(Table AT1) Grain size distribution and stable isotope record of benthic foraminifera of ODP Hole 175-1085A

The Walvis Paradox states that opal accumulation fluctuates in counterphase to general productivity on Walvis Ridge, off northern Namibia. Sediments of early Quaternary age from Site 1085 (Cores 175-1085A-7H to 10H, off South Africa) were studied to check the phase relationships of general productivity and opal deposition in the region off the Oranje River, near the southern end of the Namibia upwelling system. The proxies used are delta18O of Cibicidoides wuellerstorfi, delta13C of C. wuellerstorfi, benthic foraminifers per gram (BF/g), Uvigerina spp. per gram (U/g), estimated diatom abundance (EDA) and sulfide and oxide aggregates (SOA) in the coarse fraction. EDA and BF/g are taken to indicate diatom and organic matter productivity, respectively. Oxygen isotopes were used to determine phase within the glacial-interglacial cycles.
The phase relationships between the different proxies emerge when applying internal stacking methods. For Core 175-1085A-7H, five prescribed 41-k.y. cycles were combined into an average 41-k.y. cycle for the different indices. Productivity indices (BF/g and U/g) tend to follow delta18O in the accustomed manner (with glacial periods showing maximum productivity), but not EDA, whose maximum appears closer to interglacials, offset toward cooling. Thus, phase relationships are similar to those on Walvis Ridge, extending the Walvis Paradox to the southern end of the Namibia upwelling system for the early Quaternary. A tentative reconstruction of the phase of intensity of mixing is given, based on the two productivity indicators EDA and BF/g. Mixing is strongest during the glacial maximum.

沃尔维斯悖论（Walvis Paradox）指出，纳米比亚北部外海的沃尔维斯海岭（Walvis Ridge）上，蛋白石堆积量与区域总生产力呈反相波动。为验证奥兰治河（Oranje River）外、纳米比亚上升流系统（Namibia upwelling system）南端附近海域的总生产力与蛋白石沉积的相位关系，研究人员对南非外海1085站位（Site 1085）的早更新世沉积物开展了研究，所用岩心为175-1085A-7H至10H（Cores 175-1085A-7H to 10H）。本次研究采用的代用指标（proxies）包括：乌陵斯福迪圆辐虫（Cibicidoides wuellerstorfi）的δ¹⁸O（delta18O）、乌陵斯福迪圆辐虫的δ¹³C（delta13C）、每克底栖有孔虫数量（benthic foraminifers per gram，BF/g）、每克卷转虫属（Uvigerina）物种数量（Uvigerina spp. per gram，U/g）、估算硅藻丰度（estimated diatom abundance，EDA）以及粗组分（coarse fraction）中的硫化物与氧化物集合体（sulfide and oxide aggregates，SOA）。其中EDA与BF/g分别用以表征硅藻生产力与有机质生产力。研究人员通过氧同位素（oxygen isotopes）分析确定冰期-间冰期旋回（glacial-interglacial cycles）内的相位。采用内部堆叠法（internal stacking methods）可揭示不同代用指标间的相位关系。针对岩心175-1085A-7H，研究人员将5个预设的41千年旋回（41-k.y. cycles）整合为各指标的平均41千年旋回序列。结果显示，生产力代用指标（productivity indices）BF/g与U/g遵循常规模式，与δ¹⁸O变化同步（冰期（glacial periods）时生产力达峰值），但EDA并不遵循该模式：EDA的峰值更接近间冰期（interglacials），且向冷却期偏移。因此，该海域的相位关系与沃尔维斯海岭的特征一致，将沃尔维斯悖论的适用范围扩展至早更新世的纳米比亚上升流系统南端。最后，研究基于EDA与BF/g这两个生产力指标，对混合强度的相位进行了初步重建，结果表明冰盛期（glacial maximum）时混合作用最强。