Millennial-scale iceberg surges after intensification of Northern Hemisphere glaciation

Iceberg discharges from continental ice sheets are widely believed to have exerted a great influence on global climate, but an iceberg discharge regime in early glacial periods after intensification of Northern Hemisphere glaciation (NHG) remains largely unclear. Here we present high-resolution rock magnetic records during the period from 2.1 to 2.75 Ma after intensification of NHG, reconstructed from the subpolar North Atlantic. Although the establishment of the middle Pliocene chronology of North Atlantic sediments is often a serious problem, we overcame it based on findings concerning the properties of magnetic susceptibility and natural gamma radiation. Reconstructed rock magnetic records indicate that millennial-scale iceberg surges were dominant features in the early glacial periods. Additionally, the millennial-scale iceberg surges occurred within glacial stages during intervals when ratios of global oxygen isotope stack from benthic foraminifera (LR04 δ¹⁸O stack) surpassed approximately 3.5‰. These are comparable to the climatic and environmental changes in Pleistocene glacial periods as represented by last glacial Dansgaard-Oeschger cycles, suggesting that continental ice sheets have oscillated and calved icebergs in a similar manner since intensification of NHG.