(Table 3) Stable oxagen isotope record of planktonic foraminifera from Central Walvish Ridge

Above the Walvis Ridge, in the SE Atlantic Ocean, we collected living plantkic foraminifera from the upper water column using depth stratified plantkon tows. The oxygen isotope composition (d18Oc) in shells of foraminifera and shell concentration profiles show seasonal and depth habitats of individual species. The tow results are compared with the average annual deposition d18Oc from sediment traps and the interannual average d18Oc of fossil specimens in top sediments at the same site. The species Globigerinita glutinata best reflects the austral winter/spring sea surface temperature (SST). Its d18Oc signal in top sediments remains pristine. In contrast, tow results also show that Globigerinoides ruber continues to calcify below the surface mixed layer (SML), i.e., down to the deep chlorophyll maximum (DCM); hence its d18Oc signature of exported specimens reflects the SST only when SML incorporates the DCM. Deep tow and sediment trap results show that both Globorotalia truncatulinoides and Globorotalia inflata record the temperature between 150 and 350 m, depending on the season and the shell size. However, for all fossil taxa in sediments apart from Globigerinita glutinata, we observe a positive d18Oc shift with respect to the sediment trap and plankton tow values, likely related to the interannual flux changes and deep encrustation.

本研究于东南大西洋沃尔维斯海岭（Walvis Ridge）上方海域，采用分层浮游拖网（depth-stratified plankton tows）采集上层水体中的活体浮游有孔虫（planktonic foraminifera）。通过分析有孔虫壳体的氧同位素组成（d18Oc）与壳体浓度剖面，可揭示各物种栖息的季节与深度分布特征。将拖网采样结果与同一站位沉积物捕集器（sediment traps）的年平均沉积d18Oc信号，以及表层沉积物中化石标本的年平均d18Oc信号进行对比。
其中胶粘球室虫（Globigerinita glutinata）的壳体同位素信号最能反映南半球冬、春季的海表温度（SST），且其在表层沉积物中的d18Oc信号保持原始状态。与之相反，拖网结果显示红拟抱球虫（Globigerinoides ruber）可在表层混合层（SML）下方直至深层叶绿素最大值层（DCM）的范围内进行钙化作用；因此其输出壳体的d18Oc信号仅当表层混合层覆盖深层叶绿素最大值层时，才能反映海表温度。
深层拖网与沉积物捕集器结果表明，截圆抱球虫（Globorotalia truncatulinoides）与膨抱球虫（Globorotalia inflata）的壳体同位素信号所记录的水深介于150~350 m之间，具体数值随季节与壳体尺寸而异。但除胶粘球室虫外，沉积物中所有其他化石类群的d18Oc值均较沉积物捕集器与浮游拖网的观测值偏高，这一现象大概率与年际通量变化及壳体深层结壳作用相关。