Benthic foraminifera and sediment grain size variability at intermediate water depths in the Northeast Atlantic during the late Pliocene-early Pleistocene

Sedimentological and faunal records from the transitional period marking th e onset of widespread northern hemisphere glaciation have been investigated at Ocean Drilling Program Site 984. The late Pliocene interglacial sedimen ts of the northeast Atlantic are carbonate rich and show evidence of vigoro us bottom water circulation at intermediate water depths. Contrasting this, the late Pliocene glacial sediments are characterised by carbonate dissolu tion and slower bottom current velocities. Weak or "leaky" Norwegian Sea ov erflows, undersaturated with respect to carbonate, influenced this region d uring the late Pliocene glacials. The early Pleistocene pattern of intermed iate water circulation appears to have changed radically in the northeast A tlantic. At this time, interglacial carbonate values and inferred bottom cu rrent velocities are low. This suggests slow-flowing, undersaturated Norweg ian Sea water bathing the site. The overflow increased during the early Ple istocene interglacials as the exchange between the Atlantic and Norwegian-G reenland Seas improved. The most significant feature of the early Pleistoce ne glacials is the increase in inferred bottom current velocity. These chan ges reflect a switch in deep North Atlantic convection to shallower depths during glacial periods, possibly in a manner similar to the increasing cont ribution of glacial intermediate water to the North Atlantic during the lat e Pleistocene glacials. Our results suggest that the late Pleistocene clima te variability of the North Atlantic is a pervasive feature of the late Pli ocene-early Pleistocene record. (C) 2000 Elsevier Science B.V. All rights r eserved.