Stable isotope composition of Neogene planktonic foraminifera from ODP Leg 130 sites

We produced a preliminary record for shallow-dwelling planktonic foraminifer d18O at Site 807 for the late Pleistocene, early Pliocene, and early Miocene. Site 807 d18O values between 4 and 5 Ma average 0.75 per mil more than Holocene values and show an average variation of 0.5 per mil. For the early Pliocene, peak maximum d18O at Site 807 attain values equivalent with the last glacial maximum whereas peak minimum d18O were never less than Holocene d18O. Shallow-dwelling planktonic d18O at Site 807 between 16 and 24 Ma average more than 1.0 per mil more positive than Holocene d18O and exhibit 0.5 per mil average amplitude. Assuming that the global ice budget for the early Pliocene and early Miocene was restricted to Antarctica, it is difficult to attribute the very positive Site 807 d18O for these intervals to ice on Antarctica. Site 807 d18O for these intervals more likely reflect sea-surface temperatures cooler than at present, sea-surface salinity greater than at present, increased dissolution, or some combination of these changes.本研究为807站位（Site 807）晚更新世（late Pleistocene）、早上新世（early Pliocene）及早中新世（early Miocene）时期的浅居浮游有孔虫（shallow-dwelling planktonic foraminifer）d18O建立了初步测试记录。807站位4~5 Ma区间内的d18O平均值较全新世（Holocene）偏高0.75‰，平均波动幅度为0.5‰。针对早上新世时段，807站位的d18O峰值最大值可与末次冰盛期（last glacial maximum）的数值相当，而其峰值最小值从未低于全新世d18O水平。807站位16~24 Ma区间内的浅居浮游有孔虫d18O平均值较全新世偏高1.0‰以上，平均波动幅度为0.5‰。若假设早上新世及早中新世的全球冰量仅局限于南极大陆，则难以将该时段807站位的极高d18O值归因于南极冰盖的影响。该时段807站位的d18O值更可能反映了当时海表温度（sea-surface temperatures）低于现代、海表盐度（sea-surface salinity）高于现代、溶解作用（dissolution）增强，或是上述多种变化的共同作用。