Interactions of trace metals with dissolved organic matter and colloids in the Amazon and Pará River estuaries and associated plume as key processes for trace metal fluxes into the Atlantic

亚马逊和帕拉河系统向海洋排放的淡水最多，形成了从陆地向海洋输入痕量金属和溶解有机物(DOM)的重要界面。除了亚马逊河对全球海洋痕量金属预算的影响外，其微量营养素的投入对沿海和陆架区域内外的生物生产力也有很大影响。拟议项目的主要目标是了解痕量金属的化学形态和物理化学粒度分馏在亚马逊河和邻近的帕拉河与大西洋的混合连续体中的作用。我们将研究亚马逊和帕拉河河口的水柱和表层沉积物中的痕量金属与DOM和胶体的相互作用，以及相关的羽流，以及帕拉河东南与地下水排放的红树林带。这将有助于更好地了解富含DOM的大型热带河流对海洋痕量金属收支的贡献。基于2018年大流量M147号科考船期间采集的水和沉积物(包括孔隙水)以及我们实验室产生的初步数据，我们将调查更大的亚马逊流出区沿盐度梯度的痕量金属分布和形态的变化。为了评估是什么控制了河口和羽流中痕量金属的化学和物理形态以及迁移，我们将重点研究三个不同的过程：·痕量金属颗粒的分级、吸附和去除：痕量金属在河流颗粒物上的吸附和胶体凝聚的去除，以及粒度分级；痕量金属与不同的可溶性、胶体和颗粒态的结合如何沿盐度梯度变化，这对源-汇平衡意味着什么？·溶液络合：形成可溶的金属-有机络合物；在富含DOM的河口系统中，这一过程如何通过与胶体上的吸附和迁移竞争来加强金属的运输？·沉积物中的痕量金属：沉积物和孔隙水如何充当痕量金属的汇和源，并对该区域的痕量金属通量作出贡献？除了对M147样品进行伏安法和电感耦合等离子体质谱分析外，我们还将通过对即将在亚马逊地区进行邮轮M174期间收集的海水和河水端元进行实验室混合实验，完成对不同元素组(保守的、颗粒反应的和有机络合的)混合行为的系统调查。在此基础上，我们期望获得世界上最大的河口系统中控制痕量金属生物地球化学和元素通量的复杂过程的整体图景。这一知识对于预测由于该地区持续的人为影响和不断变化的气候条件而产生的潜在影响也将是重要的。

The Amazon and Pará River systems discharge the largest volume of freshwater into the ocean and form an important interface for trace metal and dissolved organic matter (DOM) input from land into the ocean. In addition to the impact of the Amazon River on the global ocean trace metal budget, its micronutrient input also has a large influence on the biological productivity within the coastal and shelf region and beyond. The main goal of the proposed project is to understand the role of chemical speciation and physico-chemical size fractionation of trace metals in the mixing continuum of the Amazon River and the neighboring Pará River to the Atlantic Ocean. We will study the interactions of trace metals with DOM and colloids in the water column and surface sediments of the Amazon and Pará estuaries and the associated plume as well as the mangrove belt with groundwater discharge southeast of the Pará River. This will help to better understand the contribution of large DOM-rich tropical rivers to the trace metal budget in the ocean. Based on water and sediment including pore water samples taken during research cruise M147 in the high-discharge period of 2018 and preliminary data produced in our lab, we will investigate changes of trace metal distributions and speciation in the larger Amazon outflow region along the salinity gradients. To assess what controls the chemical and physical speciation and transport of trace metals in the estuary and plume we will focus on three different processes: • Trace metal size fractionation, sorption and removal: sorption of trace metals on riverine particulate matter and removal due to coagulation of colloids, and size fractionation; how do trace metal associations with different soluble, colloidal and particulate fractions change along the salinity gradient, and what does this mean for the source-sink balance?• Solution complexation: formation of soluble metal-organic complexes; how does this process enhance the metal transport by competition with the sorption on colloids and removal in an DOM-rich estuarine system? • Trace metals in sediments: how do sediments and pore water act as a sink and source of trace metals and contribute to the trace metal fluxes in the region? In addition to voltametric and ICP-MS analyses of the M147 samples, we will complete a systematic investigation of the mixing behavior of diverse groups of elements (conservative, particle-reactive and organically-complexed) by conducting laboratory mixing experiments with seawater and river water endmembers collected during the upcoming cruise M174 in the Amazon region. With this, we expect to obtain a holistic picture of the complex processes controlling trace metal biogeochemistry and elemental fluxes in this largest estuarine system of the world. This knowledge will also be important to foresee potential effects in this area due to ongoing anthropogenic impact in this region and changing climatic conditions.