The availability of dissolved iron (Fe) limits primary production over some regions of the surface ocean, especially in regions such as the subarctic North Pacific. In this work, we use Fe stable isotope ratios (δFe) in bulk and size-fractionated marine aerosol particles and dissolved Fe of surface seawater in the subarctic North Pacific on Japanese GEOTRACES cruise GP02 (Summer 2017) as a tracer to clarify the relative contribution of combustion and natural Fe in both marine aerosol particles and surface seawater. The bulk aerosols collected in the coastal regions of both East Asia and western North Pacific have total δFe values that are as low as −0.5 ‰ when compared to crustal (+0.1 ‰), with both the water-soluble phase and the fine particles even more fractionated (as low as −1.9 and −2.8 ‰, respectively). The negative correlation between the aerosol δFe signatures and the enrichment factors of Fe and other elements dominated by anthropogenic sources (e.g., lead and cadmium) in these coastal regions indicates the presence of Fe emitted from high-temperature combustion sources, such as coal combustion and metal smelting. In these regions, combustion Fe accounts for 4–13 and 13–45 % of the total and water-soluble aerosol Fe, respectively. The results demonstrate that soluble aerosol Fe sourced from combustion Fe can be equivalent to that sourced from natural dust Fe in these coastal regions. By contrast, the aerosol particles in pelagic regions were near crustal δFe in all particle size fractions, indicating the dominance of natural Fe and little to no combustion Fe. The relationships among the fractional Fe solubility, major ion concentration, Fe species, and δFe indicate that the presence of combustion Fe is the dominant reason for the solubility increase in the coastal regions and that the atmospheric processing of mineral dust during transport is more important in the pelagic regions. The dissolved Fe of the surface seawater at 10 m depth had a consistently higher δFe by up to +1.5 ‰ than that of the simultaneously collected water-soluble aerosol Fe. The pattern of the elevated δFe in the surface seawater corresponds to decreasing Fe concentrations and can be approximated by Rayleigh fractionation; we attribute these elevated surface δFe values to the effect of biological uptake. New Fe fluxes from both the atmosphere and deeper depths are limited at least in summer compared with the biological uptake in the open ocean of the subarctic North Pacific.

中文翻译：

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通过稳定铁同位素比追踪供应给亚北极北太平洋的大气铁的来源和归宿


溶解铁 (Fe) 的可用性限制了表层海洋某些区域的初级生产，特别是在亚北极北太平洋等区域。在这项工作中，我们使用日本 GEOTRACES 巡航 GP02（2017 年夏季）上的散装和尺寸分级海洋气溶胶颗粒中的 Fe 稳定同位素比率 (δFe) 以及亚北极北太平洋表层海水中的溶解 Fe 作为示踪剂，以阐明相对贡献海洋气溶胶颗粒和表层海水中的燃烧和天然铁。东亚和西北太平洋沿海地区收集到的散装气溶胶的总 δFe 值与地壳 (+0.1%) 相比低至-0.5%，且水溶性相和细颗粒均均匀更多分馏（分别低至 -1.9 和 -2.8 ‰）。这些沿海地区气溶胶 δFe 特征与 Fe 和其他以人为来源（例如铅和镉）为主的元素的富集因子之间的负相关性表明存在高温燃烧源排放的 Fe，例如煤炭燃烧和金属冶炼。在这些地区，燃烧铁分别占总铁和水溶性气溶胶铁的 4-13% 和 13-45%。结果表明，来自燃烧铁的可溶性气溶胶铁与这些沿海地区来自天然尘埃的铁相当。相比之下，远洋区域的气溶胶颗粒在所有粒径部分都接近地壳 δFe，这表明天然铁占主导地位，燃烧铁很少甚至没有。 Fe 溶解度分数、主要离子浓度、Fe 形态和 δFe 之间的关系表明，燃烧 Fe 的存在是沿海地区溶解度增加的主要原因，并且矿物粉尘在运输过程中的大气处理在沿海地区更为重要。远洋地区。 10 m 深度表层海水中溶解的 Fe 的 δFe 始终比同时收集的水溶性气溶胶 Fe 的高 1.5 ‰。表层海水中 δFe 升高的模式对应于 Fe 浓度的降低，并且可以通过瑞利分馏来近似；我们将这些升高的表面 δFe 值归因于生物吸收的影响。与亚北极北太平洋公海的生物吸收相比，至少在夏季，来自大气和更深深处的新铁通量是有限的。