Eight ferromanganese crust samples spanning the complete depth range of Tropic Seamount in the northeast Atlantic were analyzed for Pb and Nd isotopes to reconstruct water mass origin and mixing over the last 75 Ma. Pb isotopes were determined by laser ablation multicollector inductively coupled plasma mass spectrometer (LA‐MC‐ICP‐MS), which enables the rapid production of large, high spatial resolution data sets. This makes it possible to precisely correlate stratigraphy between different samples, compare contemporaneous layers, and create a composite record given the abundance of hiatuses in crusts. Pb and Nd isotope data show the influence of various oceanic and continental end‐members in the northeast Atlantic Ocean. This reflects its evolution from a restricted, isolated basins in the Late Cretaceous with influxes from the Tethys Ocean, to an increasingly well‐mixed, large‐scale basin, with a dominant Southern Ocean signature until the Miocene. Less radiogenic Nd isotope signatures suggest Labrador Sea Water influenced the northeast Atlantic basin as early as 17–15 Ma, flowing through a northern route such as the Charlie‐Gibbs Fracture Zone. Pb and Nd isotopes highlight the increasing influence of Saharan eolian dust input about 7 Ma, imparting a less radiogenic excursion to the binary mixing between North Atlantic water masses and riverine discharge from West and Central Africa. This highlights the influence of eolian dust input on the open ocean Pb and Nd budget and supports an early stage of North African aridification in the Late Miocene. This signature is overprinted about 3 Ma to the present by a strong North Atlantic Deep Water signature following the onset of Northern Hemisphere glaciation.

中文翻译：

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利用铅和钕同位素研究相关的铁锰结壳地层及其在大西洋古海洋重建中的应用

分析了横跨东北大西洋热带海山整个深度范围的8个锰铁结壳样品的Pb和Nd同位素，以重建水质量起源并在最后75 Ma内进行混合。铅同位素是通过激光烧蚀多收集器电感耦合等离子体质谱仪（LA-MC-ICP-MS）确定的，从而可以快速生成大型，高空间分辨率的数据集。这样就可以精确地关联不同样本之间的地层，比较同期层，并在地壳中存在大量裂隙的情况下创建复合记录。铅和钕的同位素数据显示了东北大西洋中各种海洋和大陆末端成员的影响。这反映出它是从白垩纪晚期一个受限制的孤立盆地演化而来的，这些盆地来自特提斯海洋，到一个日益混杂的大型盆地，直到中新世为止，它一直是南大洋的主要标志。较少的放射性Nd同位素特征表明，拉布拉多海水早在17-15 Ma时就影响了东北大西洋盆地，流经北部路线，例如Charlie-Gibbs断裂带。Pb和Nd同位素突显了大约7 Ma的撒哈拉风尘输入增加的影响，对北大西洋水体与西非和中非河流排放之间的二元混合影响较小。这突出了风尘输入对公海Pb和Nd预算的影响，并支持中新世晚期北非干旱化的早期阶段。