Seafloor nutrient factories: The use of silicon and germanium isotopes to investigate early marine sediment diagenesis

浅层沉积物通过溶解和其他化学反应释放的元素是海洋系统中关键营养物质的重要来源，这些营养物质对支持生物生产和碳循环至关重要。溶解的硅（Si）就是这样一种营养物质，它对硅藻的生长至关重要，硅藻是一种重要的藻类，在海洋中产生的有机碳中占很大比例。浅层沉积物含有各种硅反应池，是各种海洋环境下上覆水域溶解硅的重要来源（例如Michalopolous & Aller， 2004），特别是在缺乏大量河流硅输入的地区。锗（Ge）是硅的“化学孪生体”，其稳定同位素可与硅同位素一起用于研究这些先前未开发的活性二氧化硅池，这些活性二氧化硅池与大陆边缘和陆架海中的非生物和氧化还原敏感氧化物和氢氧化物以及生物二氧化硅有关（Baronas等人，2019；Guillermic等人，2017；Ng等人，2019；Pokrovsky等人，2014）。项目目标和方法总体目标是使用配对的硅和锗同位素来研究大陆架浅层沉积物中的活动过程，以更好地了解沉积物中溶解的Si向上覆水域的释放，并更好地约束海洋Ge预算。具体目标将包括使用布里斯托尔同位素组的尖端等离子体质谱法，对海水、孔隙水和沉积物浸出分析进行改进Ge同位素测量；在受控的实验室实验中，与DISL的Jeffrey Krause合作对反应样品中的Ge同位素进行分析；分析来自高纬度和低纬度大陆架海洋的天然沉积物样品中的Si和Ge同位素以及无机常量营养素和微量金属（例如铁和锰）。该项目具有灵活性，可以专注于Ge/Si分析方法开发的特定方面，更广泛的氧化还原敏感同位素系统（例如，在卡迪夫大学测量的铀同位素）的实验室或现场分析，或地球化学建模。

The release of elements from shallow sediments through dissolution and other chemical reactions is an important source of key nutrients into the marine system that are essential for supporting biological production and carbon cycling. Dissolved silicon (Si) is one such nutrient, which is critical for the growth of diatoms, an important group of algae that are responsible for a significant proportion of organic carbon production in the oceans. Shallow sediments contain various reactive pools of silica and are an important source of dissolved silicon to overlying waters in various marine settings (e.g. Michalopolous & Aller, 2004), especially in areas lacking significant fluvial silicon input. Germanium (Ge) is the 'chemical twin' of Si, and its stable isotopes could be used together with Si isotopes to investigate these previously under-explored reactive silica pools, associated with non-biological and redox-sensitive oxides and hydroxides, as well as biological silica within continental margins and shelf-seas (Baronas et al., 2019; Guillermic et al., 2017; Ng et al., 2019; Pokrovsky et al., 2014).Project Aims and MethodsThe overall aim is to use paired silicon and germanium isotopes to investigate active processes within shallow sediments from continental shelves, to better understand the release of dissolved Si from sediments into overlying waters, and to better constrain the marine Ge budget. The specific objectives will include refining Ge isotope measurements for seawater, porewater, and sediment leach analyses using cutting-edge plasma mass spectrometry methods within the Bristol Isotope Group; analysis of Ge isotopes within samples reacted under controlled laboratory experiments carried out in collaboration with Jeffrey Krause at DISL; analysis of Si and Ge isotopes as well as inorganic macronutrients, and trace metals (e.g. iron and manganese) in natural sediment samples from contrasting high and low-latitude continental shelf seas. There is flexibility within the project to focus on specific aspects of Ge/Si analytical method development, laboratory or field analyses of a wider range of redox-sensitive isotope systems (e.g uranium isotopes, measured at Cardiff University), or geochemical modelling.