HOLOCENE PALEOCLIMATE CHANGE IN THE ADÉLIE BASIN, EAST ANTARCTICA (IODP EXP 318 SITE U1357)

Core U1357A (about 186 m long) was drilled in the Adélie Basin near the Wilkes Land (East Antarctica) during IODP Expedition 318. Sediments of core U1357A are composed primarily of laminated diatom ooze. Based on 28 AMS radiocarbon dates of bulk sediments, the sedimentation rate of core U1357A was calculated to average about 1.7 cm/yr during the Holocene. Biogenic opal contents were measured at 10-cm intervals (ca 5-year resolution) using the wet-alkaline sequential extraction method. The raw data were binned to calculate 5-points mean in order to minimize the noise. Because the sediments of core U1357A mainly consist of annual lamination couplets and the analyzed sediments were sampled regularly regardless cm-scale layering, we have to assess the seasonal difference between the light and dark layers of the biogenic opal record representative of paleoproductivity. Based on the comparison with the new gray scale from shipboard photographs as well as the shipboard L* values, biogenic opal contents are independent of the lamination color. After the deglacial termination at about 11 ka, the Adélie Basin became warm, and high productivity was maintained through the Hypsithermal interval. Productivity was reduced abruptly and distinctly at about 4-5 ka due to cooling, but resumed to increase at about 3 ka. Since then, late Holocene productivity decreased gradually toward the present. Biogenic opal variation during Holocene might be related to solar activity based on spectral analysis, showing 800 yr, 350 yr, 170 yr, 80~100 yr, 74 yr, and 54 yr periods.