Carbonate and terrigenous content and chemical composition of sediments in the Central Equatorial Pacific

This study addresses changes in the absolute magnitude and spatial geometry of particle flux and export production in a meridional transect across the central equatorial Pacific Ocean's upwelling system during oxygen isotope Stage 11 and Stage 12 and compares these time periods to the current Holocene interglacial system. Temporal and spatial variability in several chemical proxies of export production, and in particular the distributions of Ba, scavenged Al, and P, are studied in a suite of sediment cores gathered along a cross-equator transect at 5°S, 2°S, 0°, 2°N, and 4°N. Because this latitudinal range preserves strong gradients in biogenic particle flux in the modern equatorial Pacific Ocean, we are able to assess variations in the relative magnitude of export production as well as the meridional width of the equatorial system through the late Quaternary glacial/interglacial cycles. During interglacial oxygen isotope Stage 11 the chemical proxies each indicate lower particle flux and export production than during Stage 12. These records are consistent throughout the transect during this time period, but geographic narrowing (during the interglacial) and widening (during the glacial) of the meridional gradient also occurs. Although carbonate concentration varies dramatically through glacial/interglacial cycles at all latitudes studied, the productivity proxies record only minimal glacial/interglacial change at 5°S and 4°N, indicating that the carbonate minima at these latitudes is controlled dominantly by dissolution rather than production. The chemical data indicate that although the spatial geometry of the system during Stages 11 and 12 indicates maximum productivity at the equator during both glacial and interglacial conditions, the absolute magnitude of export production integrated from 5°S to 4°N during Stage 11 was 25-50% less than during Stage 12, and also was 25-50% less than it is now.本研究聚焦氧同位素11期（Stage 11）与12期（Stage 12）期间，赤道中太平洋上升流系统经向断面上颗粒通量与输出生产力的绝对量级及空间结构变化，并将这两个时期与现代全新世（Holocene）间冰期系统开展对比。本研究以沿5°S、2°S、0°、2°N及4°N跨赤道断面采集的系列沉积岩芯为对象，系统分析输出生产力的多种化学代用指标（chemical proxies，尤其是钡（Ba）、吸附态铝（scavenged Al）及磷（P）的分布特征）的时空变化规律。鉴于该纬度区间在现代赤道太平洋中存在显著的生源颗粒通量（biogenic particle flux）梯度，本研究得以评估晚第四纪（late Quaternary）冰期-间冰期旋回（glacial/interglacial cycles）中输出生产力的相对量级变化，以及赤道系统的经向宽度演化。在间冰期氧同位素11期，各化学代用指标均显示颗粒通量与输出生产力低于12期。该时期整个断面上的记录均保持一致，但经向梯度也呈现出间冰期阶段收缩、冰期阶段扩张的地理分布特征。尽管所有研究纬度的碳酸盐浓度（carbonate concentration）均随冰期-间冰期旋回发生显著波动，但在5°S与4°N站位，生产力代用指标仅记录到极微弱的冰期-间冰期变化，表明这些纬度的碳酸盐浓度低值主要受控于溶解作用（dissolution）而非生源碳酸盐生产。化学数据显示，尽管11期与12期的系统空间结构均表明，无论冰期还是间冰期，赤道区域的生产力均达到峰值，但5°S至4°N范围内的总输出生产力绝对量级在11期较12期降低25%~50%，同时也较现代低25%~50%。