Abstract Hydrogenetic ferromanganese crusts are considered a faithful record of the isotopic composition of seawater influenced by weathering processes of continental masses. Given their ubiquitous presence in all oceans of the planet at depths of 400–7000 meters, they form one of the most well-distributed and accessible records of water-mass mixing and climate. However, their slow accumulation rate and poor age constraints have to date limited their use to explore 100 ka paleoclimatic phenomena. Here it is shown how the Pb isotope signature and major element content of a Fe-Mn crust from the north-east Atlantic responded to changes in the intensity and geographic extent of monsoonal rainfall over West Africa, as controlled by climatic precession during the Paleocene. The studied high-spatial resolution (4 μm) laser-ablation multi-collector inductively coupled plasma mass spectrometer (LA-MC-ICP-MS) Pb isotope data is a nearly 2 order of magnitude improvement in spatial and temporal resolution compared to micro-drill subsamples. The record demonstrates cyclicity of the 206Pb/204Pb and 208, 207Pb/206Pb ratios at the scale of single Fe-Mn oxide laminae, in conjunction with variations in the Fe/Mn ratio, Al, Si and Ti content. Time-frequency analysis and astronomical tuning of the Pb isotope data demonstrates the imprint of climatic precession (∼20 ka) modulated by eccentricity (∼100 and 405 ka), yielding growth rates of 1.5–3.5 mm/Ma consistent with previous chemostratigraphic age models. In this context, boreal summer at the perihelion causes stronger insolation over West Africa, resulting in more intense and geographically extended monsoonal rainfalls compared to aphelion boreal summer conditions. This, in turn, influences the balance between the weathering endmembers feeding the north-east Atlantic basin. These results provide a new approach for calibrating Fe-Mn crust records to astronomical solutions, and allow their isotopic and chemical archive to be exploited with an improved temporal resolution of 1000–5000 years.

中文翻译：

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大西洋铁锰结壳中米兰科维奇旋回的地球化学证据

摘要 水成因铁锰结壳被认为是受大陆物质风化过程影响的海水同位素组成的忠实记录。鉴于它们在地球所有海洋中 400-7000 米深处无处不在，它们构成了水团混合和气候分布最广、最易获取的记录之一。然而，迄今为止，它们缓慢的积累速度和较差的年龄限制限制了它们用于探索 100 ka 古气候现象。此处显示了来自东北大西洋的 Fe-Mn 地壳的 Pb 同位素特征和主要元素含量如何响应西非季风降雨强度和地理范围的变化，这是由古新世期间的气候岁差控制的。研究的高空间分辨率 (4 μm) 激光烧蚀多接收器电感耦合等离子体质谱仪 (LA-MC-ICP-MS) Pb 同位素数据与微米级相比在空间和时间分辨率上提高了近 2 个数量级。钻取子样本。该记录证明了 206Pb/204Pb 和 208、207Pb/206Pb 比率在单个 Fe-Mn 氧化物层级的循环性，以及 Fe/Mn 比率、Al、Si 和 Ti 含量的变化。对 Pb 同位素数据的时频分析和天文调谐表明，气候进动（~20 ka）受偏心率（~100 和 405 ka）调节的印记，产生 1.5-3.5 mm/Ma 的增长率，与以前的化学地层年龄模型一致. 在这种情况下，近日点的北方夏季对西非造成更强的日照，与远日点北方夏季条件相比，导致更强烈和地理范围更广的季风降雨。这反过来又会影响供给大西洋东北部盆地的风化端元之间的平衡。这些结果提供了一种将 Fe-Mn 地壳记录校准为天文解的新方法，并允许利用它们的同位素和化学档案，以提高 1000-5000 年的时间分辨率。