NOAA/WDS Paleoclimatology - Cariaco Basin oxygenation and circulation over the past 578,000 years

We present results from analyses of the redox-sensitive metals Mo, V, Mn, and Fe in sediment recovered from the Cariaco Basin (Ocean Drilling Program Leg 165, site 1002). Results are interpreted in the context of previous studies of δ15N, export production (percent total organic carbon), eolian input, and hemipelagic deposition in the basin. Variations in redox metal ratios over the past ∼578,000 years were compared to variations in δ18O at Milankovitch frequencies and show a strong relationship between glacial-interglacial cycles in sea level, governed by the shallow sills encircling Cariaco Basin, and bottom water oxygen content. During 100 kyr and 41 kyr cyclicity, enrichments of Mo and V occur during highly productive interglacials, indicating bottom water anoxia. During glacials, sediments are less depleted or enriched in Mn and Fe relative to the interglacials, reflecting oxic conditions. During 23 kyr and 19 kyr cyclicity, however, these redox metal patterns are not observed, indicating that the Cariaco Basin responds differently to the higher-frequency climate changes.

本研究报道了从大洋钻探计划（Ocean Drilling Program）第165航次1002站位获取的卡里亚科盆地（Cariaco Basin）沉积物中，氧化还原敏感金属（redox-sensitive metals）钼（Mo）、钒（V）、锰（Mn）与铁（Fe）的分析结果。本研究结合该盆地此前关于δ15N、输出生产力（export production，即总有机碳占比）、风尘输入（eolian input）与半远洋沉积（hemipelagic deposition）的相关研究，对上述分析结果进行解译。我们将过去约57.8万年以来氧化还原金属比值的变化与米兰科维奇频率（Milankovitch frequencies）下的δ18O变化进行对比，发现受环绕卡里亚科盆地的浅海槛（shallow sills）控制的海平面冰期-间冰期旋回（glacial-interglacial cycles），与底层水含氧量（bottom water oxygen content）之间存在显著关联。在10万年（100 kyr）与4.1万年（41 kyr）的旋回周期中，钼与钒的富集现象出现在生产力极高的间冰期，指示底层水处于缺氧（anoxia）状态。而冰期沉积物中的锰与铁含量相较于间冰期则亏损程度更低，甚至出现富集，这反映了此时底层水处于有氧（oxic conditions）环境。但在2.3万年（23 kyr）与1.9万年（19 kyr）的旋回周期中，并未观测到上述氧化还原金属分布模式，这表明卡里亚科盆地对更高频率的气候变化存在差异化响应。