NEOGENE-QUATERNARY VARIATIONS OF THE POLE-EQUATOR TEMPERATURE-GRADIENT OF THE SURFACE OCEANIC WATERS IN THE NORTH-ATLANTIC AND NORTH PACIFIC

The deep sea drilling core samples and published data of the Deep Sea Drilling Project and Ocean Drilling Program serve as the bases for thi s study. Original methods for paleotemperature interpretation of foram iniferal and oxygen isotopic data are suggested. For several Neogene-Q uaternary time-slices, the surface and near-surface paleotemperatures of the high and low latitudes in the North Atlantic and North Pacific are evaluated. During the Neogene, the 'Pole-Equator' gradient of the surface water mass at different depths tended to increase. It increase d by 8 degrees C at the oceanic surface, by 11.5 degrees C at the dept h of 50 m, by 15.5 degrees C at the depth of 100 m and by 11.5 degrees C at the depth of 200 m. This is related to the progressive cooling i n the high latitudes during Neogene-Quaternary. Maximum gradient varia tions are observed at the depth of 100 m resulting from thermocline on set and evolution. Our data suggest that the first sharp increase of g radient by 4-6 degrees C occurs between 10-5 Ma, and the second one (a lso 4-5 degrees C) during the Middle-Late Pliocene. These abrupt chang es correspond to the intensification of the oceanic circulation caused by the evolution of Neogene glaciation. In the Quaternary, the temper ature gradient slightly decreased. During the Last Glacial maximum, th e gradient was less than those observed during the Last Interglacial o ptimum and now. (C) 1998 Elsevier Science B.V. All rights reserved.