Origin and consequences of cyclic ice rafting in the Northeast Atlantic Ocean during the past 130,000 years
Deep-sea sediment cores recovered from the Northeast Atlantic Ocean were examined in order to elucidate the influence of the Earth's orbital parameters on major ice rafting. Analyses of coarse-grained ice-rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal. Since 130,000 yr B.P., dropstone layers have been deposited each half period of a precessional cycle (11,000 ± 1000 yr). Ice rafting occurs during times of winter minimum/summer maximum insolation and summer minimum/winter maximum insolation. In the first case, high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter. In the second case, growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater. Both situations result in a southward penetration of polar water. Thus, the marine record of dropstones documents ice rafting not only during Weichselian stades but also during cold events within interstades. The regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes, not only in the region of the North Atlantic Ocean but also in remote areas such as the Pacific Ocean and the Antarctic.