Controls on Dissolved Iron Distributions in the Southern Ocean

  • Supervisors: Dr Hannah Whitby, University of Liverpool
    Prof Alessandro Tagliabue, University of Liverpool

  • External Supervisors: Dr Hélène Planquette, CNRS, (Uni Western Brittany)
    Dr Géraldine Sarthou, CNRS, (Uni Western Brittany)
  • Contact:

    Dr Hannah Whitby (University of Liverpool),

  • CASE Partner:

Application deadline: 10 January 2020


The Southern Ocean plays a crucial role in mediating climate, with around 50% of ocean CO2 uptake occurring south of 30°S (Majkut et al., 2014). It is subsequently one of the most sensitive regions to climate change (IPCC, 2014). Linking the three main ocean basins (Atlantic, Indian and Pacific), the Southern Ocean is a hub of salt, heat and element transport in which nutrients and trace metals arriving at depth are upwelled, before being transformed by biological processes. 

As one of the key micronutrients to marine microorganisms, low concentrations of dissolved iron limit primary production in around half of the ocean surface (Moore et al., 2001). Ligand complexation is crucial for maintaining iron in solution where it can be taken up by microorganisms (Bruland et al., 2014). This complexation can control dissolved iron distributions, with the concentrations of iron binding ligands in biogeochemical models significantly impacting atmospheric CO2 calculations (Tagliabue et al., 2016). Examples of one of these ligand types are humic substances. Terrestrial-derived humics often dominate iron complexation in coastal waters, while their stability allows iron to be transported long distances by ocean currents (Muller, 2018). Humic material is also produced in situ in the marine environment (Romera-Castillo et al., 2011) Humics may thus play a crucial role in controlling oceanic dissolved iron distributions and their availability to microorganisms. However, their role in iron complexation in the open ocean is currently unclear, particularly in the under-sampled Southern Ocean, a key iron-limited region far removed from terrestrial inputs. 

Project Summary:

The aim of this PhD subject is to ascertain the controls on dissolved iron distributions in the Southern Ocean, including the role of humic substances. The supervisory team utilises laboratory, field and modelling experiments to understand the drivers of ocean biogeochemistry in general, with a focus on the controls on dissolved iron distributions in particular. The aim of the studentship will be to measure iron speciation and humic substances in the Southern Ocean using electrochemical techniques. Samples were collected during the SCALE Southern Ocean winter and spring cruises, and additional samples will be collected during the upcoming SWINGS cruise planned for early 2021. In addition to gaining expert skills in marine biogeochemistry and trace metal clean techniques, there will be an opportunity to participate on forthcoming research cruises to the Southern Ocean (e.g. SWINGS, GEOTRACES Section GS02, planned in early 2021 on N/O Marion Dufresne) and/or visit LEMAR laboratory in Brest, France depending on the interests of the candidate. There will be the opportunity to implement the results in a biogeochemical model depending on the interests of the student. 

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 biogeochemical background and basic chemistry skills. No previous experience of fieldwork or marine processes is required, as relevant training will be provided.


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

Majkut et al., 2014. Phil Trans. Roy. Soc.

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

Muller, 2009. Frontiers in Earth Sci.

Romera-Castillo et al., 2011. Applied and Environmental Microbiology, 77(21): 7490-7498.

Tagliabue et al., 2016. Global Biogeochemical Cycles, 30(2): 149-174.

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