(Table 1) Abundance of selected diatom taxa in the mid-Pliocene of ODP Hole 167-1022A@en

Diatom assemblages from the middle part of the Pliocene (3.2-2.5 Ma) were investigated from Ocean Drilling Program Sites 1016, 1021, and 1022 in an effort to infer paleotemperature fluctuations off California. Diatoms are very sparse in virtually all of the samples that were examined from Sites 1016 and 1021. This is presumably because these sites were seaward (west) of the coastal zone of diatom productivity during the middle part of the Pliocene. Diatoms are relatively common in the vast majority of samples that were examined from Hole 1022A. Diatom assemblages are dominated by Chaetoceros spores (a coastal upwelling component), the cold-water (subarctic) taxa Neodenticula kamtschatica and its descendant Neodenticula koizumii, and Thalassionema nitzschioides, a temperate taxon that is typically found at the seaward edge of coastal upwelling zones. Paleotemperature interpretations, however, are not possible at this time because of the scarcity of comparative modern core-top data.本研究针对大洋钻探计划（Ocean Drilling Program）1016、1021及1022站位的上新世（Pliocene）中期（3.2~2.5 Ma）硅藻组合（diatom assemblages）展开分析，旨在推断加利福尼亚外海的古温度波动。1016与1021站位的全部检测样品中，硅藻几乎均极为稀少，推测是由于在上新世中期，这些站位位于硅藻生产力沿岸带的向海侧（西侧）。而1022A钻孔的绝大多数检测样品中，硅藻相对较为丰富，其组合以角刺藻（Chaetoceros）孢子（属于沿岸上升流类群）、冷水（亚北极）类群堪察加新齿藻（Neodenticula kamtschatica）及其演化后代小泉新齿藻（Neodenticula koizumii），以及柔弱菱形藻（Thalassionema nitzschioides）为主；其中柔弱菱形藻为温带类群，通常见于沿岸上升流带的向海边界。不过，由于缺乏可对比的现代岩芯表层数据，目前暂无法开展古温度解译工作。