Abstract To test the biological effectiveness of iron fertilization by Asian aeolian dust and volcanic ash in the stratified high-nitrate, low-chlorophyll subarctic Pacific Ocean over long-time scales, we analysed sediments with ages between 2.8 and 0.9 Ma at ODP Site 885/886. This site lies far from the influence of other iron sources (e.g. icebergs or lateral iron transportation) and the water column has been stratified since intensification of northern hemisphere glaciation (iNHG) at ∼2.7 Ma, which limits nutrient upwelling and makes it an ideal location for testing iron bioavailability of different atmospheric sources that fell onto the surface ocean. We investigate diatom assemblages and opal export changes, and compare them with the properties of iron minerals in Asian aeolian dust and volcanic ash. Our results reveal that Asian aeolian dust contains mostly unreactive iron-bearing minerals that supplied limited bioavailable iron for diatom growth at Site 885/886. Diatom productivity changes were dominated by upwelling/stratification changes over long timescales, and by sporadic iron fertilization from volcanic ash inputs. Iron from volcanic ash particles is likely to have become bioavailable because such particles dissolved more readily due to their high porosity and ultra-fine size.

中文翻译：

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层状高硝酸盐低叶绿素亚北极太平洋风尘和火山灰中铁肥的相对重要性测试

摘要 为了测试亚洲风尘和火山灰在分层高硝酸盐、低叶绿素亚北极太平洋地区长期尺度上的铁肥化作用，我们分析了 ODP Site 885/ 年龄在 2.8 到 0.9 Ma 之间的沉积物。 886. 该地点远离其他铁源（如冰山或横向铁运输）的影响，自北半球冰川作用（iNHG）在~2.7 Ma加剧以来，水柱已分层，这限制了养分上涌，使其成为理想的地点用于测试落在海洋表面的不同大气来源的铁生物有效性。我们调查了硅藻组合和蛋白石出口变化，并将它们与亚洲风尘和火山灰中铁矿物的特性进行了比较。我们的结果表明，亚洲风成尘主要包含非反应性含铁矿物质，这些矿物质为 Site 885/886 的硅藻生长提供了有限的生物可利用铁。硅藻生产力的变化主要由长时间尺度上的上升流/分层变化以及来自火山灰输入的零星铁肥所主导。火山灰颗粒中的铁很可能已成为生物可利用的，因为此类颗粒由于其高孔隙率和超细尺寸而更容易溶解。