Coarse-fraction composition in sediments of ODP Leg 104

Coarse-fraction studies of sediments recovered during ODP Leg 104 are used to reconstruct paleoclimatic and paleoceanographic environments on a time scale of 0.1 to 0.5 m.y. for the past 20 Ma. These investigations suggest that relatively warm climates and isolated deep water conditions prevailed prior to 13.6 Ma and between 5.6-4.8 Ma. The first major deep water outflow from the Norwegian-Greenland Sea into the North Atlantic took place at about 13.6 Ma. Progressive cooling linked to increased deep water renewal in the Norwegian-Greenland Sea appears to have occurred between 13.6-5.6 Ma and 4.8-3.1 Ma. A major onset of ice-rafted debris is recorded at 2.56 Ma. Terrigenous coarsefraction components show important fluctuations with two major peaks during the past 0.8 Ma.

Mineralogy of ODP Leg 104 holes

The mineralogical and geochemical study of samples from Sites 642, 643, and 644 enabled us to reconstruct several aspects of the Cenozoic paleoenvironmental evolution (namely volcanism, climate, hydrology) south of the Norwegian Sea and correlate it with evolution trends in the northeast Atlantic. Weathering products of early Paleogene volcanic material at Rockall Plateau, over the Faeroe-Iceland Ridge and the Voring Plateau indicate a hot and moist climate (lateritic environment) existed then. From Eocene to Oligocene, mineralogical assemblages of terrigenous sediments suggest the existence of a warm but somewhat less moist climate at that time than during the early Paleogene. At the beginning of early Miocene, climatic conditions were warm and damp. The large amounts of amorphous silica in Miocene sediment could indicate an important flux of silica from the continent then, or suggest the formation of upwelling. Uppermost lower Miocene and middle to upper Miocene clay assemblages suggest progressive cooling of the climate from warm to temperate at that time. At the end of early Miocene, hydrological exchanges between the North Atlantic and the Norwegian Sea became intense and gave rise to an important change in the mineralogy of deposits. From Pliocene to Pleistocene, the variable mineralogy of deposits reflects alternating glacial/interglacial climatic episodes, a phenomenon observed throughout the North Atlantic.

Ice rafted debris and reconstructed sea surface temperature of ODP Hole 104-642B

The mid-Piacenzian warm period (3.264-3.025 Ma) of the Pliocene epoch has been proposed as a possible reference for future warm climate states. However, there is significant disagreement over the magnitude of high latitude warming between data and models for this period of time, raising questions about the driving mechanisms and responsible feedbacks. We have developed a new set of orbital-resolution alkenone-based sea surface temperature (SST) and ice rafted debris (IRD) records from the Norwegian Sea spanning 3.264-3.14 Ma. The SSTs in the Norwegian Sea were 2-3?°C warmer than the Holocene average, likely caused by the radiative effect of higher atmospheric CO2 concentrations. There is notable obliquity-driven SST variability with a range of 4?°C, shown by evolutive spectra. The correlation of SST variability with the presence of IRD suggests a common climate forcing acting across the Nordic Seas region. Changes of the SST gradient between the Norwegian Sea and North Atlantic sites suggest that the subpolar gyre was at least as strong as during the Holocene, and that the northward heat transport by the North Atlantic Current was comparable.