Atmospheric fluxes of mineral dust-derived soluble trace elements to the ocean using thorium isotopes (ThorMap)

使用钍同位素计算源自矿物尘埃的可溶性微量元素进入海洋的大气通量 (ThorMap)

• 批准号: NE/V001213/1
• 负责人: Alexander Baker
• 金额: $ 74.39万
• 依托单位: University of East Anglia
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FV001213%2F1
• 关键词: Atmospheric; fluxes; mineral; dust; derived

Biological productivity (the growth of phytoplankton) is limited by the availability of iron (Fe) in at least 30% of the ocean. Fe is so insoluble in seawater that the large amounts entering from rivers cannot be transported far from the continental margins. The supply of Fe from dust falling on the ocean becomes the primary way to add Fe (and other elements important to life such as phosphorus) to the open ocean. The pattern and flux of Fe from the atmosphere to the surface ocean is therefore important for ocean ecosystems, and for the global carbon cycle (because ocean life consumes carbon). Despite this importance, the flux of dust and of its incorporated metals to the ocean is poorly known. It is challenging to measure this flux directly, and other observational approaches require quite fundamental assumptions, which limit accuracy. At present, therefore, most estimates of dust flux rely on atmospheric models, and are generally considered to be uncertain by a factor of ten, particularly in remote regions.In the proposed work, we will assess and use a new approach to quantify the inputs of dust and its associated micronutrients to the ocean. This approach relies on measurements of two biologically inactive, partially soluble components of dust: thorium (Th) and aluminium (Al). Two isotopes of Th are used in this assessment. 232Th, is present in continental rocks. If found dissolved in the open ocean, 232Th must have been recently added by dissolution of dust transported from the continents. Another isotope, 230Th, is formed within seawater by the decay of a uranium isotope. Its concentration in seawater reflects a competition between this known rate of formation, and removal due to its insoluble nature. We can therefore use 230Th to assess the removal rate of Th, including 232Th, from seawater. The 232Th removed must be replaced by input from dust to maintain the observed 232Th concentrations, so we can calculate the input of dust. There are two main challenges to the reconstruction of dust fluxes from Th isotopes. One is that the solubility of Th in dust, a critical term in the flux calculation, is not well known. Our new results indicate that Th is amongst a small group of elements whose solubility is very little impacted by transport of dust through the atmosphere, while the solubilities of Fe, Al and several other biologically active elements are all altered greatly during transport.Using aerosol samples collected on a series of research cruises, and at a sampling tower on Bermuda, we will assess the solubility of Th, the controls on how that varies during atmospheric transport, and its relationship to changes in Al and Fe solubility. We will also conduct laboratory studies on desert dust parent soils aimed at better understanding the unusual Th solubility in dust aerosols. Dust fluxes can also be calculated from dissolved Al concentrations, but these estimates are affected by changes in Al solubility during atmospheric transport. The second challenge is that we do not know how far 232Th from the continents might travel after input at the coast. We will address this by incorporating 232Th into an ocean model. Such models have a proven ability to reconstruct 230Th, and we will develop them to also model 232Th, and to indicate where 232Th is dominated by coastal inputs rather than by dust. These models will also be used to assess the uncertainty in using Th isotopes to reconstruct dust inputs.A large number of observations of Th isotopes in seawater has recently been measured during an international programme: GEOTRACES. We will add data from two further cruises, to complete a detailed coverage of Th and Al measurements for the Atlantic Ocean.Combined use of the Th and Al tracers will therefore allow us to produce robust maps of dust inputs (from Th) and soluble Fe inputs (by taking account of the changes in solubility during transport using Al) for the Atlantic (with associated maps of uncertainty).

生物生产力（浮游植物的生长）受到至少 30% 海洋中铁 (Fe) 可用性的限制。铁很难溶于海水，因此从河流进入的大量铁无法输送到远离大陆边缘的地方。来自海洋上的尘埃提供的铁成为向开放海洋添加铁（以及对生命重要的其他元素，例如磷）的主要方式。因此，铁从大气到表层海洋的模式和通量对于海洋生态系统和全球碳循环非常重要（因为海洋生物消耗碳）。尽管如此重要，但人们对灰尘及其所含金属进入海洋的通量却知之甚少。直接测量这种通量具有挑战性，而其他观测方法需要非常基本的假设，这限制了准确性。因此，目前大多数尘埃通量的估计依赖于大气模型，并且通常被认为不确定性十倍，特别是在偏远地区。在拟议的工作中，我们将评估和使用一种新的方法来量化输入灰尘及其相关微量营养素进入海洋。该方法依赖于对灰尘中两种非生物活性、部分可溶成分的测量：钍 (Th) 和铝 (Al)。本次评估使用了两种钍同位素。 232Th存在于大陆岩石中。如果发现 232Th 溶解在公海中，则一定是最近通过从大陆输送来的尘埃溶解而添加的。另一种同位素 230Th 是通过铀同位素的衰变在海水中形成的。它在海水中的浓度反映了已知的形成速率和由于其不溶性而被去除之间的竞争。因此，我们可以使用 230Th 来评估海水中 Th（包括 232Th）的去除率。去除的 232Th 必须由灰尘的输入代替，以维持观测到的 232Th 浓度，因此我们可以计算灰尘的输入。从Th同位素重建尘埃通量面临两个主要挑战。一是 Th 在灰尘中的溶解度（通量计算中的一个关键术语）尚不清楚。我们的新结果表明，Th 是一小群元素之一，其溶解度几乎不受大气中灰尘运输的影响，而 Fe、Al 和其他几种生物活性元素的溶解度在运输过程中都发生了很大变化。使用气溶胶样品通过一系列研究巡航和百慕大的采样塔收集的数据，我们将评估 Th 的溶解度、其在大气传输过程中变化的控制及其与 Al 和 Fe 溶解度变化的关系。我们还将对沙漠沙尘母土进行实验室研究，旨在更好地了解沙尘气溶胶中异常的钍溶解度。粉尘通量也可以根据溶解的铝浓度来计算，但这些估计值受到大气传输过程中铝溶解度变化的影响。第二个挑战是我们不知道 232Th 在海岸输入后可能会从大陆行驶多远。我们将通过将 232Th 纳入海洋模型来解决这个问题。这些模型已被证明能够重建 230Th，我们将开发它们来模拟 232Th，并表明 232Th 的主要成分是沿海输入而不是灰尘。这些模型还将用于评估使用Th同位素重建灰尘输入的不确定性。最近在一个国际计划GEOTRACES期间测量了海水中Th同位素的大量观测结果。我们将添加另外两次航行的数据，以完成对大西洋 Th 和 Al 测量的详细覆盖。因此，结合使用 Th 和 Al 示踪剂将使我们能够生成灰尘输入（来自 Th）和可溶性 Fe 的可靠地图大西洋的输入（通过考虑使用铝运输过程中溶解度的变化）（以及相关的不确定性地图）。

项目成果

Response of coccolithophore communities to oceanographic and atmospheric processes across the North- and Equatorial Atlantic

• DOI: 10.3389/fmars.2023.1119488
• 发表时间: 2023-04
• 作者: C. Guerreiro;Afonso Ferreira;L. Cros;J. Stuut;A. Baker;Andreia Tracana;Catarina Pinto;V. Veloso;Andrew P. Rees;M. Cachão;Telmo Nunes;V. Brotas