Arctic Ocean warmings from the last glaciation to the present : implementing and assessing the reliability of planktic foraminiferal paleoreconstructions

Abstract

The aim of the PhD study was to use planktic foraminifera to elucidate paleoceanographic variability and the preservation state of calcium carbonate in the eastern Fram Strait throughout the last 30,000 years. Sediment cores were studied using a multiproxy approach which included analyzing planktic and benthic foraminiferal fauna distribution patterns, measurements of stable isotopes (δ18O, δ13C), grain size analysis, IRD counts, and chemical analysis of bulk sediment. In addition, mean shell weight records combined with fragmentation indices were applied. Three time periods representing important oceanographic changes in the Fram Strait were investigated with a high temporal resolution. The results show that the Atlantic water inflow governed the oceanographic development and had an important influence on the preservation state of calcium carbonate in the Fram Strait. The best preserved planktic foraminifera assemblages during the last 30,000 years were found during the Last Glaciation Maximum. Some minor dissolution events occurred during the Last Glacial Maximum as response to seasonally changing physical oceanographic parameters, sea ice formation, increased surface productivity, and melt water pulses. During the deglaciation and the Holocene, the preservation state of carbonates generally deteriorated. This trend was interrupted at 10,800-8000 BP, where the preservation of planktic foraminifera markedly improved. Changes in preservation are related to the extent and influence of the Arctic water and the marginal ice zone (MIZ) and its associated high organic productivity in the surface waters. During the last century, the preservation of small subpolar species improved. This coincided with distinctly increased sedimentation rates in the eastern and central Fram Strait. This study of planktic foraminifera preservation has shown that carbonate dissolution is a common phenomenon in the Fram Strait and should be considered in paleoreconstructions based on planktic foraminifera fauna.