LATE CENOZOIC HISTORY OF THE POLAR NORTH ATLANTIC: RESULTS FROM OCEAN DRILLING

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DSDP/ODP drilling in the northern North Atlantic reveals that so far the onset of northern hemisphere cooling deduced from the occurrence of ice-rafted debris (IRD) in deep-sea sediments can be traced back to the middle Miocene. The Greenland ice sheet has probably the longest history on the northern hemisphere. Leg 151 site 909 (Fram Strait) recovered a unique continuous sediment record dating from early/middle Miocene. The composition of the coarse fraction indicates that the oldest IRD pulses are documented around 14 Ma in the Fram Strait (site 909) and around 12.6 Ma on the Vöring Plateau (leg 104, site 642) in the Norwegian–Greenland Sea. Fram Strait site 909 indicates a further stepwise increase of northern hemisphere cooling by serveral IRD pulses during late Miocene (between 10.8 and 8.6 Ma, around 7.2, 6.8 and 6.3 Ma), which ultimately led to a drastic intensification of northern hemisphere glaciation during Plio–Pleistocene. The deep-sea sediment records show that Plio–Pleistocene strengthening of IRD pulses have been observed since approximately 4.0 Ma in the westernmost Norwegian–Greenland Sea and Labrador Sea; by contrast, strengthening of IRD pulses are observed at approximately 3.2–2.7 Ma on the eastern side of the Norwegian–Greenland Sea, including the Barents Sea margin. Sediment composition and physical properties of the drilled, mostly terrigenous sections reveal that orbital parameters have controlled major aspects of shallow and deep-water environments with frequency domains related to 41 ka periods of obliquity dominant in the pre-glacial Miocene, Pliocene and early Quaternary and to 100 ka periods of eccentricity dominant during the past 600,000–700,000 years. The stratigraphy of ice-rafted material reveals a frequently and rapidly changing history of the dynamics of various segments in ice sheets around the Norwegian–Greenland Sea. It is particularly evident from the composition of the ice-rafted material that the Eurasian ice sheets delivered IRD to the eastern part of the Norwegian–Greenland Sea, whereas Greenland source areas are represented in the drill sites of the east Greenland continental margin and in the Labrador Sea. The stratigraphic sequences on the Yermak Plateau suggest that the Svalbard ice sheet may have extended far to the north prior to oxygen isope stage 16 but not since then. Invasions of temperate Atlantic waters during interglacials can be observed as short-lived and rather irregular events. It never reached the area off eastern Greenland except during the Pliocene interval, when tundra floras were able to develop on north-eastern Greenland and planktonic foraminifers suggesting the presence of temperate water masses in the Fram Strait as been documented in the drill sites from the Yermak Plateau.