Molecular paleoclimatology: reconstruction of climate variabilities in the late Quaternary

Lipid class compounds were studied in the deep-sea surface sediments from the central Pacific across a latitudinal transect at 175°E (48°N-15°S) and a box core from the western tropical Pacific to discuss their utility as paleoclimatological indicators. Higher concentrations of C25---C35 n-alkanes were observed in the higher latitudes in the north Pacific. Their latitudinal distributions are similar to the spatial distributions of the observed soil dust concentrations observed in the central-north Pacific atmosphere, suggesting that the sedimentary C25---C35 n-alkanes are atmospherically transported from terrestrial higher plants, and can be used as an indicator of terrestrial input to ocean environments. Downcore distributions of total C25---C35 n-alkanes suggest that terrestrial input doubled over the western tropical Pacific at the LGM and decreased by a factor of two at the last deglaciation period in comparison with the Holocene. The latitudinal distributions of C17---C20 n-alkanes and pristane are higher in the high latitudes and equatorial region, probably reflecting the higher primary productivity in surface waters of these oceans. The downcore profiles of these compounds, as well as total organic carbon, long-chain alkenones and dinosterol suggest that biological production decreased significantly during the deglaciation period and slightly increased during the LGM compared with that of the Holocene. The downcore UK37 record suggests that the SST was almost constant over the last 20 000 y, which agrees well with the CLIMAP results and foraminifera δ18O, although it disagrees with results from coral Sr/Ca ratios and δ18O records.