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: $ 5.25万
• 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: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=751221
• 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利用汞同位素来提高我们对汞生物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，可在水生食物网中生物富集，导致人类和野生动物接触危险。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。 GEM相对稳定，停留时间较长（约1年），使其能够在全球范围内流通。最终 GEM 被氧化并快速（数小时至数周）沉积到陆地和水生系统中。汞循环的主要复杂性之一是沉积后，汞可以还原回 GEM 并排放回大气中。这导致主要来源占大气汞排放量的不到一半（30% 人为，10% 自然），大气排放量的 60% 是主要来自土壤和海洋的汞再排放。许多关键的知识差距仍然阻碍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具有挑战性。例如，评估地方、区域和全球范围内不同人为来源与再排放的相对贡献是一项巨大的挑战，并且通常依赖于没有足够数据约束的模型。此外，最近对与土壤之间的 GEM 交换的评估强调，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增长的工具，这在很大程度上是由汞同位素大质量独立分馏 (MIF) 的发现推动的。我的发现计划将重点关注汞同位素可能对汞研究领域产生重大影响的令人兴奋的新领域的三个目标：（1）开发和应用新方法来测量汞浓度和大气汞物种的同位素组成，(2) 使用汞同位素来量化和了解土壤中汞的来源和再活化，以及 (3) 开发和测试汞和汞同位素作为古代火山的代理排放。目标 1 和 2 将通过急需的实验研究、用于汞收集和同位素分析的采样器的新开发以及验证和应用新技术的现场工作，推进对大气和土壤中汞来源的建模和评估。第三个目标将调查大气中汞的主要自然来源、火山活动和火山汞物种的同位素特征，以及这些特征如何保存在地质记录中。这种汞地质来源的同位素特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代火山排放的可靠示踪剂的基线。