Understanding the Modern and Past Mercury Biogeochemical Cycle Using Hg Stable Isotopes

使用汞稳定同位素了解现代和过去的汞生物地球化学循环

• 批准号: RGPIN-2018-06569
• 负责人: Bergquist, Bridget
• 金额: $ 2.62万
• 依托单位: University of Toronto
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=645262
• 关键词: Understanding; Modern; Past; Mercury; Biogeochemical

The long-term goal of my research program is to use Hg isotopes to improve our understanding of the Hg biogeochemical cycle and to develop Hg isotopes as a proxy of past environmental changes. Mercury is a globally distributed metal that bioaccumulates in aquatic food webs leading to dangerous exposure in humans and wildlife. Mercury is often emitted to the atmosphere in its reduced form, gaseous elemental Hg (GEM), by both natural and anthropogenic sources. GEM is relatively stable and has a long residence time (~1 yr), which allows it to be distributed globally. Eventually GEM is oxidized and deposited to terrestrial and aquatic systems quickly (hours to weeks). One of the major complexities of the Hg cycle is that after deposition, Hg can be reduced back to GEM and emitted back to the atmosphere. This results in primary sources making up less than half of the Hg emissions to the atmosphere (30% anthropogenic, 10% natural) with 60% of inputs to the atmosphere being Hg re-emissions dominantly from soils and the ocean. Many key knowledge gaps still hinder our understanding of both the modern and past Hg cycle and make it challenging to predict how changes in emissions and climate will affect the Hg cycle. For example, assessing the relative contributions of different anthropogenic sources versus re-emissions on local, regional and global scales is a huge challenge and is often dependent on models without enough constraints from data. Also, a recent assessment of GEM exchange to and from soils highlighted that very large uncertainties still exist especially in forested ecosystems. ****** A rapidly growing tool to study Hg is Hg stable isotope geochemistry, which was largely driven by the discovery of large mass independent fractionation (MIF) of Hg isotopes. My Discovery program will focus on three goals that are exciting new areas where Hg isotopes are likely to make large impacts on the field of Hg research: (1) the development and application of new methods to measure Hg concentrations and isotopic compositions of atmospheric Hg species, (2) the use of Hg isotopes to quantify and understand sources and remobilization of Hg in soils, and (3) the development and testing of Hg and Hg isotopes as a proxy of ancient volcanic emissions. Objectives 1 and 2 will advance modelling and assessment of sources of Hg to the atmosphere and to soils through much needed experimental studies, novel development of samplers for collection and isotopic analysis of Hg, and fieldwork to verify and apply new techniques. The third objective will investigate a primary natural source of Hg to the atmosphere, volcanism, and the isotopic signatures of volcanic Hg species along with how these signatures are preserved in geological records. The isotopic characterization of this geogenic source of Hg will contribute to our understanding of the modern Hg cycle and will establish the baseline for Hg isotopes as a reliable tracer of ancient volcanic emissions.

我的研究计划的长期目标是使用汞同位素来提高我们对汞地球化学循环的理解，并开发汞同位素作为过去环境变化的代理。汞是一种全球分布的金属，在水生食物网中生物积累，导致人类和野生动物危险的接触。汞通常以还原态气态元素汞（GEM）的形式通过自然和人为来源排放到大气中。吉西他滨相对稳定，滞留时间长（约1年），可在全球范围内销售。最终，GEM被氧化并迅速沉积到陆地和水生系统中（数小时至数周）。汞循环的主要复杂性之一是，汞在沉积后可还原为GEM并排放回大气。这导致主要来源的汞排放量不到大气汞排放量的一半（30%人为排放，10%自然排放），而大气汞排放量的60%主要来自土壤和海洋。许多关键的知识差距仍然阻碍着我们对现代和过去汞循环的理解，并使预测排放和气候变化将如何影响汞循环变得困难。例如，在地方、区域和全球范围内评估不同人为源与再排放的相对贡献是一项巨大的挑战，而且往往依赖于没有足够数据约束的模型。此外，最近对GEM与土壤之间的交换进行的一项评估突出表明，仍然存在很大的不确定性，特别是在森林生态系统中。****** 汞稳定同位素地球化学是研究汞的一个快速发展的工具，这在很大程度上是由汞同位素的大质量独立分馏（MIF）的发现所推动的。我的发现计划将侧重于三个目标，这些目标是令人兴奋的新领域，汞同位素可能会对汞研究领域产生重大影响：（1）开发和应用新方法测量大气中汞的浓度和同位素组成，（2）利用汞同位素定量和了解土壤中汞的来源和再活化，（3）开发和测试汞和汞同位素作为古火山排放的替代物。目标1和目标2将通过急需的实验研究、开发新的汞收集和同位素分析采样器，以及开展实地工作以验证和应用新技术，推进大气和土壤中汞来源的建模和评估。第三个目标是调查大气中汞的主要自然来源、火山活动、火山汞物种的同位素特征沿着以及这些特征如何保存在地质记录中。这一地质来源的汞的同位素表征将有助于我们了解现代汞循环，并将建立汞同位素作为古火山排放的可靠示踪剂的基线。