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。铁在海水中是如此不溶，以至于从河流进入的大量铁不能被运送到远离大陆边缘的地方。落在海洋上的尘埃提供的铁成为向公海添加铁（以及其他对生命重要的元素，如磷）的主要方式。因此，从大气到海洋表面的铁的模式和通量对海洋生态系统和全球碳循环（因为海洋生物消耗碳）非常重要。尽管如此重要，但对尘埃及其所含金属流入海洋的通量知之甚少。直接测量这种通量具有挑战性，而其他观测方法需要相当基本的假设，这限制了准确性。因此，目前，大多数估计的灰尘通量依赖于大气模型，通常被认为是不确定的因素，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的灰尘及其相关的微量营养素的海洋。这种方法依赖于测量两种生物活性，部分可溶性成分的灰尘：钍（Th）和铝（Al）。Th的两种同位素用于该评估。232Th，存在于大陆岩石中。如果发现232Th溶解在开阔的海洋中，那么它一定是最近由大陆尘埃的溶解而增加的。另一种同位素230 Th是在海水中由铀同位素衰变形成的。其在海水中的浓度反映了这种已知的形成速率与由于其不溶性而被去除的速率之间的竞争。因此，我们可以使用230 Th来评估海水中Th（包括232 Th）的去除率。为了保持观测到的232Th浓度，被去除的232Th必须被尘埃输入所取代，因此我们可以计算尘埃输入。有两个主要的挑战重建尘埃通量Th同位素。一个是Th在尘埃中的溶解度，通量计算中的一个关键术语，是不为人所知的。我们的新研究结果表明，Th是一小部分元素之一，其溶解度几乎不受大气尘埃传输的影响，而Fe，Al和其他几种生物活性元素的溶解度在传输过程中都发生了很大的变化。使用一系列研究巡航中收集的气溶胶样品，并在百慕大的采样塔，我们将评估Th的溶解度，控制如何在大气传输过程中变化，以及它的关系，铝和铁的溶解度的变化。我们还将进行实验室研究，旨在更好地了解不寻常的Th在尘埃气溶胶中的溶解度的沙漠尘埃母土。粉尘通量也可以计算从溶解铝浓度，但这些估计是受大气传输过程中铝溶解度的变化。第二个挑战是，我们不知道232Th在海岸输入后可能会离开大陆多远。我们将通过将232Th纳入海洋模型来解决这个问题。这些模型具有重建230 Th的能力，我们将开发它们来模拟232 Th，并指出232 Th主要由沿海输入而不是由灰尘主导。这些模型也将用于评估使用Th同位素重建尘埃输入的不确定性。最近，在一个国际计划GEOTRACES期间，对海水中Th同位素进行了大量的观测。我们将增加数据从两个进一步的巡航，完成详细的覆盖面的Th和Al测量为Atlantic Ocean.Combined使用的Th和Al示踪剂，因此，将使我们能够产生强大的地图的尘埃输入（从Th）和可溶性铁输入（考虑到在运输过程中使用铝的溶解度的变化）为大西洋（与相关的地图的不确定性）。

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