Ocean Dust Deposition Rates Constrained in a Data‐Assimilation Model of the Marine Aluminum Cycle
Ocean Dust Deposition Rates Constrained in a Data‐Assimilation Model of the Marine Aluminum Cycle
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DOI：
10.1029/2021gb007049
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发表时间：
2021-08
影响因子：
5.2
通讯作者：
Hairong Xu;T. Weber
中科院分区：
文献类型：
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作者：
Hairong Xu;T. Weber
铝(Al)通过风尘被输送到表层海洋水域，使其成为一种有希望的示踪剂，用于限制粉尘沉积速率和大气中痕量金属微量营养素的供应。近年来，沿GeOTRACES横断面绘制了溶解Al的地图，提供了无与伦比的世界海洋覆盖范围。然而，从这些观测数据推断大气输入速率是复杂的，因为有一系列影响铝分布的额外过程，包括可逆的颗粒清除、硅藻的生物吸收、热液来源、沉积物再悬浮。在这里，我们使用了一个海洋铝循环的数据同化模型，该模型明确地解释了这些过程，允许提取大气信号。我们进行了一系列模型优化，测试了不同的尘埃沉积分布，并考虑了铝溶解度的空间变化，从而推断出与GEOTRACES观测最一致的大气铝供应。我们发现，37.2±11.0GmoL/年的可溶Al被添加到全球海洋中，主要分布在大西洋，并且Al的分数溶解度随大气沙尘浓度的变化而强烈变化。我们的模型还表明，6.1±2.4GmoL Al/yr是从热液喷口注入的，铝在水柱中的垂直再分配主要是非生物的可逆清除作用，而不是硅藻的吸收。我们的结果对海洋铁(Fe)的收支有重要的意义：根据沙尘中可溶Fe/Al的比值，我们推断全球风成Fe输入在3.82-9.25Gmol/年之间，不能满足大多数海洋地区的生物Fe需求。
Aluminum (Al) is delivered to surface ocean waters by aeolian dust, making it a promising tracer to constrain dust deposition rates and the atmospheric supply of trace metal micronutrients. Over recent years, dissolved Al has been mapped along the GEOTRACES transects, providing unparalleled coverage of the world ocean. However, inferring atmospheric input rates from these observations is complicated by a suite of additional processes that influence the Al distribution, including reversible particle scavenging, biological uptake by diatoms, hydrothermal sources, sediment resuspension. Here we employ a data‐assimilation model of the oceanic Al cycle that explicitly accounts for these processes, allowing the atmospheric signal to be extracted. We conduct an ensemble of model optimizations that test different dust deposition distributions and consider spatial variations in Al solubility, thereby inferring the atmospheric Al supply that is most consistent with GEOTRACES observations. We find that 37.2 ± 11.0 Gmol/yr of soluble Al is added to the global ocean, dominated in the Atlantic Ocean, and that Al fractional solubility varies strongly as a function of atmospheric dust concentration. Our model also suggests that 6.1 ± 2.4 Gmol Al/yr is injected from hydrothermal vents, and that vertical Al redistribution through the water column is dominated by abiotic reversible scavenging rather than uptake by diatoms. Our results have important implications for the oceanic iron (Fe) budget: based on the soluble Fe:Al ratio of dust, we infer that aeolian Fe inputs lie between 3.82 and 9.25 Gmol/yr globally, and fall short of the biological Fe demand in most ocean regions.