Pliocene-Pleistocene carbon isotope record of foraminifera from DSDP Site 89-586

Oceanographic changes in the western equatorial Pacific during the past 6 m.y. are inferred from carbon isotopic analyses of planktonic and benthic foraminifers from Ontong Java Plateau (DSDP Site 586). Sample spacing is 1.5 m (ca. 35,000-75,000 yr). An overall trend of d13C toward lighter values is evident for the last 5 m.y. in all four foraminiferal taxa analyzed (G. sacculifer, Pulleniatina, P. wuellerstorfi, and O. umbonatus). This trend is interpreted as an enrichment of the global ocean with 12C, because of the addition of carbon from organic carbon reservoirs (or lack of removal of carbon to such reservoirs), as a consequence of an overall drop in sea level. Differences between shallow- and deep-water d13C decrease slightly during this time interval, suggesting a moderate drop in productivity. This drop is not sufficient to explain the drop in sedimentation rate, however, much of which apparently must be ascribed to winnowing effects. A marked convergence in the d13C values of planktonic taxa exists within the last 2 m.y. We propose that this convergence indicates nutrient depletion in thermocline waters, caused by the vigorous removal of phosphate in marginal upwelling regions, or by the stripping of intermediate waters in their source regions. No large shifts are seen in the carbon isotope record of the last 6 m.y., in contrast to the oxygen isotope record. Some indication of cyclicity is present, with a period between 0.5 and 1.0 m.y. (especially in the earlier portion of the record).本数据集基于翁通爪哇海台（Ontong Java Plateau）深海钻探计划（Deep Sea Drilling Project, DSDP）586站位的浮游有孔虫与底栖有孔虫碳同位素分析结果，反演了过去6百万年西赤道太平洋的海洋学变化。样品采样间距为1.5米，对应年代跨度约35000至75000年。对所分析的4种有孔虫类群——囊球拟抱球虫（G. sacculifer）、圆辐虫属（Pulleniatina）、伍氏圆辐虫（P. wuellerstorfi）以及凸背拟单栏虫（O. umbonatus）——的研究显示，过去5百万年其δ¹³C整体呈现向轻值偏移的趋势。该趋势被归因于全球海洋中¹²C的富集，其驱动机制为海平面整体下降引发的有机碳储库碳输入增强（或向此类储库的碳移除减弱）。此期间浅水（浮游生境）与深水（底栖生境）的δ¹³C差值略有减小，指示海洋生产力出现适度下降。然而该下降幅度不足以解释沉积速率的降低，多数沉积速率下降显然应归因于沉积物淘洗作用。 在过去2百万年中，浮游有孔虫类群的δ¹³C值出现显著趋同。我们认为该趋同现象指示温跃层水体出现营养盐耗竭，其成因可能是边缘上升流区对磷酸盐的强烈移除，或是源区中层水被剥离。与氧同位素记录不同，过去6百万年的碳同位素记录未出现显著偏移。记录中存在一定的周期性特征，周期介于0.5至1.0百万年之间（尤其在记录的早期阶段更为显著）。