Calcareous nannofossils, bulk and benthic foraminifera stable isotope from ODP Hole 121-756C@en

The Eocene-Oligocene transition (EOT, ~34 Ma) is marked by changes in calcareous nannofossil assemblages and coincides with variations in sea-surface temperature and nutrient availability. During the EOT, calcareous nannofossil assemblages underwent an abrupt turnover with a permanent decline of warm-oligotrophic taxa, a decrease in species diversity and a remarkable increase in eutrophic taxa. Here, we combined calcareous nannofossil and planktonic foraminifera biostratigraphy from ODP Hole 756C (Ninetyeast Ridge, Indian Ocean), as well as new benthic foraminifera and bulk sediment stable isotope (C, O) records, which documents ocean-climate changes and provides independent chemostratigraphy. Our results provide further support to previous records documenting an invigorated Southern Ocean circulation associated with the transport of cooler and nutrient-enriched waters toward low-middle latitudes.

始新世-渐新世过渡期（Eocene-Oligocene Transition, 简称EOT，约34 Ma）以钙质超微化石（calcareous nannofossil）组合的演化为标志性特征，并与表层海水温度及营养盐供给的变化相耦合。在该过渡期内，钙质超微化石组合发生了突发性更替：喜暖贫营养类群永久衰减，物种多样性下降，而富营养类群则显著增多。本研究整合了大洋钻探计划（Ocean Drilling Program, ODP）756C孔（印度洋九十东洋脊）的钙质超微化石与浮游有孔虫（planktonic foraminifera）生物地层学数据，以及新获取的底栖有孔虫（benthic foraminifera）及全岩沉积物碳、氧稳定同位素（stable isotope）记录，这些数据不仅记录了海洋-气候系统的演化过程，还提供了独立的化学地层学（chemostratigraphy）依据。本研究结果为此前的相关记录提供了进一步支撑：此前研究表明，伴随低温富营养水体向中低纬度的输送，南大洋（Southern Ocean）环流出现增强。