Mechanisms and effects of benthic biogeochemical iron cycling in glaciated fjords

冰川，沿着河流，热液喷口和风尘，已知是铁的重要来源，铁是一种重要的，但往往限制元素的生活在海洋中。然而，高达95%的冰川铁沉淀到靠近冰源的峡湾沉积物中.目前还不清楚冰川铁的命运是什么，一旦它被出口到峡湾沉积物，即，如果它被埋在这些沉积物或回收和/或再活化，并释放到底层水再次。铁的地球化学循环是由生物和非生物反应的复杂相互作用驱动的，将铁循环与许多其他元素循环联系起来。我们对冰川峡湾中铁的地球化学循环如何影响密切相关的营养物质（如Si、P或Mn）的命运的理解也很有限。极地地区，特别是峡湾生态系统，正在经历气候变化的最显著影响。然而，到目前为止，只有少数研究将这些影响与峡湾沉积物的地球化学循环联系起来，因此对地球化学循环的实际影响，例如Fe循环，在很大程度上是未知的。在我以前的工作中，我可以表明，斯瓦尔巴特峡湾沉积物是陆地和海洋之间重要的活动界面，通过底栖生物循环将冰川Fe转化为潜在的生物有效Fe。然而，我也发现，冰川退缩有可能改变峡湾沉积物的地球化学，包括底栖铁循环，并降低峡湾沉积物的潜在生物可利用铁的来源。拟议项目的主要目的是确定的过程（生物和非生物）转化冰川来源的铁在峡湾沉积物中，量化的影响，这种转换的Fe，Si，P和Mn的命运，并评估潜在的后果冰川退缩。这将通过详细研究地球化学、铁矿物学和微生物学以及测量斯瓦尔巴特峡湾与海洋和陆地终止冰川（分别为Kongsfjorden和Dicksonfjorden）的断面中的铁通量和相关营养物质来完成。该项目的另一个目的是阐明冰川峡湾底栖铁转化的地理分布和相关性。因此，我将调查底栖铁循环在两个斯瓦尔巴特峡湾，邻近的大陆架以及峡湾在东格陵兰岛和南格鲁吉亚。我将与专注于远洋（Fe）地球化学的同事，地球化学家，微生物学家，古海洋学家和建模师一起工作，所有这些都致力于Fe地球化学的不同方面。这样，我们的工作将相互补充，我们将能够获得详细的了解冰川铁的数量和特性，以及运输和转化途径的沉积物和水柱。研究结果将有助于更好地了解冰川产生的营养物质从冰冻圈向海洋的转移，并有助于评估气候变化的潜在后果。

Glaciers are, along with rivers, hydrothermal vents and aeolian dust, known to be an important source of Fe, an essential but often limiting element for live in the ocean. However, up to 95 % of glacial Fe settles to fjord sediments close to the glacial source. It is currently not understood what the fate of glacial Fe is once it is exported to fjord sediments, i.e. if it is buried in these sediments or recycled and/or remobilized and released into the bottom water again. The biogeochemical cycle of Fe is driven by a complex interplay of biotic and abiotic reactions, connecting the Fe cycle to many other element cycles. Our understanding of how biogeochemical Fe cycling in glaciated fjords affects the fate of closely connected nutrients, such as Si, P or Mn, is also limited. Polar regions and especially fjord ecosystems are experiencing the most pronounced effects of climate change. However, only few studies so far link these effects to sedimentary biogeochemical cycles in fjords, so the actual effects on biogeochemical cycles, e.g. the Fe cycle, are largely unknown.In my previous work, I could show that Svalbard fjord sediments are important active interfaces between land and ocean, converting glacial Fe into potentially bioavailable Fe through benthic cycling. However, I also found that glacial retreat has the potential to change the biogeochemistry of fjord sediments, including the benthic Fe cycle, and decreases the potential of fjord sediments to be sources of potentially bioavailable Fe. The main aims of the proposed project are to identify the processes (biotic and abiotic) transforming glacially sourced Fe in fjord sediments, to quantify the effects of this conversion on the fate of Fe, Si, P and Mn, and to assess potential consequences of glacial retreat. This will be done by studying in detail the geochemistry, Fe-mineralogy and microbiology, as well as by measuring fluxes of Fe and connected nutrients in transects of Svalbard fjords with sea- and land-terminating glaciers (Kongsfjorden and Dicksonfjorden, respectively). A further aim of this project will be to elucidate the geographic distribution and relevance of benthic Fe-transformations in glaciated fjords. Therefore, I will investigate benthic Fe cycling in two more Svalbard fjords, the adjacent continental shelf as well as fjords in East Greenland and South Georgia. I will work together with colleagues focusing on pelagic (Fe) biogeochemistry, geochemists, microbiologists, paleooceanographers and modelers, all working on different aspects of Fe biogeochemistry. Such that our work will complement each other and we will be able to gain a detailed understanding of the amount and characteristics of glacial Fe, as well as transport and transformation pathways in the sediment and water column. The results will facilitate a better understanding of the transfer of glacially-derived nutrients from the cryosphere to the ocean and an assessment of potential consequences of climate change.