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[MIS18-P14] Iceberg events in the high latitude North Atlantic during the early Pleistocene (MIS 93–91)
Glacial-interglacial cycles began after the increase in continental ice sheets in the Northern Hemisphere about 2.7 million years ago (Shackleton et al.1984). The glacial-interglacial cycles are orbital-scale climate changes caused by the insolation forcing (Milankovitch cycles) in the Northern Hemisphere (Hays et al.1976). During the last glacial period, however, abrupt (millennial-scale) climate changes (Dansgaard-Oeschger cycles) occurred (Dansgaard et al. 1993), and collapses of continental ice sheets (Heinrich events) caused severe cooling events (Heinrich, 1988). The abrupt climate changes are believed to have been caused by changes in the oceanic thermohaline circulation (Broecker, 1994). Although the abrupt climate changes unexplained by the Milankovitch cycles are well known in the last glacial period, such abrupt climate changes remain unclear in the early Pleistocene.
In this study, we performed XRD and IRD analyses of marine sediments recovered from IODP Site U1314 in the Gardar Drift of the subpolar North Atlantic to investigate the growth and collapse of the circum-North Atlantic ice sheets during the early Pleistocene. The marine sediments of IODP Site U1314 enable high-resolution analyses because of their very high sedimentation rates. Ohno et al. (2016) and Hayashi et al. (2020) performed high-resolution analyses using the same core and found that in the section from 2.9 to 2.5 Ma, repeated iceberg events on millennial time scales first occurred during the MIS 100 glacial. However, intervals among the iceberg events during the MIS 100 glacial were several times longer than intervals of Dansgaard-Oeschger events during the last glacial. In the section between 2.38 and 2.34 Ma (MIS 93–90) newly analyzed in this study, iceberg events were found during the MIS 92 glacial and the MIS 91 interglacial. In particular, the MIS 92 iceberg events show intermediate time scales between the MIS 100 glacial and the last glacial, suggesting that the climate system may have changed.
In this study, we performed XRD and IRD analyses of marine sediments recovered from IODP Site U1314 in the Gardar Drift of the subpolar North Atlantic to investigate the growth and collapse of the circum-North Atlantic ice sheets during the early Pleistocene. The marine sediments of IODP Site U1314 enable high-resolution analyses because of their very high sedimentation rates. Ohno et al. (2016) and Hayashi et al. (2020) performed high-resolution analyses using the same core and found that in the section from 2.9 to 2.5 Ma, repeated iceberg events on millennial time scales first occurred during the MIS 100 glacial. However, intervals among the iceberg events during the MIS 100 glacial were several times longer than intervals of Dansgaard-Oeschger events during the last glacial. In the section between 2.38 and 2.34 Ma (MIS 93–90) newly analyzed in this study, iceberg events were found during the MIS 92 glacial and the MIS 91 interglacial. In particular, the MIS 92 iceberg events show intermediate time scales between the MIS 100 glacial and the last glacial, suggesting that the climate system may have changed.