Stable isotope record of planktonic foraminifera of sediment core TR163-19

Stable isotope data from eastern equatorial Pacific (EEP) core TR163-19 (2°15'N, 90°57'W, 2348 m) are presented for the surface-dwelling foraminifers Globigerinoides ruber and G. sacculifer and thermocline-dwelling Globorotalia menardii and Neogloboquadrina dutertrei. Using species-specific normalization factors derived from experimental and plankton tow data, we reconstruct a 360 kyr record of water column hydrography across the past three glacial cycles. We demonstrate that G. ruber maintains a mixed layer habitat throughout the entire record, while G. sacculifer records a mixture of thermocline and mixed layer conditions and G. menardii and N. dutertrei record thermocline properties. We conclude that G. sacculifer is not appropriate for paleoceanographic applications in regions with steep vertical hydrographic gradients. Results suggest that this region of the EEP had a thicker mixed layer and deeper d13CDIC boundary between the surface and equatorial undercurrent during the last two glacial periods. A shift in N. dutertrei and G. sacculifer geochemistry prior to ~185 kyr suggests water column structure and chemocline gradients changed, possibly due to a shift in the position of the undercurrent relative to this site. The timing and magnitude of glacial-interglacial d13C variations between species indicates that near-surface carbon chemistry is controlled by changes in productivity, atmospheric circulation, and advected intermediate water sources north of the Antarctic polar front. These results demonstrate that when properly calibrated for species differences, multispecies geochemical data sets can be invaluable for reconstructing water column structure and properties in the past.

本研究提供了东赤道太平洋（eastern equatorial Pacific, EEP）TR163-19岩芯（坐标2°15'N，90°57'W，水深2348米）的稳定同位素数据，测试对象包括表层浮游有孔虫：玫瑰拟抱球虫（Globigerinoides ruber）、袋拟抱球虫（Globigerinoides sacculifer），以及温跃层栖息的曼氏厚壁虫（Globorotalia menardii）和杜氏新抱球虫（Neogloboquadrina dutertrei）。研究利用实验及浮游生物拖网数据得到的物种特异性校正因子，重建了过去3个冰期旋回以来长达36万年的水柱水文特征记录。结果显示，玫瑰拟抱球虫在整个记录中始终栖息于表层混合层；袋拟抱球虫的地球化学记录反映了温跃层与混合层的混合环境，而曼氏厚壁虫与杜氏新抱球虫的记录则代表温跃层水体属性。研究据此得出结论：袋拟抱球虫不适用于垂直水文梯度陡峭区域的古海洋学研究。结果表明，在末次两个冰期阶段，东赤道太平洋该站位的表层混合层更厚，表层与赤道潜流之间的溶解无机碳碳同位素（d13CDIC）界面更深。约18.5万年前，杜氏新抱球虫与袋拟抱球虫的地球化学特征发生偏移，指示水柱结构与化学跃层梯度发生变化，这可能源于赤道潜流相对该岩芯站位的位置偏移。不同物种间冰期-间冰期碳同位素变化的时间与幅度显示，近表层水体的碳化学特征受初级生产力变化、大气环流，以及南极极锋以北平流输送的中层水源共同调控。本研究结果证实，若针对物种差异进行恰当校准，多物种地球化学数据集对于重建过去的水柱结构与水体属性具有极高的研究价值。