Biogenic sediments in the West Caroline Basin, the western equatorial Pacific during the last 330,000 years

Primary productivity as well as new production have played an important 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. The fluctuation of carbonate preservation shows that the accumulation rate of organic carbon has reflected primary productivity. The results from sediment trap experiments which were carried out at Site C4402 indicate that plankton bloom was characterized by a large influx of siliceous plankton, when organic carbon was effectively removed. Palaeoproductivity estimates calculated by using the formula of Sarnthein et al. (1988) would be plausible because the fluctuation pattern of such estimates correlates closely with changes in the accumulation rate of biogenic opal in the sediments. The primary productivity in the West Caroline 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 studies that have reported higher glacial productivity in low-latitude regions. However, some leads and lags are found between the West Caroline Basin and other areas of the equatorial Pacific and Atlantic. The spectral analysis of MAR(Organic) indicates that the western equatorial Pacific reaches a maximum in MAR(Organic) approximately 7000 years before the maxima in the eastern Pacific. A regional variation of the response of MAR(Organic) to the orbital forcing climatic condition suggests that the efficiency of the organic carbon pump may vary with longitude in the equatorial Pacific. (C) 1998 Elsevier Science B.V. All rights reserved.