Marine Micronutrient Cycling between Sediments and Seawater: What controls the concentration and isotopic composition of micronutrient trace metals in

在这个项目中，您将使用新的和令人兴奋的实验和分析方法来研究海洋沉积物如何帮助控制海水中微量营养素的浓度和同位素组成。这一点很重要，因为光合作用的藻类需要微量金属，而海水中微量金属的丰度与大气二氧化碳的减少和全球气候的调节密切相关。微量金属通过包括河流在内的一系列来源输送到海洋，并最终沉积到包括海洋沉积物在内的许多汇中。对于许多金属来说，海洋沉积物提供了最重要的汇，沉积物矿物提供了最重要的沉积宿主。特别是，铁和锰氧化物能够从上覆水柱和沉积物孔隙水中清除金属，并在很长一段时间内锁定金属。随着沉积物被埋藏和俯冲，这些金属最终重新浮出大陆，并再次风化，被河流输送回海洋。在较短的时间内，铁和锰氧化物会老化和转化，新的研究表明，在转化过程中，这些矿物可以释放出一些金属库存。此外，随着沉积物变得亚氧，铁和锰矿物可能会发生部分溶解，这也可能导致它们的金属负荷释放。特别是，我们小组的新研究表明，随着氧化锰水钠石的老化和变形，它可以释放出多达一半的镍含量(Atkins等人，2016年)。镍是海水中一种重要的微量营养素，因为它是光合作用所必需的，因此沉积物和海水中的镍浓度和同位素组成可能影响和反映现代和古代的初级生产力。虽然对镍来说，水钠长石的老化和转化可能会对镍的循环产生重大影响，但一些重要的问题仍然不清楚：其他沉积物矿物在老化和转化时是否会释放镍？海洋沉积物矿物是否会在部分溶解时释放镍？其他微量营养素金属，如钴、铜和锌，是否会在老化和转化过程中从海洋沉积物矿物中释放出来？并经历部分溶解？沉积有机质的存在如何影响微量营养素痕量金属的吸收和释放？吸收和释放过程是否向微量营养素痕量金属传递同位素信号，我们可以用来跟踪海洋中这些重要元素的全球循环？在这个项目中，您将使用实验和分析相结合的方法，研究镍和其他微量营养素金属在铁和锰氧化物的老化、转化和部分还原溶解过程中的行为，并有机会使用钻石光源同步加速器最先进的纳米级探测器，以及苏黎世ETH同位素地球化学和宇宙化学组的稳定同位素设施。

In this project you will use new and exciting experimental and analytical approaches to investigate how marine sediments help control the concentration and isotopic composition of micronutrient trace metals in seawater. This is important because trace metals are required by photosynthetic algae, and their abundance in seawater is intimately linked to the drawdown of atmospheric CO2 and the regulation of global climate.Micronutrient trace metals are delivered to the oceans via a range of sources, including rivers, and end up being deposited into a number of sinks, including marine sediments. For many metals, marine sediments provide the most important sink, and sediment minerals provide the most important sedimentary hosts. In particular iron and manganese oxides are able to scavenge metals from the overlying water column and from sediment pore-waters and lock up metals over long timescales. As the sediments are buried and subducted, these metals eventually resurface on the continents and are once again weathered and transported back to the oceans by rivers. Over shorter timescales iron and manganese oxides can age and transform, and new research shows that during transformation these minerals can release some of their metal inventory. Moreover iron and manganese minerals can undergo partial dissolution as sediments become sub-oxic, which may also lead to a release of their metal load. In particular new research from our group shows that as the manganese oxide birnessite ages and transforms it can release up to half of its nickel content (Atkins et al., 2016). Nickel is an important micronutrient in seawater because it is required for photosynthesis and thus nickel concentrations and isotopic compositions in sediments and seawater might both influence and reflect modern and ancient primary productivity. While it is clear for nickel that the aging and transformation of birnessite might have a drastic impact on nickel cycling, a number of important questions are still unclear:Is nickel released from other sediment minerals as they age and transform?Is nickel released from marine sediment minerals as they partially dissolve?Are other micronutrient trace metals like cobalt, copper and zinc released from marine sediment minerals as they age and transform, and undergo partial dissolution?How does the presence of sedimentary organic matter affect the uptake and release of micronutrient trace metals?Does the uptake and release process impart an isotopic signal to micronutrient trace metals that we can use to track the global cycling of these important elements in the oceans?In this project you will investigate the behaviour of nickel and other micronutrient trace metals during the aging, transformation and partial reductive dissolution of iron and manganese oxides, using a combined experimental and analytical approach, with the opportunity to use state-of-the-art nanoscale probes at Diamond Light Source synchrotron, and stable isotope facilities in the Isotope Geochemistry and Cosmochemistry Group at ETH Zurich.