Dinoflagellate cysts and paleo-climatic and paleo-hydrologic evolution of the North Atlantic Ocean throughout the last climatic cycle

Dinoflagellate cyst analyses of Quaternary sediments from the North Atlantic Ocean has allowed here to document high climatic and hydrologic variability of this geographical area throughout the last 130,000 years. To better evaluate the amplitude of this variability, dino-cyst data were used as a semiquantitative and quantitative (transfer functions) tool and systematically correlated to the others geochemical, physical and and/or micro-paleontologic available proxies. Our results show that marked oscillations characterise the studied records. During the last glacial period, these oscillations closely reproduce the high variability initially observed in polar ice-sheet cores (Dansgaard-Oeschger cycles) but also in marine sediments (especially depicted by Heinrich events). The multi-location character of the study (IMAGES cores) provides information about the latitudinal evolution of the sea-surface environments and reveals an atypical response of the Nordic seas (Norwegian sea) between 50,000 and 20,000 years. Our results show evidences of the North-Atlantic Drift penetration in sub-arctic basins during Heinrich events (HL1 to HL5), yet contemporaneous of massive ice-sheet decays. Such evidence is also detected during the Last Glacial Maximum marked by a maximum extension of the polar ice-sheets. Concerning the Last Interglacial Complex period, stratigraphically correlated to the Marine Isotopic Stage 5 (130-74 ka), our data depict contrasted climatic events that can be identified on the regional scale. The Last Interglacial Period, the most recent analogue of the present climate, is here characterised in a new perspective. Three climatic phases have been identified in a general trend of reduced climate variability. (author)