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

对硅酸盐风化过程中碳消耗的估计可能有高达80%的误差，因为他们假设阳离子在溶解和运输过程中的行为是保守的。一组化学反应被称为阳离子交换反应。当带电的矿物表面和水之间形成化学平衡时，它们迅速发生。具有带电表面的最重要的矿物群之一是粘土。这些快速反应在土壤和含水层中得到了很好的研究，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，它就会显著改变自然水体的化学成分和通过化学风化消耗的碳总量，对气候反馈产生重大影响。这个项目将确定粘土矿物和河水之间阳离子交换对化学风化通量的估计的影响，从而对在长时间尺度上缓和气候的反馈的影响。主要目标将通过实验室实验研究的结合，以及对主要河流的水化学和悬浮荷载深度剖面的成对测量来实现，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，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大小。这将通过两种方式完成，首先是一组受控实验，其次是在北极圈内麦肯齐河的实地设置。作为专门探险的一部分，学生将在麦肯齐河河口的盐度梯度处取样成对的悬浮沉积物和水。我们将使用一套同位素比率示踪剂，如Mg、Li和Sr同位素比率来追踪阳离子交换的影响。

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.