Slowly accumulating pelagic clays are enriched in metals that were formerly in seawater, including iron, an important micronutrient. Because the metals are minimally remobilized in oxygenated porewater, pelagic clays may be a potential archive for records of past marine micronutrient cycling. Here, we present a record of changes in hydrogenous iron (Fe) isotopes since the late Cretaceous derived from pelagic clays that we dated with osmium isotope chronostratigraphy. To optimize the separation of the hydrogenous metal (oxy)hydroxides from bulk sediment, we repeatedly leached an oxic pelagic clay sample under variable conditions (HCl molarity, temperature, time) and measured the element concentrations, Fe isotopes, and Os isotopes. The common behavior of elements amidst the permutations of the leach experiment offers insight into which components were dissolved and we defined a range of successful leaches. We applied our optimal leach for Fe and Os isotopes (1 M HCl, for 24 h at 20 °C) to 45 samples at Site U1366 in the South Pacific Gyre. The resulting record suggests a dynamic Fe cycle in the water column overlying Site U1366 over the past 95 million years. Early in the site's history, trends in the Fe isotopes are interpreted as reflecting changes in hydrothermal Fe with distance from the ridge. Contributions from a background Fe source are identified as well as a transition to dust-like source after 50 Ma until present. Constructing similar records at multiple sites will provide a basin-wide perspective on how the marine Fe cycle has changed over million-year timescales.

缓慢堆积的浮游粘土富含以前在海水中的金属，包括铁（一种重要的微量营养素）。由于金属在氧化孔隙水中的迁移最少，因此浮游粘土可能是过去海洋微量营养素循环记录的潜在档案。在这里，我们提供了自白垩纪晚期从远古白垩纪衍生出的含氢铁（Fe）同位素变化的记录，我们通过with同位素年代地层学对此年代进行了研究。为了优化从大量沉积物中分离含氢金属（氧）氢氧化物的方法，我们在可变条件下（HCl摩尔浓度，温度，时间）反复浸出了氧化性上层粘土样品，并测量了元素浓度​​，Fe同位素和Os同位素。在浸出实验的排列中元素的共同行为提供了对哪些成分被溶解的洞察力，并且我们定义了一系列成功的浸出。我们对Fe和Os同位素（1 M HCl，在20°C下持续24 h）应用最佳浸出法，对南太平洋回转中心的U1366站点上的45个样品进行了浸出。结果记录表明，在过去的9500万年中，U1366站点上空的水柱中有一个动态的铁循环。在该站点的历史的早期，铁同位素的趋势被解释为反映了热液中的铁随着距山脊的距离而发生的变化。确定了来自背景铁源的贡献以及从50 Ma到目前的向粉尘状源的过渡。