Controls on Iron Bioavailability to Arctic Microorganisms


  • Supervisors: Dr Hannah Whitby, University of Liverpool
    Prof Claire Mahaffey, University of Liverpool


  • External Supervisors: Prof Maeve Lohan, (University of Southampton)
    Dr Julie Robidart, NOC Southampton
  • Contact:

    Dr Hannah Whitby (University of Liverpool), hannah.whitby@liverpool.ac.uk

  • CASE Partner:

Application deadline: 10 January 2020

Introduction:

The Arctic Ocean is a key region for global ocean productivity, but limitations on biological growth in Arctic waters are still poorly understood. Primary production is limited by a lack of dissolved iron across around half of the ocean surface (Moore et al., 2009). Over 99% of dissolved iron in seawater is bound to organic ligands, which control the concentration and distribution of iron throughout the ocean (Bruland et al., 2014). Such ligands can be terrestrially-derived or produced in situ, with some riverine inputs transporting iron long distances (Hioki et al., 2014, Slagter et al., 2017). Parts of the Arctic Ocean do however suffer seasonal iron limitation. For example, iron concentrations could limit under-ice phytoplankton blooms, which may have wider implications as ice retreats (Rijkenberg et al., 2018). Arctic microorganisms must therefore survive in iron-limited waters with sporadic iron input events from a variety of marine and terrestrial sources. However, the factors influencing the production and degradation of iron-binding ligands, and thus the bioavailability of iron to microorganisms, are still poorly constrained. 

Manipulation experiments with cultured representatives have revealed molecular mechanisms for iron acquisition and potential biomarkers that are diagnostic for iron stress, as well as assimilation of various forms of iron (e.g. Chappell et al., 2010). Field experiments using natural assemblages of plankton can use the relative abundances of these biomarkers in order to learn about iron physiology in situ. Combining this with iron speciation measurements provides a unique opportunity to further our understanding of iron limitation in this region.

Project Summary:

This PhD subject has two goals: 1) to understand how ligand source influences iron bioavailability and 2) to ascertain whether iron stress can be detected by changes to the ligand pool produced in situ. These goals will be achieved by measuring iron speciation in samples taken from Arctic estuaries using electrochemical techniques, followed by bioassay experiments during the N-Arc cruise in the Barents Sea and Fram Strait during summer 2021. Samples will be taken from temperature and light controlled trace metal clean bioassays to provide additional insights into the response of Arctic diazotrophs to nutrient, dissolved organic matter (DOM) and iron amendments. The responses observed in the bioassays will be compared to water column samples. RNA sequencing of the microbial communities in these experiments will be used to understand species-specific iron stress and utilisation. 

The supervisory team specialises in nutrient and trace metal chemistry, utilising field and laboratory experiments to understand the drivers of ocean biogeochemistry. In addition to gaining expert skills in marine biogeochemistry and trace metal clean techniques, there will be an opportunity to participate on upcoming research cruises to the Arctic Ocean (e.g. N-Arc Project planned for summer 2021). 

This project would be ideal for a student interested in global biogeochemical cycles, marine chemistry and climate change. Applicants must have a Bachelor’s degree in a relevant field, with Master’s degree desirable. Ideally, the candidate will have a chemical or biological background. No previous experience of fieldwork or marine processes is required, as relevant training will be provided.

References:

Bruland et al., 2014. Controls of Trace Metals in Seawater. Treatise on Geochemistry (Second Edition). Elsvier. Oxford: 19-51.

Chappell and Webb, 2010. Env. Micro. 12, 1, 13-27.

Hioki et al., 2014. Scientific Reports, 4: 6775.

Moore and Doney, 2009. Nat. Geo. 2, 867.

Rijkenberg et al., 2018. Front. Mar. Sci., 5, 88.

Slagter et al., 2017. Mar. Chem. 197, 11-25.

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