Bioavailability and biogeochemical cycling of iron in glacially-influenced fjord systems of the high Arctic, Spitsbergen (Svalbard)

冰川来源的铁是大陆架水域潜在生物可利用铁的重要来源，但在很大程度上不受限制。这种微量营养素可在沿海上升区，特别是大型北冰洋大陆架的初级生产力的肥沃过程中发挥重要作用。更广泛地说，冰川来源的铁可能在冰期-间冰期时间尺度上的全球铁循环中发挥重要和动态的作用，并在面对气候变化时发挥作用。该项目的目标是三个北极峡湾(斯皮茨卑尔根和斯瓦尔巴群岛)铁的生物地球化学循环，重点是生物可利用铁的来源和跨峡湾系统的转移及其在峡湾沉积物中的成岩氧化还原循环。具体地说，我们计划检验这样的假设：(1)冰川融水排放和冰川径流带产生的冰川面粉含有大量可生物利用的铁成分，这些铁成分来自冰川下冰川碎屑的生物地球化学风化；(2)这些铁相进入峡湾使水柱中的初级生产力肥沃，并支持邻近峡湾沉积物中异化铁的快速还原；(3)铁的海底循环包括多次溶解和再氧化步骤，有助于活性铁相越过峡湾的嘴并最终到达大陆架。为了实现我们的目标，我们将结合经典的(生物)地球化学分析，特别是孔隙水微量金属测量和顺序铁提取方案，与新开发的抗坏血酸提取方法相结合，该方法专门针对亚铁水合物，从而允许确定生物可利用铁的含量，并分析铁的同位素特征。

Glacially derived iron is an important, yet largely unconstrained source of potentially bioavailable iron to continental shelf waters. This micronutrient may play an important role in the fertilization of primary productivity in coastal upwelling areas particularly on the large Arctic shelf. More generally, glacially derived iron may be a vital and dynamic player in the global iron cycle over glacial-interglacial timescales and in the face of climate change. This project targets the biogeochemical cycling of iron in three Arctic fjords (Spitsbergen, Svalbard) with a focus on the sources and transfer of bioavailable iron across fjord systems and its diagenetic redox cycling in fjord sediments. Specifically, we plan to test the hypothesis that (1) glacial flour from glacial meltwater discharge and proglacial runoff zones contains a large bioavailable iron component deriving from subglacial biogeochemical weathering of glacial debris; (2) the input of these iron phases to the fjords fertilizes primary productivity in the water column and supports high rates of dissimilatory iron reduction in adjacent fjord sediments; and (3) the benthic cycling of iron, encompassing multiple dissolution and re-oxidation steps, facilitates the transport of reactive iron phases across the fjords to their mouths and ultimately to the shelf. To fulfill our objectives we will combine classical (bio)geochemical analyses, particularly pore-water trace metal measurements and sequential iron extraction schemes, with a newly developed ascorbic acid extraction method which specifically targets ferrihydrite and thus allows for the determination of the bioavailable iron content, and the analysis of iron isotope signatures.