Intensification of Northern Hemisphere glaciations in the circum Atlantic region (3.5–2.4 Ma) – ice-rafted detritus evidence

Records of ice-rafted detritus (IRD) from Ocean Drilling Program Sites 644 and 907 in the Nordic Seas and Deep Sea Drilling Program Sites 610 and 607 in the North Atlantic Ocean are used to determine the growth and history of Northern Hemisphere glaciations spanning the interval from 3.6 to 2.4 Ma. The records document that the initiation of large-scale glaciation in the circum Atlantic region occurred stepwise between 3.5 and 2.4 Ma, with Greenland leading the other areas. The first major pulse of IRD occurs at 3.3 Ma suggesting a distinct expansion of the Greenland ice sheet. Progressive increases in IRD occur from 3.0 Ma, with a synchronous ice sheet development between the Greenland, Scandinavian and North American regions starting around 2.72–2.75 Ma. The regional records of IRD correspond to major trends in the oxygen isotope record, suggesting a tight connection between the record of global ice volume and evidence for expanding glaciers in the Northern Hemisphere. It appears as if widespread IRD distribution occurs when the global ice volume surpasses certain thresholds, similar to the late Quaternary situation.