Arsenic in gases from shallow-water hydrothermal systems

与深海热液系统相反，海洋浅水热液系统发生在浅水近岸环境中，通过排放通常含有砷（As）的还原热液流体，对沿海海洋产生相当大的影响。流体的排放通常伴随着热液气体的大量排放。目前还不知道这些气体中的砷浓度，虽然砷在热液系统中分配到气相中，并且已知存在于可比的陆基火山气体中，为什么没有在MSWHS中测量到气相中的砷是未知的，尽管可能是收集足够的样品体积和运输到合适的实验室是一种阻碍。从海底热液喷口收集10至25升的气体并非易事，运输这样的体积将是一个问题，考虑到这一点，拟议项目的目标将是开发和测试一种程序，用于捕获和测量MSWHS气相中的挥发性砷。该方法将基于一种既定的方法，即将水下气体收集到最初为汞开发的气密Tedlar®袋中。在收集之后，砷将通过捕集到硅树脂上或NaOCl溶液中从气体中提取。首先，将在实验室条件下测试和优化捕集方法。第二，他们将被应用和测试，在现场采样热液气体从MSWHS在古乔里湾在米洛斯，希腊的南侧。在那里，热液中浓度的升高导致每年有1.5 × 10^4千克砷从海湾流入地中海。然而，挥发性砷部分的估计值仍然缺失，假设浓度与陆基热液系统相似，通过气相的砷通量将为4.5 × 10^4 kg，是通过水相的估计通量的三倍。因此，在Paleochori湾的现场测试应提供足够的砷浓度在气相中，并提供第一个数据，这个砷丰富的MSWHS。一旦成功应用，新开发的方法将提供一个合适的现场程序，从MSWHS全球气体中的砷采样。

Marine shallow-water hydrothermal systems (MSWHS), as opposed to deep-sea hydrothermal systems, occur in shallow-water nearshore settings where they can have a considerable impact on the coastal ocean through discharge of reduced, hot hydrothermal fluids that often contain arsenic (As). The emission of fluids is generally accompanied by the extensive discharge of hydrothermal gases. Nothing is known about the arsenic concentrations in those gases, although arsenic partitions into the gas phase in hydrothermal systems and is known to be present in comparable land-based volcanic gases.Why arsenic has not been measured in the gas phase in MSWHS is unknown, although it is likely that the collection of sufficient sample volume and the transport to a suitable laboratory were a deterrent. To collect anywhere from 10 to 25 L of gas from hydrothermal vents on the seafloor is not trivial, and shipping such volumes would be problematic.With this in mind, the objective of the proposed project will be to develop and test a procedure for trapping and measuring volatile arsenic in the gas phase in MSWHS. The method will be based on an established method of underwater gas collection into gastight Tedlar® bags initially developed for mercury (Hg). Following collection, arsenic will be extracted from the gas by either trapping onto a silicon resin or into a NaOCl solution. First, the trapping methods will be tested and optimized under laboratory conditions. Second, they will be applied and tested in the field by sampling hydrothermal gases from the MSWHS in Paleochori Bay on the south side of Milos, Greece. There, elevated concentrations in the hydrothermal fluids lead to an annual flux of 1.5 × 10^4 kg arsenic from the Bay into the Mediterranean Sea. Still, this estimation is missing for the volatile arsenic fraction and assuming concentrations similar to land-based hydrothermal systems, the arsenic flux via the gas phase would be 4.5 × 10^4 kg, three times the estimated flux via the water phase. Thus, a field test in Paleochori Bay should provide sufficient arsenic concentrations in the gas phase and provide first data for this arsenic-rich MSWHS. Once successfully applied, the newly developed method will provide a suitable field procedure for sampling arsenic in gases from MSWHS worldwide.