Föstudagserindi Jarðvísindastofnunar og Norræna eldfjallasetursins 20. mars 2026 - Lovísa Birgisdóttir (independent researcher, Reykjavík, Iceland)

Útdráttur:

Along a core transection at 70°N, from the eastern side of the Jan Mayen Ridge to the western side of the Kolbeinsey Ridge, investigations were carried out on the paleo-oceanographic variability of the Iceland Sea during the last approximately 550,000 years. Five to seven relatively well-correlatable sequences of clayey, quartz-rich sediments can be distinguished from layers rich in foraminifera.

A stratigraphic classification was achieved using oxygen isotope analyses from two sediment cores. The occurrence of the benthic foraminifer Pullenia bulloides was used to define the boundary between isotope stages 4 and 5. Volcanic activity in nearby volcanic regions (Jan Mayen, Iceland, Eggvin Bank) is recorded in well-correlatable tephra layers, for example in oxygen isotope stages 1 (~11,000 years), 2 (~14,000 years), 5 (~127,000 years), 7 (~211,000 and ~228,000 years), 8 (~272,000 years), and 11 (~400,000 years).

Temporal variability is reflected in the calcium carbonate content, which documents a complex interaction between different water masses and allows conclusions about increased productivity and preservation of the material. The calcium carbonate content generally decreases westward. Apparently, the full influence of the cold water masses of the East Greenland Current is only evident west of the Kolbeinsey Ridge. In that region, the weight percentages of quartz are generally higher. Quartz-free zones occur only in stage 11 in core 23243 and in stage 5e in the four eastern cores.

The complete absence of carbonate before 330,000 years BP coincides with clayey grey/green/red lithofacies sequences. This may indicate that during the older glacial periods (until about 330,000 years BP) the deep water was particularly corrosive and dissolved the existing calcareous skeletal material. It is also possible that the Iceland Sea was completely ice-covered during these periods, which would have prevented the production of calcareous shells. For the younger glacial periods (since about 300,000 years BP), it is assumed that the Iceland Sea was at least seasonally ice-free, allowing limited biological production.

A maximum influence of warm North Atlantic water masses is documented during stage 11 (about 423,000–362,000 years BP) by very high calcium carbonate and foraminiferal contents and by the absence of ice-rafted material (quartz, rock fragments, feldspar, heavy minerals, and mica) in the three eastern cores. A similar pattern appears in isotope stage 5e, though less pronounced in the Holocene.

Different sedimentation rates probably reflect a complex interaction between bathymetry (bottom currents and selective dissolution) and migrating frontal systems of highly variable water masses in this region (nutrient-richer, warmer water leading to higher

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