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Using Uranium Series Radiogenic Isotopes to Trace and Quantify Chemical Fluxes in the Atlantic Ocean

使用铀系列放射性同位素追踪和量化大西洋中的化学通量

基本信息

批准号：
1941565
负责人：
金额：
--
依托单位：
University of Oxford
依托单位国家：
英国
项目类别：
Studentship
财政年份：
2017
资助国家：
英国
起止时间：
2017 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=studentship-1941565
关键词：
Using Uranium Series Radiogenic Isotopes

项目摘要

Currently the magnitude of hydrothermal trace-element flux to the oceans is poorly constrained for a number of reasons. Firstly, we have only discovered a small number of the total hydrothermal vents in our oceans and the majority of these sites are relatively large, well-established, focussed vent sites such as TAG (Trans-Atlantic Geo-traverse), Rainbow or Lost City along the Mid-Atlantic Ridge. Even at sites such as TAG, which have been studied extensively, the timescale of the loss or transformation of elements such as iron via chemical, biological or particle scavenging is poorly constrained.Radio-isotopes provide a tool to understand the timescale of such processes. Radium (Ra) is present in the ocean as four naturally occurring radioactive isotopes: 223Ra, 224Ra, 226Ra and 228Ra, with half-lives (11.4 d, 3.66 d, 1600 y and 5.75 y, respectively) and acts conservatively in the water column. Understanding vertical or horizontal fluxes within the neutrally buoyant plume could be achieved using Ra-isotope ratios. Normalising a short-lived isotope against a long-lived one corrects for any Ra scavenging or dilution. Hence if the neutrally buoyant plume is sampled at a given distance and the end-member isotope-ratio is known the sample can be aged using the change in sample activity. This would provide a timescale that could be related to changes in trace-element concentrations between the end-member and sample-site (Kipp et al. 2017).Oceanic radium activities are incredibly low; therefore large sample volumes are required. Such samples could be obtained via the use of Stand Alone Pumping Systems (SAPS) in conjunction with polymer-fibre filter cartridges, impregnated with manganese oxide. The water would be pumped through the filter cartridge and the manganese oxides on the fibres would strip radium from the water as it passes through, concentrating the radium on the cartridge (Moore et al., 1973). The activity of this cartridge could then be determined using a Radium Delayed-Coincidence Counter (RaDeCC) (Moore et al., 1996).In reality, there are multiple vents that run the length of a margin such as the Mid-Atlantic Ridge as well as physical processes that cause the mixing of vent fluids. However, the timescales provided by radium-isotope measurements would be a powerful tool in improving the hydrothermal trace-element flux estimates produced by current models.

目前，由于若干原因，热液微量元素流入海洋的数量很少受到限制。首先，我们在海洋中只发现了一小部分热液喷口，其中大多数喷口都是相对较大的、已确立的、集中的喷口，如TAG（跨大西洋地理穿越）、Rainbow或沿着大西洋中脊的迷城。即使在TAG这样的地点，已经被广泛研究，铁等元素通过化学、生物或颗粒清除而损失或转化的时间尺度也很难限制。放射性同位素提供了一种工具来了解这种过程的时间尺度。镭（Ra）在海洋中以四种天然存在的放射性同位素存在：223 Ra、224 Ra、226 Ra和228 Ra，半衰期分别为11.4天、3.66天、1600 y和5.75 y，在水柱中的作用是保守的。了解垂直或水平通量内的中性浮力羽可以实现使用Ra同位素比。将短寿命同位素相对于长寿命同位素进行归一化，可以校正任何Ra清除或稀释。因此，如果在给定距离处对中性浮力羽流进行采样，并且端元同位素比已知，则可以使用样品活性的变化对样品进行老化。这将提供一个时间尺度，可能与端元和样品位置之间的痕量元素浓度变化有关（Kipp等人。2017）。海洋镭活动非常低;因此需要大量样品。这些样本可以通过使用独立泵送系统（SAPS）与聚合物纤维过滤筒结合使用，浸渍氧化锰。水将被泵送通过滤筒，并且纤维上的锰氧化物将在水通过时从水中剥离镭，将镭集中在滤筒上（摩尔等人，1973年）。然后可以使用镭延迟符合计数器（Radium Delayed-Coincidence Counter，RaDeCC）（摩尔等人，实际上，在大西洋中脊等边缘上有多个喷口，还有造成喷口流体混合的物理过程。然而，镭同位素测量所提供的时间尺度将是一个强有力的工具，可以改进现有模型所产生的热液微量元素通量估计。