Continuous late Neogene sediment sections from Site 907 on the Iceland Plateau and Sites 642, 643, and 644 on the Vøring Plateau were studied using stable isotope stratigraphy and sedimentological methods. Paleoclimatic and paleoceanographic changes have been placed in a time framework by using paleomagnetic reversals, biostratigraphic events, and isotope stratigraphic events as chronostratigraphic tools. The results show a general cooling of the Iceland-Norwegian Sea deep waters during the last 12 m.y., with major cooling events ~11.0 Ma and 6.4 Ma. At the Vøring Plateau, the oldest pulses of glacial ice-rafted debris (IRD) date to ~12.6 Ma, indicating that glaciers reached sea level as earl as the middle Miocene. The records of ice-borne deposits document a gradual intensification of glaciation from 7.2 to 6.0 Ma, which reflects the onset of small-scale glaciation in the Northern Hemisphere. The onset of large-scale Northern Hemisphere glaciation is dated at 2.75 Ma at the Vøring Plateau and 2.90 Ma at the Iceland Plateau, possibly reflecting different timing of growth of large-scale ice sheets in Greenland and Scandinavia. The middle Pleistocene climate shift (~0.9 Ma) is documented in both stable isotope stratigraphy and IRD deposition. The changes indicate a shift toward more extensive glacials of longer duration and the initiation of warmer interglacials with enhanced influx of Atlantic waters and ventilated deep waters. Within the Brunhes, deep-water formation apparently peaks during times of general climate deterioration and is not a linear response to global ice volume and sea-surface temperature. A general increase in planktonic delta 13C ~400 ka may reflect decreased global deep-sea carbonate preservation associated with the middle Brunhes climate transition.
Date of initial receipt: 10 July 1995
Date of acceptance: 7 December 1995
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