Muddying the waters: cation exchange processes as a major control on weathering fluxes.

搅浑水：阳离子交换过程是风化通量的主要控制因素。

• 批准号: 2393952
• 金额: --
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2393952
• 关键词: Muddying; waters; cation; exchange; processes

Estimates of carbon consumption by silicate weathering could be wrong by up to 80% because they assume that cations behave in a conservative way during dissolution and transport. One suite of chemical reactions are referred to as cation exchange reactions. They occur rapidly as a chemical equilibrium develops between charged mineral surfaces and a water. One of the most important mineral groups which have charged surfaces are clays. These rapid reactions are well studied in soils and aquifers, but the scientific community working on river chemistry has largely neglected these reactions. Our work shows that once the cation exchange process is taken into account it changes significantly the chemistry of natural waters and the total amount of carbon consumption through chemical weathering, with major implications for climate feedbacks.This project will determine the impact of cation exchange between clay minerals and river waters on estimates of chemical weathering fluxes and thus on the feedback which moderates climate on long timescales. The main objective will be achieved by a combination of laboratory experimental studies, and paired measurements of water chemistries and suspended load depth-profiles on major rivers allowing re-evaluation of silicate chemical weathering fluxes. The student will determine the magnitude of the release of cations from the suspended load exchange pool when rivers enter the ocean and Na replaces Ca, Mg and Sr on exchange sites. This will be done in two ways, firstly with a set of controlled experiments, and secondly in the field setting of the Mackenzie River in the Arctic Circle. The student will sample paired suspended sediment and water across the salinity gradient in the estuary of the Mackenzie River as part of a dedicated expedition. We will trace the effects of cation exchange using a suite of isotope ratio tracers such as Mg, Li and Sr isotope ratios.

对硅酸盐风化造成的碳消耗的估计可能错误高达 80%，因为他们假设阳离子在溶解和运输过程中表现得保守。一组化学反应称为阳离子交换反应。当带电矿物表面和水之间形成化学平衡时，它们会迅速发生。具有带电表面的最重要的矿物组之一是粘土。这些快速反应在土壤和含水层中得到了充分研究，但研究河流化学的科学界在很大程度上忽视了这些反应。我们的工作表明，一旦考虑到阳离子交换过程，它就会显着改变天然水体的化学性质以及化学风化产生的碳消耗总量，对气候反馈产生重大影响。该项目将确定粘土之间阳离子交换的影响矿物和河水对化学风化通量的估计，从而对长期尺度上调节气候的反馈进行了研究。主要目标将通过实验室实验研究以及主要河流的水化学和悬浮负荷深度剖面的配对测量来实现，从而重新评估硅酸盐化学风化通量。学生将确定当河流进入海洋且 Na 取代交换点上的 Ca、Mg 和 Sr 时，悬浮负载交换池中阳离子释放的程度。这将通过两种方式完成，首先是一组受控实验，其次是在北极圈麦肯齐河的实地环境中。作为专门探险的一部分，学生将在麦肯齐河口的盐度梯度上对悬浮沉积物和水进行采样。我们将使用一套同位素比示踪剂（例如镁、锂和锶同位素比）来追踪阳离子交换的影响。