The benthic biogeochemical iron cycle in Arctic fjords
Glacial ice and subglacial meltwater is rich in lithogenic material, including iron, due to glacial comminution and subglacial weathering. Therefore, glaciers are an important source of iron to the ocean. Marine-terminating glaciers deliver iron via subglacial meltwater and through icebergs, which slowly melt during their travel through the fjord and ocean once they calved-off the glacier terminus. Much of the iron in glacially sourced material is particulate or will become particulate when in contact with oxic and saline fjord water, due to oxidation and flocculation processes. As a consequence, it is estimated that up to 95% of the glacially derived iron is settling in sediments close to the glacial source. Within these sediments, an interplay of abiotic and microbially mediated reactions, forming the benthic biogeochemical iron cycle, change the characteristics of glacially derived iron and thereby impact its fate, i.e. if it gets buried within the sediments or released to the overlying water.
The Arctic currently has the highest warming rate worldwide, leading to increasing rates of shrinking and retreating of glaciers. When glaciers retreat on land this changes the characteristics of glacially derived material, as meltwater flows through a proglacial river before entering the fjord. Glacial retreat onto land moreover changes overall fjord hydrology and biogeochemistry. Microorganisms are the key drivers of biogeochemical cycles, including the iron cycle, within these sediments. However, it is not well understood how their activity is controlled within these sediments and how this could be impacted by retreating glaciers. Understanding these controls and impacts is essential to make predictions about consequences of future changes.
The goal of my research is to better understand the role of fjord sediments as biogeochemically active interface, connecting glaciers and the oceanic shelf and open ocean, and how the function of microbial communities within fjord sediments and could change due to glacial retreat. The focus is on the benthic biogeochemical iron cycle, for several reasons. (i) Iron is a redox-active element and can be used by many microorganisms for energy generation and growth. (ii) The benthic iron cycle is connected to many other element cycles, such as the sulfur, carbon, or nitrogen cycle through different biotic and abiotic reactions. (iii) In the water column, iron is an important and often limiting nutrient for phytoplankton, while iron-rich fjord sediments have the potential to be a source of iron to the water column; therefore also studying benthic-pelagic coupling is essential. (iv) Moreover, the formation and dissolution of iron minerals within sediments controls the fate of other nutrients but also pollutants in the environment.
Current field sites of this project are located along the west coast of Svalbard and the east coast of Greenland. The field sites offer the possibility to study fjords with different glacial regimes and bedrock types, which enables us to understand how these factors impact the biogeochemistry of fjord sediments and how these systems could change with glacial retreat.
Related publications:
- Herbert LC, Zhu Q, Michaud AB, Laufer-Meiser K, Jones CK, Riedinger N, Stooksbury ZS, Aller RC, Jørgensen BB, Wehrmann LM (in review). Benthic iron flux influenced by climate-sensitive interplay between organic carbon availability and sedimentation rate in Arctic fjords.
- Laufer-Meiser K, Michaud AB, Maisch M, Byrne JM, Kappler A, Patterson MO, Røy H and Jørgensen BB. Potentially bioavailable iron produced through benthic cycling in glaciated Arctic fjords of Svalbard. Nature Communications, 12, 1349. DOI: https://doi.org/10.1038/s41467-021-21558-w
- Jørgensen BB, Laufer K, Michaud, AB, Wehrmann, LM (2021). Biogeochemistry and microbiology of high Arctic marine sediment ecosystems – case study Svalbard fjords. Limnology and Oceanography 66,273-292.
- Herbert LC, Riedinger N, Michaud AB, Laufer K, Røy H, Jørgensen BB, Heilbrun C, Aller RC, Cochran KJ, Wehrmann LM. 2020. Glacial controls on redox-sensitive trace element cycling in Arctic fjord sediments (Spitsbergen, Svalbard). Geochim. Cosmochim. Acta 271: 33–60. DOI: 10.1016/j.gca.2019.12.005
- Michaud AB, Laufer K, Findlay A, Pellerin A, Antler G, Turchyn AV, Røy H, Wehrmann LM and Jørgensen BB (2020). Glacial influence on the iron and sulfur cycles in Arctic fjord sediments (Svalbard). Geochimica et Cosmochimica Acta. DOI: 10.1016/j.gca.2019.12.033
- Carlson DF, Pasma J, Jacobsen ME, Hansen MH, Thomsen S, Lillethorup JP, Tirsgaard ST., Flytkjaer A, Melvad C, Laufer K, Lund-Hansen C, Meire L, Rysgaard S. (2019) Retrieval of Ice Samples Using the Ice Drone. Frontiers in Earth Science, Vol. 7, p. 287. DOI: 10.3389/feart.2019.00287
- Laufer K, Michaud AB, Røy H and Jørgensen BB. (2020) Reactivity of Iron Minerals in the Seabed Toward Microbial Reduction – A Comparison of Different Extraction Techniques. Geomicrobiology Journal, 37:2, 170-189. DOI: 10.1080/01490451.2019.1679291
- Buongiorno J, Herbert L, Wehrmann L, Michaud AB, Laufer K, Røy H, Jørgensen BB, Szynkiewicz A, Faiia A, Yeager K, Schindler K, Lloyd K. (2019) Complex microbial communities drive iron and sulfur cycling in Arctic fjord sediments. Applied and Environmental Microbiology. DOI: 10.1128/AEM.00949-19
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