BIOGENIC SEDIMENTS IN THE WEST CAROLINE BASIN, THE WESTERN EQUATORIALPACIFIC DURING THE LAST 330,000 YEARS

Primary productivity as well as new production have played an importan t role in the global carbon cycle during the late Quaternary. The mean organic carbon/nitrogen atomic ratio was 8.3 from the C4402 sediments in the West Caroline Basin, which indicates a limited contribution of terrigenous organic carbon to the organic matter in the sediments. Th e fluctuation of carbonate preservation shows that the accumulation ra te of organic carbon has reflected primary productivity. The results f rom sediment trap experiments which were carried out at Site C4402 ind icate that plankton bloom was characterized by a large influx of silic eous plankton, when organic carbon was effectively removed. Palaeoprod uctivity estimates calculated by using the formula of Sarnthein et al. (1988) would be plausible because the fluctuation pattern of such est imates correlates closely with changes in the accumulation rate of bio genic opal in the sediments. The primary productivity in the West Caro line Basin increased during Stage 2, Stage 3, late Stage 6, Stage 6/7 boundary and Stage 8. At a glance, the results are similar to other st udies that have reported higher glacial productivity in low-latitude r egions. However, some leads and lags are found between the West Caroli ne Basin and other areas of the equatorial Pacific and Atlantic. The s pectral analysis of MAR(Organic) indicates that the western equatorial Pacific reaches a maximum in MAR(Organic) approximately 7000 years be fore the maxima in the eastern Pacific. A regional variation of the re sponse of MAR(Organic) to the orbital forcing climatic condition sugge sts that the efficiency of the organic carbon pump may vary with longi tude in the equatorial Pacific. (C) 1998 Elsevier Science B.V. All rig hts reserved.