Late Quaternary paleoceanographic variations in the eastern Greenland Sea, Barents Sea and Spitsbergen fjords inferred by the foraminiferal assemblages and sedimentological records.

The Arctic area is responding more rapidly to global warming than most other areas on our planet. The identification of sedimentary systems and processes in the Arctic area allows the reconstruction of its palaeoclimatic and palaeoenvironmental evolution during the Quaternary period. This work consists of the study of three sites located in the Fram Strait (eastern Greenland Sea), in the western Spitsbergen Fjords and in the northwestern edge of the Barents Sea, corresponding with diverse geographical, morphological and oceanographical settings. These sites are all located along the main incoming pathway of the Atlantic Water (AW) into the Arctic area, allowing to reconstruct the oceanographical changes during the last 12 kyr BP, with a special focus on the last centuries. Thus, the overall aim of this PhD Thesis is to improve the knowledge of the centennial and decadal climatic variations and ocean circulation and to trace the AW impact into the Arctic area during the upper Pleistocene and Holocene. A multiproxy (e.g. planktic and benthic foraminifera, sediment lithology) investigation is applied to a long marine sediment core recovered from the Bellsund Drift depocenter and six short cores from Bellsund Drift, a coastal fjord and the Kveithola Trough. The sedimentary record of the Calypso piston core (GS191-01PC, 1647m water depth), records the Upper Pleistocene (12.05 to 11.7 kyr BP), and an expanded Holocene sequence (more than 5 m thick, 11.7 to 0.63 kyr BP). The millennial record of the Bellsund Drift indicates a general progressive increase of the bottom and superficial water temperature, due to the incoming of the warm AW and the decreasing of sea ice extent. In the same area, I also analysed a box-corer (20 cm length, 1647 m water depth), which records the climatic variations of the Modern Period (MP, 1890 A.D. to present). My results indicate a general warm increment during the entire MP, interrupted by short cold events of about ca. 5 years. In the Kongsfjorden-Krossfjorden glacial system, a tidewater glacier fjord, (western margin of Svalbard) I analysed a multi-corer (32 cm at 105.6 m water depth), which records the last 60 years. This ice-covered area shows a decrease of the ice influence not directly related to the AW inflow, but indicated by the dominance of the cold ArW species related to meltwater and the no increment in the AW species. Four multi-cores collected along the Kveithola Trough are also studied (between 8 and 38 cm of sediment recovered and at water depths ranging from 376 m to 159 m) and correspond with the last part of the Little Ice Age (LIA) and Modern Period (MP). The foraminiferal assemblages indicate the passage from colder to warmer conditions during the last 350 years, conditioned by the morphology and geographical position of the trough. The palaeoenvironmental evolution of the bottom and the surface water masses indicate multiyear and decadal variations between warm and cold periods during the last c.a. two centuries, related to the interaction between the polar superficial cold-water and the warm bottom AW. The foraminiferal assemblages demonstrate increasing temperatures, but still the dominance of Arctic species, which are related to the continuing retreat of the sea ice, the reduction in the albedo and further favouring heat of the ocean surface; and the increase of the air temperature amplifying the input of heat in the area.