Mechanisms and effects of benthic biogeochemical iron cycling in glaciated fjords

点击翻译按钮获取中文摘要

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.