Dinoflagellate cyst counts of sediment core GIK23071-3

Marine sediments from the Vøring Plateau (Norwegian Sea) have been studied for their dinoflagellate cyst (dinocyst) and foraminiferal content in order to reconstruct sea-surface conditions in the eastern Norwegian Sea during Marine Isotope Stage (MIS) 5e. In combination with stable oxygen isotope and ice rafted detritus (IRD) data, the variations in foraminiferal and dinocyst assemblage composition reflect a stepwise transition from the final phase of deglaciation (Termination II) into typical interglacial conditions. This stepwise change is repeated subsequently during the cooling conditions of glacial inception towards MIS 5d. The interval studied is characterized by relatively high abundances of Bitectatodinium tepikiense, in comparison to present-day values in the area, indicating a larger seasonal temperature amplitude with enhanced surface water stratification during MIS 5e. The important occurrence of the warm-temperate dinocyst Spiniferites mirabilis s.l. concurrent with subpolar foraminifers Turborotalita quinqueloba, Globigerina bulloides, and Globigerinita glutinata reveals that most pronounced interglacial marine conditions prevailed in the area just prior to the transition towards MIS 5d. The late stratigraphic position of this phase in the interglacial is verified by comparison with dinocyst data from south of Iceland, manifesting its over-regional implication. Besides the good agreement in dinocyst and foraminiferal assemblage changes, the variations in and between both fossil assemblages also point to the existence of some significant surface water variability in the eastern Norwegian Sea during MIS 5e.

Grain size distribution, carbon content and wet bulk density of sediment cores in the equatorial Atlantic and the Norwegian Sea

Near-surface sediments from the equatorial east Atlantic and the Norwegian Sea exhibit pronounced shear strength maxima in profiles from the peak Holocene and Pleistocene. These semi-indurated layers start to occur at 8-102 cm below the sediment surface and can be explained neither by the modal composition nor by the effective overburden pressure of the sediments. However, scanning electron microscope and microprobe data exhibit micritic crusts and crystal carpets, which are clearly restricted to (undisturbed) samples from indurated layers and form a manifest explanation for their origin. The minerals precipitated comprise calcite, aragonite, and in samples more proximal to the African continent SiO2 needles, and needles of as yet unidentified K-Mg-Fe-Al silicates, crusts of which dominate the indurated layers in the Norwegian Sea. By their stratigraphic position in deep-sea sediments the carbonate-based shear strength maxima are tentatively ascribed to dissolved adjacent pteropod layers from the early Holocene and hence to short-lived no-analogue events of early diagenesis. Possibly, they have been controlled by a reduced organic carbon flux, leading to increased aragonite preservation in the deep sea.

Database of the GLAMAP project

A uniform chronology for foraminifera-based sea surface temperature records has been established in more than 120 sediment cores obtained from the equatorial and eastern Atlantic up to the Arctic Ocean. The chronostratigraphy of the last 30,000 years is mainly based on published d18O records and 14C ages from accelerator mass spectrometry, converted into calendar-year ages. The high-precision age control provides the database necessary for the uniform reconstruction of the climate interval of the Last Glacial Maximum within the GLAMAP-2000 project.

Glacial North Atlantic: Sea surface conditions reconstructed by GLAMAP 2000

The response of the tropical ocean to global climate change and the extent of sea ice in the glacial nordic seas belong to the great controversies in paleoclimatology. Our new reconstruction of peak glacial sea surface temperatures (SSTs) in the Atlantic is based on census counts of planktic foraminifera, using the Maximum Similarity Technique Version 28 (SIMMAX-28) modern analog technique with 947 modern analog samples and 119 well-dated sediment cores. Our study compares two slightly different scenarios of the Last Glacial Maximum (LGM), the Environmental Processes of the Ice Age: Land, Oceans, Glaciers (EPILOG), and Glacial Atlantic Ocean Mapping (GLAMAP 2000) time slices. The comparison shows that the maximum LGM cooling in the Southern Hemisphere slightly preceeded that in the north. In both time slices sea ice was restricted to the north western margin of the nordic seas during glacial northern summer, while the central and eastern parts were ice-free. During northern glacial winter, sea ice advanced to the south of Iceland and Faeroe. In the central northern North Atlantic an anticyclonic gyre formed between 45° and 60°N, with a cool water mass centered west of Ireland, where glacial cooling reached a maximum of >12°C. In the subtropical ocean gyres the new reconstruction supports the glacial-to-interglacial stability of SST as shown by CLIMAP Project Members (CLIMAP) [1981]. The zonal belt of minimum SST seasonality between 2° and 6°N suggests that the LGM caloric equator occupied the same latitude as today. In contrast to the CLIMAP reconstruction, the glacial cooling of the tropical east Atlantic upwelling belt reached up to 6°-8°C during Northern Hemisphere summer. Differences between these SIMMAX-based and published U37[k]- and Mg/Ca-based equatorial SST records are ascribed to strong SST seasonalities and SST signals that were produced by different planktic species groups during different seasons.