the NAO. During highly negative index phases very cold and calm conditions prevail over the North Sea. Central North Sea water masses are cooled down strongly and hence reach densities, which are higher than those of the deep Skagerrak water masses. Occasionally, these dense water masses start to cascade into the Skagerrak.The stable carbon isotopic composition of benthic foraminiferal tests is used to investigate the organic matter flux to the seafloor and the oxygen availabilitywithin the sediments as well as to approach microhabitat-corrected vital effects of four species. The δ13C values of Uvigerina mediterranea indicate that the flux of organic matter to the seafloor was relatively constant between AD 1500 and 1950 and increased after AD 1950. We suggest that this increase in organic matter flux to the seafloor results from hydro-climatic variability within the North Sea region. A persistently high NAO index during the 1980s and 1990s enhanced the influx of ...