(Table 1) Calcareous nannofossil distribution at ODP Site 180-1109 from the Solomon Sea, western Pacific

The paleoceanography of the Solomon Sea for the last 195,000 years was investigated, based on the observations of 21 taxonomic groups of calcareous nannofossils in 144 samples taken from tocean drilling program (ODP) cores 1109A-1H and 1109C-2H. Oxygen isotope ratios in tests of the planktonic foraminifer Globigerinoides ruber allow us to assign the cores to oxygen isotope stages 7-1. Past sea-surface temperatures (SST) were estimated qualitatively using the composition of three Gephyrocapsa coccolith morphotypes; the high-, intermediate- and low-angel types that are classified based on the bridge angle of coccolith, can be used as proxies for warm, intermediate and cold temperature, respectively. Abundance of the high-angel type coccoliths increased and decreased during the interglacial and glacial periods, respectively. This tendency is consistent with the expected change of the Western Pacific Warm Pool (WPWP) development. However, a large shift in the abundance of the high-angle type coccolith recorded during early stage 3 did not correspond to the oxygen isotope record. The ratio of small (<2.5 µm) placoliths of Reticulofenetsra and Gephyrocapsa to the low-photic species was higher during stage 2 than late stage 3 and 1. As the reduced blanketed effect to the WPWP would cause an increase in the number of small placoliths, a reduction of the WPWP in stage 2 is indicated by the increase of small placoliths and by the lower SST deduced from the composition of the Gephyrocapsa morphotypes. The decreasing trend of small placoliths after ~40 ka is similar to the results reported in several previous studies in the surrounding regions of Australia.本研究针对所罗门海过去19.5万年的古海洋学特征开展系统性调查，分析了取自大洋钻探计划（Ocean Drilling Program, ODP）1109A-1H与1109C-2H岩芯的144个样品中的21个钙质超微化石（calcareous nannofossils）分类群。通过浮游有孔虫（planktonic foraminifer）红拟抱球虫（Globigerinoides ruber）壳体的氧同位素比值，可将上述岩芯归属于氧同位素7阶至1阶。 研究采用3种基于颗石桥角度划分的桥石藻属（Gephyrocapsa）颗石（coccolith）形态型——高角度型、中角度型与低角度型——定性估算古海表温度（sea-surface temperatures, SST），这三类形态型可分别作为暖温、中温与冷温环境的替代指标。高角度型颗石的丰度在间冰期与冰期分别呈现升高与降低的变化趋势，这一特征与西太平洋暖池（Western Pacific Warm Pool, WPWP）演化的预期变化相符。但在氧同位素3阶早期记录到的高角度型颗石丰度大幅偏移，却与氧同位素记录并不一致。 相较于氧同位素3阶晚期与1阶，氧同位素2阶期间，网石藻属（Reticulofenestra）与桥石藻属的小型（<2.5μm）颗石球（placoliths）相对于低光照层物种的丰度比值更高。由于西太平洋暖池的遮蔽效应减弱会导致小型颗石球数量增加，因此小型颗石球丰度的升高以及基于桥石藻形态型推算得到的较低海表温度，均指示氧同位素2阶时期西太平洋暖池出现收缩。约4万年后小型颗石球丰度的下降趋势，与澳大利亚周边区域多项既往研究的结果一致。