Biogeochemcial Cycling and Authigenic Mineral Formation in Amazon Shelf Sediments

9422470亚马逊河每年向南美洲东部的热带大陆架输送约12亿公吨的泥沙。覆盖着大部分沉积物的无定形铁、锰和铝氧化物的潜在反应层暴露在大陆架上，暴露在海水中，与来自海洋浮游生物的活性有机物混合，然后沉积在陆架沉积物中，在那里它经历了各种成岩(与埋葬有关的)生物地球化学反应。在过去的工作中记录了各种这样的成岩过程后，PI现在将更详细地研究亚马逊陆架矿床中的各种矿物，并试图区分那些来自大陆的矿物与那些通过成岩反应就地形成的矿物。矿物学分析将包括透射电子显微镜、X射线衍射和电子探针，以确定颗粒结构和成分--特别是来自大陆来源的新沉淀矿物，并记录原始沉积颗粒表面涂层的形成和/或溶解。氧、锶和硼同位素分析将有助于确定各种矿物相的来源(大陆或海洋)。这项研究在地球物理上具有挑衅性，主要有两个原因。在古沉积沉积物中发现了一些自生的亚马逊陆架矿物，如菱铁矿(一种还原的碳酸铁)，其古环境特征尚不清楚，长期以来一直存在争议；在今天的沉积物中确定这些矿物的来源可能有助于解决这些问题。其次，亚马逊河是世界海洋淡水、溶质和沉积物的主要贡献者；因此，了解输送到其三角洲的物质的命运对于了解全球海洋地球化学的很大一部分很重要。

9422470 Savin The Amazon River delivers about 1.2 billion metric tons of sediment annually to the eastern tropical continental shelf of South America. The potentially reactive layer of amorphous iron, manganese, and aluminum oxides coating much of this sediment is exposed on the continental shelf to seawater, mixed with labile organic matter derived from marine plankton, and then deposited in shelf sediments where it undergoes a variety of diagenetic (burial-related) biogeochemical reactions. Having documented a variety of such diagenetic processes in their past work, the PIs will now look in more detail at the variety of minerals in Amazon Shelf deposits and attempt to distinguish those of continental origin from those which have been formed in situ by diagenetic reaction. Mineralogical analysis will involve transmission electron microscopy, X-ray diffraction, and electron microprobe to determine particle structures and composition -especially to newly-precipated minerals from those of continental origin and to document the formation and/or dissolution of surface coating over originally deposited particles. Oxygen, strontium, and boron isotope analyses will be used help establish the origin (continental or marine) of the variuos mineral phases. This research is geophysically provocative for two main reason. Some authigenic Amazon Shelf minerals like siderite (a reduced iron carbonate) are found in ancient sedimentary deposits whose paleoenvironmental characteristics are unclear and have long been in dispute; determining the origin of such minerals in present-day deposits could help solve such problems. Secondly, the Amazon River is a major contributor of fresh water, solutes, and sediments to the world ocean; thus understanding the fate of materials delivered to its delta is important for understanding a large part of global marine geochemistry.