LEG 151

North Atlantic Arctic Gateways I

The Arctic and subarctic areas exert major influences on global climate and oceanic systems. The high northern latitude oceans directly influence the global environment through the formation of permanent and seasonal ice cover, the transfer of sensible and latent heat to the atmosphere, deep- water formation, and deep-ocean ventilation, which control or influence both oceanic and atmospheric chemistry.

During the Arctic summer of 1993, JOIDES Resolution, accompanied by the Finnish icebreaker MSV Fennica, recovered ODP's first scientific drill cores from the eastern Arctic Ocean, including material which records the earliest history of the connection between the North Atlantic and Arctic oceans, the onset of glacial climate in the Arctic, and the inception of abundant sea-ice formation and sediment ice rafting, and evidence for massive ice caps on the Arctic Ocean margin during certain glaciations. Sediments were recovered from three sites north of 80¡N on the Yermak Plateau (Site 910 to Site 912), two sites in Fram Strait (Sites 908 and 909), one site on the northeastern Greenland margin (Site 913), and one site on the Iceland Plateau (Site 907).

The region between Greenland and Norway first formed a series of isolated basins, sometimes with restricted deep circulation, which eventually joined and allowed deep and surface Arctic Ocean water to invade the region. Deep-water flow from the Arctic, and deep-water production in the Nordic seas, did not occur until the latest part of the Miocene. The onset of glacial climate in the Arctic and the inception of abundant sea-ice formation and sediment ice rafting occurred near the late Miocene/Pliocene boundary. At all seven Leg 151 sites, the Pliocene and Quaternary interval is marked by evidence of ice, with the first significant dropstones appearing near the late Miocene/Pliocene boundary.

On the Yermak Plateau in the Arctic Ocean, drilling provided evidence for massive ice caps on the Arctic Ocean margin during certain glaciations. The plateau is a locus of sedimentation in the Pliocene and Quaternary, possibly reflecting melting of a sediment-laden pack ice transported to the plateau by Arctic surface circulation. Drilling also recovered evidence for at least one advance of the Svalbard/Barents Sea ice sheet out over the Yermak Plateau in the late Pleistocene. This extension of the ice sheet northwestward will provide important constraints for ice models of the Pleistocene.