Glacial/interglacial Cycles in the Norwegian Sea: Sedimentology, Paleoceanography, and Evolution of Late Pliocene to Quaternary Northern Hemisphere Climate

The long-term record of glacial/interglacial cycles indicates three major paleoceanographic regimes in the Norwegian Sea. The period since the first major glaciation over Scandinavia at 2.56 Ma is characterized by high-frequency, low-amplitude oscillations of ice-rafted debris inputs, a lowered salinity, and decreased carbonate shell production in surface waters as well as overall strong carbonate dissolution at the sea floor. These conditions indicate a more zonal circulation pattern in the Northern Hemisphere and a relative isolation of surface and bottom waters in the Norwegian Sea. The generally temperate glacial climate was only interrupted by episodic weak intrusions of warm Atlantic waters. These intrusions have been detected in considerable magnitude only at Site 644, and thus are restricted to areas much closer to the Norwegian shelf than during earlier periods. The interval from 1.2 to 0.6 Ma is characterized by an increase in carbonate shell production and a better preservation, as well as a change in frequency patterns of ice-rafted debris inputs. This pattern reflects increasing meridionality in circulation-strengthening contrasts in the Norwegian Sea between strong glaciations and warm interglacials. The past 0.6 Ma reveal high-amplitude oscillations in carbonate records that are dominated by the 100-k.y. frequency pattern. Glacial/interglacial sedimentary cycles in the ODP Leg 104 drill sites reveal a variety of specific dark lithofacies. These dark diamictons reflect intense iceberg rafting in surface waters fed by surges along the front of marine-based parts of the continental ice sheets in the southeastern sector of the Norwegian Sea and are associated with resuspension of reworked fossil organic carbon and strong dissolution at the sea floor. Piling up of huge iceberg barriers along the Iceland-Faeroe-Scotland Ridge might have partially blocked off surface water connections with the North Atlantic during these periods

Sedimentary facies of glacial-interglacial cycles in the Norwegian Sea during the last 350 ka

Sediment fluxes were highest in the Norwegian Sea during late glacial/early deglacial periods, i.e., at oxygen isotope transition 43, below transition 65, at various levels within stage 6, and below stage 9. Dark diamictons deposited at these times reflect intense iceberg rafting in surface waters fed by surges along the front of the marine-based parts of the continental ice sheets in the southeastern sector of the Norwegian Sea. The high organic carbon content (0.5–1.3%) in these layers reflects input from erosion of terrigenious matter-rich sediments outcropping on the shelves. Partial oxidation of organic matter and decreased deep-water renewal may explain the strong carbonate dissolution observed during these periods. Interglacial environments were strongly variable throughout the last 350 ka. Circulation patterns of stage 5e best resemble modern conditions, while stage 7 and 9 sediments record a much weaker Norwegian Current

Late Quaternary climatic events and sea-level changes recorded by turbidite activity, Dakar Canyon, NW Africa

The relationship of sea-level changes and short-term climatic changes with turbidite deposition is poorly documented, although the mechanisms of gravity-driven sediment transport in submarine canyons during sea-level changes have been reported from many regions. This study focuses on the activity of the Dakar Canyon off southern Senegal in response to major glacial/interglacial sea-level shifts and variability in the NW-African continental climate. The sedimentary record from the canyon allows us to determine the timing of turbidite events and, on the basis of XRF-scanning element data, we have identified the climate signal at a sub-millennial time scale from the surrounding hemipelagic sediments. Over the late Quaternary the highest frequency in turbidite activity in the Dakar Canyon is confined to major climatic terminations when remobilisation of sediments from the shelf was triggered by the eustatic sea-level rise. However, episodic turbidite events coincide with the timing of Heinrich events in the North Atlantic. During these times continental climate has changed rapidly, with evidence for higher dust supply over NW Africa which has fed turbidity currents. Increased aridity and enhanced wind strength in the southern Saharan–Sahelian zone may have provided a source for this dust

Paleoceanography and rotational block faulting in the Jurassic carbonate series of the Chiemgau Alps (Bavaria)

The Jurassic carbonate series of the Lechtal and Allgäu Nappes in the central part of the Northern Calcareous Alps reflect formation of orogen-parallel structures with swells and basins. Regional facies patterns display the morphologies of the various depositional environments. During the Middle Jurassic, an elongated swell evolved parallel to the overall structural strike in the central part of Lechtal Nappe, while in the southern part a basin started to subside. This configuration reflects the initial stage of rotational block faulting on the southern continental margin of the Tethys. Similar structural and facies settings were also established in the northern part of the Lechtal Nappe and in the southern Allgäu Nappe. Synsedimentary tectonics induced a variety of downslope sediment mass movements and increased facies differentiation on the slopes. In the upper section of the middle Jurassic sequences red nodular limestones with frequent intercalations of intraformational breccias and conglomerates indicate downslope sediment movements. During the Oxfordian, the Tethyan-wide deposition of radiolarites also covered the basin in the southern Lechtal Nappe. Contemporaneous deposition of pelagic radiolarian-bearing limestones dominated on the slope of the surrounding northern swell, while its peak was covered by a shallow water carbonate facies, e.g. a specific pseudopeloid and oolithic facies, which was also injected downslope into the pelagic facies. The Oxfordian to Tithonian section reveals a characteristic pelagic carbonate facies succession, e.g. with Protoglobigerina facies at the base, followed by aSaccocoma facies and a calpionellids facies on top. In the northern Lechtal Nappe and in the Allgäu Nappe various similar radiolarite basins with intersected swells were discovered

Evidence for a steeper Eemian than Holocene sea surface temperature gradient between Arctic and sub-Arctic regions

Sediment proxy data from the Norwegian, Greenland, and Iceland seas (Nordic seas) are presented to evaluate surface water temperature (SST) differences between Holocene and Eemian times and to deduce from these data the particular mode of surface water circulation. Records from planktic foraminiferal assemblages, CaCO3 content, oxygen isotopes of foraminifera, and iceberg-rafted debris form the main basis of interpretation. All results indicate for the Eemian comparatively cooler northern Nordic seas than for the Holocene due to a reduction in the northwardly flow of Atlantic surface water towards Fram Strait and the Arctic Ocean. Therefore, the cold polar water flow from the Arctic Ocean was less influencial in the southwestern Nordic seas during this time. As can be further deduced from the Eemian data, slightly higher Eemian SSTs are interpreted for the western Iceland Sea compared to the Norwegian Sea (ca. south of 70°N). This Eemian situation is in contrast to the Holocene when the main mass of warmest Atlantic surface water flows along the Norwegian continental margin northwards and into the Arctic Ocean. Thus, a moderate northwardly decrease in SST is observed in the eastern Nordic seas for this time, causing a meridional transfer in ocean heat. Due to this distribution in SSTs the Holocene is dominated by a meridional circulation pattern. The interpretation of the Eemian data imply a dominantly zonal surface water circulation with a steep meridional gradient in SSTs