The progressive intensification of northern hemisphere glaciation as seen from the North Pacific

Ocean Drilling Project (ODP) site 882 (50°22′N, 167°36′E) provides the first high-resolution GRAPE density, magnetic susceptibility, carbonate, opal and foraminifera (planktonic and benthic) stable isotopes records between 3.2 and 2.4 Ma in the Northwest Pacific. We observed a dramatic increase in ice rafting debris at site 882 at 2.75 Ma, which is coeval with that found in the Norwegian Sea, suggesting that the Eurasian Arctic and Northeast Asia were significantly glaciated from 2.75 Ma onwards. Prior to 2.75 Ma planktonic foraminifera δ¹⁸O records indicate a warming or freshening trend of 4°C or 2‰ over 80 ka. If this is interpreted as a warm pre-glacial Pliocene North Pacific, it may have provided the additional moisture required to initially build up the northern hemisphere continental ice sheet. The dramatic drop in sea surface temperatures (SST>7.5°C) at 2.75 Ma ended this suggested period of enhanced SST and thus the proposed moisture pump. Moreover, at 2.79 and 2.73 Ma opal mass accumulation rates (MAR) decrease in two steps by five fold and is accompanied by a more gradual long-term decrease in CaCO₃ MARs. Evidence from the Southern Ocean (ODP site 704) indicates that just prior to 2.6 Ma there is a massive increase in opal MARs, the opposite to what is found in the North Pacific. This indicates that the intensification of northern hemisphere glaciation was accompanied by a major reorganisation of global oceanic chemical budget, possibly caused by changes in deep ocean circulation. The initiation of northern hemisphere glaciation occurred in the late Miocene with a significant build up of ice on southern Greenland. However, the progressive intensification did not occur until 3.5–3 Ma when the Greenland ice sheet expanded to include northern Greenland. Following this stage we suggest that the Eurasian Arctic and Northeast Asia glaciated at 2.75 Ma, approximately 100 ka before the glaciation of Alaska (2.65 Ma) and 200 ka before the glaciation of the North East American continent (2.54 Ma).