Molybdenum (Mo) is an essential trace metal that plays a central role in biological nitrogen fixation (BNF) as the cofactor in the conventional form of the nitrogenase enzyme. The low availability of Mo in soils often constrains BNF in many terrestrial ecosystems. Atmospheric sources may supply a critical source of exogenous Mo to regions with highly weathered soils likely low in Mo, particularly in tropical forests where BNF is thought to be high. Here, we present results of a global model of Mo deposition that considers the principal natural sources of atmospheric Mo—windborne mineral dust, sea-salt aerosols, and volcanic sources—which operate over geologic time. The largest source of mineral dust globally is from North Africa. We quantified Mo concentrations in dust and sediments from the Bodélé Depression, a large source within North Africa, to constrain our model. Because the Mo concentration of seawater is relatively high for a trace element, we also hypothesized that sea-salt aerosols would contribute atmospheric Mo. Our model predicts higher Mo deposition to terrestrial ecosystems along coasts downstream in trade winds, near active volcanoes, and in areas that receive dust deposition from North Africa, such as the northern Amazon Basin, the Caribbean, and Central America. Regions with higher Mo deposition tend to be areas where BNF has previously been measured. The lowest Mo deposition occurs in the high latitudes, northern parts of North America, Western Australia, Southern Africa, and much of central South America. Atmospheric transport of Mo likely plays an important role in supplying Mo to ecosystems across geologic time, particularly in regions with highly weathered soils.

中文翻译：

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钼的自然大气沉积：全球模型及其对热带森林的影响

钼 (Mo) 是一种必需的微量金属，在生物固氮 (BNF) 中作为传统形式固氮酶的辅助因子，在生物固氮 (BNF) 中发挥核心作用。土壤中钼的低可用性通常限制了许多陆地生态系统中的 BNF。大气源可能为高度风化土壤的 Mo 含量可能较低的地区提供重要的外源 Mo，特别是在 BNF 被认为较高的热带森林中。在这里，我们展示了一个全球钼沉积模型的结果，该模型考虑了大气中钼的主要天然来源——风载矿物尘、海盐气溶胶和火山源——它们在地质时期内运行。全球最大的矿物粉尘来源来自北非。我们量化了 Bodélé 洼地的灰尘和沉积物中的钼浓度，这是北非的一个重要来源，来约束我们的模型。由于海水中微量元素的钼浓度相对较高，我们还假设海盐气溶胶会贡献大气中的钼。我们的模型预测，在信风下游、活火山附近和地区，沿海岸的陆地生态系统会有更高的钼沉积接收来自北非的灰尘沉积，例如亚马逊盆地北部、加勒比海和中美洲。Mo 沉积量较高的区域往往是先前测量过 BNF 的区域。最低的钼沉积发生在高纬度地区、北美洲北部、西澳大利亚、南部非洲和南美洲中部的大部分地区。Mo 的大气传输可能在整个地质时期为生态系统提供 Mo 方面发挥重要作用，特别是在土壤高度风化的地区。