Controls on iron and sulfate reduction in Arctic fjord sediments under climate change

该项目的主要目标是了解在海洋沉积物中如何控制有机碳厌氧氧化的两个最重要的过程，即微生物还原铁和硫酸盐。有机质的微生物矿化是海洋沉积物中许多元素循环的驱动力。主要的终端氧化剂不仅影响沉积物的地球化学性质，还影响营养物质的释放，如铁、锰或磷酸盐。末端接受电子的过程随着沉积物中深度的变化而变化，遵循顺序，这被认为是由热力学决定的。然而，铁还原和硫酸盐还原之间的大量空间重叠经常被发现。似乎铁还原微生物和硫酸盐还原微生物之间的竞争受到许多其他因素的影响，比如电子供体的可用性或铁的结晶度，这些因素在动力学上限制了铁还原。然而，目前还不清楚这些不同的因素究竟如何影响海洋沉积物中铁和硫酸盐还原之间的平衡。我将调查在受到气候变化强烈影响的北极海床上，铁还原和硫酸盐还原之间的竞争是如何受到控制的。北冰洋持续的和预计的变暖将改变铁的可获得性，因为冰川径流的增加，以及有机碳的可获得性，这是由于海冰覆盖的减少，从而导致藻类生产力和沉淀物的增加。目前尚不清楚这些变化将如何影响北极沉积物中铁和硫酸盐还原之间的平衡，从而影响生物地球化学。斯瓦尔巴群岛西海岸的峡湾受到气候变化的严重影响，为温暖的大西洋海水与寒冷的北极海水相遇提供了理想的野外场地。在不同峡湾的沉积物中，可以发现不同的地球化学条件，包括有利于铁或硫酸盐还原的条件。我将结合对铁或有机碳含量高或低的沉积物进行的地球化学、微生物学和分子生物学分析，以及对这些沉积物进行精心设计的实验以及纯培养实验。这项研究将缓解北极沉积物对改变的沉积流入反应的敏感度。奥胡斯大学地球微生物学中心是完美的东道主，因为他们在海洋沉积物中的生物地球化学过程和微生物群落方面拥有丰富的专业知识，而且他们在北极的实地工作经验和参与程度也很高。我已经为这个项目进行的初步工作表明，铁和硫酸盐还原之间的平衡对铁和有机碳含量的变化是多么敏感，以及我如何才能进一步推进这项研究。

The primary objective of this project is to understand how the two most important processes for anaerobic oxidation of organic carbon are controlled in marine sediments, namely the microbial reduction of iron and of sulfate. Microbial mineralization of organic matter is a driving force behind many element cycles in marine sediments. The dominant terminal oxidant affects not only the geochemistry of the sediment but also the release of nutrients, such as iron, manganese, or phosphate. The terminal electron-accepting processes change with depth in the sediment, following a sequential order, which is thought to be determined by thermodynamics. Yet, a substantial spatial overlap between iron and sulfate reduction is frequently found. It appears that the competition between iron- and sulfate-reducing microorganisms is affected by many other factors, like the availability of the electron donor or the crystallinity of the iron, what kinetically constrains iron reduction. However, it is not understood how exactly these different factors influence the balance between iron and sulfate reduction in marine sediments.I will investigate how the competition between iron- and sulfate- reducers is controlled in the arctic seabed, which is strongly affected by climate change. The ongoing and predicted warming of the Arctic Ocean will change the availability of iron, due to enhanced glacial runoff, and of organic carbon, due to reduced sea ice cover, what leads to increased algal productivity and sedimentation. It is not understood how these changes will influence the balance between iron and sulfate reduction and consequently the biogeochemistry in Arctic sediments. The fjords on the west coast of Svalbard, which are severely impacted by climate change, provide ideal field sites where warm Atlantic water meets cold Arctic water. In the sediments of the different fjords contrasting geochemical conditions can be found, including conditions favoring either iron or sulfate reduction. I will combine geochemical, microbiological and molecular biological analyses of sediments that have high or low loading of iron or organic carbon with carefully conceived experiments with these sediments as well as pure culture experiments. The study will relieve how sensitively Arctic sediments will respond to altered depositional influx. The Center for Geomicrobiology at Aarhus University is the perfect host because of their great expertise in biogeochemical processes and microbial communities in marine sediments and their experience and engagement in field work in the Arctic. The preliminary work that I already performed for this project showed how sensitive the balance between iron and sulfate reduction is to changed iron and organic carbon content and how I can further progress with this study.