Stable oxygen isotope record and relative abundances of planktonic foraminifera of ODP Hole 117-728A

High resolution stratigraphy based on oxygen isotope ratios of the planktonic foraminifers Neogloboquadrina dutertrei (d'Orbigny), Globigeriniodes ruber (d'Orbigny), and Globigerina bulloides (d'Orbigny), magnetic susceptibility, and calcium carbonate content covers the sedimentary record of ODP Hole 728A drilled on the Oman Margin from approximately 10 k.y. to 525 k.y., comprising isotopic stages 1-13. Below stage 13 isotopic stage boundaries cannot be defined with certainty in our data. Sediment accumulation rates were calculated from the isotopic record of N. dutertrei by matching it with the age model SPECMAP curve. During the glacial periods sediment accumulation rates were higher than during the interglacial periods, reflecting increased input from the shelf during low-stands of sea level and increased eolian input. Periodograms for the past 524 k.y. on oxygen isotope records of N. dutertrei, G. ruber, and G. bulloides, on calcium carbonate content, magnetic susceptibility, and on a foraminiferal fragmentation record show powers matching the Milankovitch periodicities. High powers are concentrated around 103 k.y. In the spectra of oxygen isotope ratios of N. dutertrei, magnetic susceptibility, and foraminiferal fragmentation these are significant at the 80% confidence level with respect to a first order autoregressive model. Power concentrations near 43 k.y., matching obliquity, are present but subdued in all spectra. Power concentrations near 23 k.y., matching precession, are significant in the spectra of the oxygen isotope record of N. dutertrei, magnetic susceptibility, and calcium carbonate content record. Fragmentation of planktonic foraminifers increased during the interglacial periods. This is attributed to dissolution of the tests in an expanded oxygen minimum zone (OMZ), where undersaturation of calcium carbonate is caused by enhanced production in the euphotic zone, which would suggest stronger monsoonal induced upwelling during interglacial periods. Extension of the OMZ could also be increased by outflow of low oxygen marginal basin bottom water.

基于浮游有孔虫（planktonic foraminifers）杜氏新球虫（Neogloboquadrina dutertrei, d'Orbigny）、红拟抱球虫（Globigeriniodes ruber, d'Orbigny）与泡状抱球虫（Globigerina bulloides, d'Orbigny）的氧同位素比值、磁化率及碳酸钙含量构建的高分辨率地层序列，覆盖了阿曼陆缘大洋钻探计划（Ocean Drilling Program, ODP）728A钻孔距今约10千年至525千年的沉积记录，对应深海氧同位素阶段1至13。在同位素阶段13之下，本研究数据无法明确界定同位素阶段界线。
沉积堆积速率通过杜氏新球虫的同位素记录与SPECMAP曲线年龄模型匹配计算得到。冰期阶段的沉积堆积速率高于间冰期，这反映了海平面低位期陆架输入增强与风尘输入增加。
对过去524千年的多项记录开展周期图分析，包括杜氏新球虫、红拟抱球虫、泡状抱球虫的氧同位素记录，碳酸钙含量、磁化率以及有孔虫破碎率记录，其功率谱峰值与米兰科维奇旋回周期高度吻合。103千年左右的功率峰值最为显著。在杜氏新球虫氧同位素比值、磁化率以及有孔虫破碎率的频谱中，该峰值在一阶自回归模型参照下达到80%置信水平。所有频谱中均存在与斜度周期（约43千年）匹配的功率集中区，但强度较弱。与岁差周期（约23千年）匹配的功率集中区则在杜氏新球虫氧同位素记录、磁化率以及碳酸钙含量记录的频谱中达到显著水平。
浮游有孔虫的破碎率在间冰期阶段升高，这归因于溶解氧最低层（oxygen minimum zone, OMZ）扩张导致的壳体溶解：透光带生产力提升引发碳酸钙不饱和状态，这表明间冰期季风驱动的上升流作用更强。低氧边缘盆地底层水的外流也可能加剧溶解氧最低层的扩张。