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元素微量金属的浓度和同位素组成。这一点很重要，因为微量金属是光合藻类所必需的，它们在海水中的丰度与大气中CO2的减少和全球气候的调节密切相关。富营养的微量金属通过一系列来源（包括河流）输送到海洋，最终沉积到一些汇中，包括海洋沉积物。对于许多金属来说，海洋沉积物是最重要的汇，而沉积物矿物则是最重要的沉积宿主。特别是铁和锰的氧化物能够从上覆水柱和沉积物孔隙水中吸收金属，并在很长一段时间内锁定金属。随着沉积物被掩埋和俯冲，这些金属最终重新出现在大陆上，并再次风化并通过河流运回海洋。在较短的时间尺度内，铁和锰的氧化物可以老化和转化，新的研究表明，在转化过程中，这些矿物可以释放一些金属库存。此外，铁和锰矿物可在沉积物变为低氧时发生部分溶解，这也可能导致其金属负荷的释放。特别是我们小组的新研究表明，随着氧化锰水钠锰矿的老化和转化，它可以释放高达一半的镍含量（阿特金斯等人，2016年）。镍是海水中重要的微量营养元素，因为它是光合作用所必需的，因此沉积物和海水中的镍含量和同位素组成可能影响和反映现代和古代初级生产力。虽然对于镍来说，水钠锰矿的老化和转化可能会对镍的循环产生巨大影响，但一些重要的问题仍然不清楚：镍是否会随着其他沉积物矿物的老化和转化而释放出来？海洋沉积物矿物部分溶解时是否释放镍？其他微量营养元素微量金属，如钴、铜和锌，是否在海洋沉积物矿物老化和转变以及部分溶解时从其中释放出来？沉积有机物的存在如何影响微量营养元素微量金属的吸收和释放？吸收和释放过程是否会给微量营养素痕量金属提供同位素信号，我们可以用它来跟踪这些重要元素在海洋中的全球循环？在这个项目中，您将调查镍和其他微量元素微量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，使用实验和分析相结合的方法，有机会使用钻石光源同步加速器的最先进的纳米级探针，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.