One of the primary sources of micronutrients to the sea surface in remote ocean regions is the deposition of atmospheric dust. Geographic patterns in biogeochemical processes such as primary production and nitrogen fixation that require micronutrients like iron (Fe) are modulated in part by the spatial distribution of dust supply. Global models of dust deposition rates are poorly calibrated in the open ocean, owing to the difficulty of determining dust fluxes in sparsely sampled regions. We present new estimates of dust and Fe input rates from measurements of dissolved and particulate thorium isotopes ²³⁰Th and ²³²Th on the FS Sonne SO245 section (GEOTRACES process study GPpr09) in the South Pacific. We first discuss high‐resolution upper water column profiles of Th isotopes and the implications for the systematics of dust flux reconstructions from seawater Th measurements. We find dust fluxes in the center of the highly oligotrophic South Pacific Gyre that are the lowest of any mean annual dust input rates measured in the global oceans, but that are 1‐2 orders of magnitude higher than those estimated by global dust models. We also determine dust‐borne Fe fluxes and re‐assess the importance of individual Fe sources to the surface South Pacific Gyre, finding that dust dissolution, not vertical or lateral diffusion, is the primary Fe source. Finally, we combine our estimates of Fe flux in dust with previously‐published cellular and enzymatic quotas to determine theoretical upper limits on annual average nitrogen fixation rates for a given Fe deposition rate.

中文翻译：

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来自钍同位素的南太平洋大气尘埃输入、铁循环和生物地球化学联系

偏远海洋区域海面微量营养素的主要来源之一是大气尘埃的沉积。需要铁 (Fe) 等微量营养素的初级生产和固氮等生物地球化学过程中的地理模式部分受粉尘供应的空间分布的调节。由于难以确定采样稀疏地区的尘埃通量，因此全球尘埃沉积率模型在开阔海洋中校准不佳。我们通过对南太平洋 FS Sonne SO245 部分（GEOTRACES 过程研究 GPpr09）溶解和颗粒钍同位素 ²³⁰Th 和 ²³²Th 的测量，提供了对灰尘和 Fe 输入速率的新估计。我们首先讨论钍同位素的高分辨率上部水柱剖面以及对海水钍测量重建尘埃通量系统学的影响。我们发现在高度贫营养的南太平洋环流中心的尘埃通量是在全球海洋中测量的任何平均年度尘埃输入率中最低的，但比全球尘埃模型估计的高 1-2 个数量级。我们还确定了尘埃携带的 Fe 通量并重新评估了单个 Fe 源对南太平洋环流表面的重要性，发现尘埃溶解，而不是垂直或横向扩散，是主要的 Fe 源。最后，