Introduction 3 Background 6 Scientific objectives 10 Site summaries 30 Expedition synthesis 34 Preliminary scientific assessment 35 Operations 40 References

Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the participating agencies, Consortium for Ocean Leadership,

No abstract

This thesis is a geochemical, micropaleontological and sedimentological study of a sedimentary sequence from Site U1314, recovered during IODP Expedition 306, located in the Gardar Drift (south Iceland), in the subpolar North Atlantic. The main subject of this Thesis is the study of the climatic variations at different time-scales (orbital and suborbital) that took place during the period between 1.070.000 a 780.000 years , known as the Mid-Pleistocene Transition, the evolution of surface and deep circulation patterns, ice-sheet dynamics in the North Atlantic, and changes in different patterns of the water column (nutrients, salinity, temperature, etc.). We have elaborated a high-resolution record of stable oxygen and carbon isotopes from benthic and planktonic foraminifera, a faunistic analysis of radiolarian and planktonic foraminifera assemblages, a record of terrigenous material accumulation and several geochemical analyses on bulk sediment (elemental composition, biogenic opal, carbon components and P sequential extraction) and on planktonic foraminifera shells (Mg/Ca paleothermometry).Results obtained indicate a climatic variability centered mainly at high-frequency periods, shown by abrupt increases in the amount of terrigenous material in the sedimentary sequence, that are interpreted as ice-sheet advances toward the ocean. Linked to these terrigenous discharges, there are dramatic changes in the radiolarian and planktonic foraminifera assemblages, related to rapid oscillations in the physico-chemical properties of the surface waters that resulted from the transference of large amounts of freshwater from the continent to the ocean. These catastrophic events had a large impact on the surface and deep circulation patterns, recorded as rapid southward advances of polar water masses and reduced deep-water production in the Nordic Seas (Greenland, Iceland and Norway) and increased flow of southern Hemisphere source deep-waters in the North Atlantic.Results from the spectral analyses on the IRD, sea surface temperature reconstructions and planktonic δ 18 O records reveal frequencies centered at periods, of around 21000 and 11000 years. These cyclicities are related with a precession signal and its harmonics, and they have been observed in many marine climatic records at low-latitudes. This suggests that the climatic variability indicated by the surface proxies from our Site is driven by a low-latitude forcing transported by tropical convective processes, either atmospheric or oceanic, toward the subpolar North Atlantic. Paleotemperature estimates based on Mg/Ca values from Neogloboquadrina pachyderma sin. show evidences of rising temperatures during or following the IRD discharge which would accelerate ice-sheet retreat. Moreover, superimposed to this suborbital climate variability, we observe an evolution of the climatic system toward an increasing influence of the 100-kyr cycle on glacial-interglacial variability since ~ 950 ka. This reconfiguration is observed in our data set as a global increase in ice-vol...