Abstract
Waxing/waning of the ice sheets and the associated change in thermohaline circulation have played an important role in global climate change since major continental ice sheets appeared in the northern hemisphere about 2.75 million years ago. In the earliest glacial stages, however, establishment of the linkage between ice sheet development and ocean circulation remain largely unclear. Here we show new high-resolution records of marine isotope stage 100 recovered from deep-sea sediments on the Gardar Drift, in the subpolar North Atlantic. Results of a wide range of analyses clearly reveal the influence of millennial-scale variability in iceberg discharge on ocean surface condition and bottom current variability in the subpolar North Atlantic during marine isotope stage 100. We identified eight events of ice-rafted debris, which occurred mostly with decreases in sea surface temperature and in current components indicating North Atlantic Deep Water. These decreases are interpreted by weakened deep water formation linked to iceberg discharge, similarly to observations from the last glacial period. Dolomite fraction of the ice-rafted events in early MIS 100 like the last glacial Heinrich events suggests massive collapse of the Laurentide ice sheet in North America. At the same time, our early glacial data suggest differences from the last glacial period: absence of 1470-year periodicity in the interactions between ice sheets and ocean, and northerly shift of the ice-rafted debris belt. Our high-resolution data largely improve the picture of ice-sheet/ocean interactions on millennial time scales in the early glacial period after major Northern Hemisphere glaciation.
Highlights
Collapse of continental ice sheets, one of the major threats posed by global warming, made an impact on the global ocean circulation and climate system through the Pleistocene
Subsequent studies suggested that the millennialscale changes date back to Marine Isotope Stage (MIS) 100 around the intensification of Northern Hemisphere glaciation (NHG) (Bartoli et al, 2006; Becker et al, 2006; Bolton et al, 2010; Bailey et al, 2012, 2013)
Development of continental ice sheets in the circum-North Atlantic region was inferred by ice-rafted debris (IRD) records
Summary
Collapse of continental ice sheets, one of the major threats posed by global warming, made an impact on the global ocean circulation and climate system through the Pleistocene. Lines of evidence have demonstrated that such linkage between the ice sheets and the ocean circulation repeatedly occurred in millennial time scale, as represented by the last glacial Dansgaard-Oeschger (D-O) cycles and Heinrich events (e.g., Hemming, 2004; Clement and Peterson, 2008). Subsequent studies suggested that the millennialscale changes date back to Marine Isotope Stage (MIS) 100 around the intensification of Northern Hemisphere glaciation (NHG) (Bartoli et al, 2006; Becker et al, 2006; Bolton et al, 2010; Bailey et al, 2012, 2013). The millennial-scale changes were unclear in the carbon isotope records of benthic foraminifer (δ13Cbenthic) reflecting the bottom water conditions at least partly because of low data resolution. Paleoceanography at the onset of NHG should be improved by multiple data sources with higher time resolution
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