THE PROGRESSIVE INTENSIFICATION OF NORTHERN-HEMISPHERE GLACIATION AS SEEN FROM THE NORTH PACIFIC

Ocean Drilling Project (ODP) site 882 (50 degrees 22'N, 167 degrees 36 'E) provides the first high-resolution GRAPE density, magnetic suscept ibility, carbonate, opal and foraminifera (planktonic and benthic) sta ble 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, suggesti ng that the Eurasian Arctic and Northeast Asia were significantly glac iated from 2.75 Ma onwards. Prior to 2.75 Ma planktonic foraminifera d elta(18)O records indicate a warming or freshening trend of 4 degrees C or 2 parts per thousand over 80 ka. If this is interpreted as a warm pre-glacial Pliocene North Pacific, it may have provided the addition al moisture required to initially build up the northern hemisphere con tinental ice sheet. The dramatic drop in sea surface temperatures (SST >7.5 degrees 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 op al mass accumulation rates (MAR) decrease in two steps by five fold an d is accompanied by a more gradual long-term decrease in CaCO3 MARs. E vidence from the Southern Ocean (ODP site 704) indicates that just pri or 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 intensifi cation of northern hemisphere glaciation was accompanied by a major re organisation of global oceanic chemical budget, possibly caused by cha nges 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 d id not occur until 3.5-3 Ma when the Greenland ice sheet expanded to i nclude northern Greenland. Following this stage we suggest that the Eu rasian Arctic and Northeast Asia glaciated at 2.75 Ma, approximately 1 00 ka before the glaciation of Alaska (2.65 Ma) and 200 ka before the glaciation of the North East American continent (2.54 Ma).