Iron released from Antarctic ice controls the biological carbon pump in the surrounding Southern Ocean

Primary supervisor: Dr Angela Milne (University of Plymouth)

Secondary supervisor: Dr Simon Ussher (University of Plymouth)

Additional supervisors:

Dr Joanna Dixon (Plymouth Marine Laboratory) Email:

Dr Will Homoky, (University of Oxford). Email:

Scientific background

The Southern Ocean surrounding Antarctica accounts for nearly 40% of the global oceanic sink of anthropogenic carbon dioxide emissions. Understanding the mechanisms that regulate this carbon sink is fundamental in forecasting impacts on the Earth system under future climate change scenarios. 

The ocean’s ‘biological pump’ is integral to this carbon sink and consists of phytoplankton assimilating carbon dioxide into organic matter through photosynthesis. Iron is essential for the growth and productivity of phytoplankton and where it exists in deficient concentrations, such as the Southern Ocean, it controls the efficiency of this pump.

The overall aim of this project will be to assess the bioavailability of different iron sources and what effect these have on microbial growth. To achieve this, you will study iron availability from different end-member samples (e.g. glacial/sea-ice, seawaters and sediments) and, in conjunction with other oceanographic data (e.g. light/irradiance), form a better understanding of microbial responses to iron availability in this globally important region.

This project will provide an exciting and rare opportunity to study the transport and bioavailability of iron in the Southern Ocean and become part of a UK team studying this region as part of the NERC RoSES research programme.

Research methodology

Using clean handling techniques, you will collect seawater, particulate matter, glacial- and sea-ice samples during a shipboard expedition to Antarctica. Through bioassay experiments, the response of the in-situ microbial community to different iron sources will be investigated. 

To assess iron availability from collected particulates, in a shore-based laboratory you will perform sequential leach-digestions that you will analyse using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS).


You will become an expert trace-metal marine biogeochemist. In world-class laboratory facilities in Plymouth and Oxford, you will receive comprehensive training in clean handling and advanced analytical techniques which will be required to perform radiotracer bioassay experiments and respective analyses.

Person specification

We are looking for a highly self-motivated graduate with a BSc or Masters level degree in Earth, Ocean or Environmental Science, or Chemistry (or similar). You will be inquisitive and enjoy problem-solving with a genuine passion for marine science.


Iron (Fe) is a key requirement for biological production and has been shown to be a limiting nutrient in most Southern Ocean waters (Tagliabue et al. 2014). 

In the surface waters of the Weddell Gyre dissolved-Fe levels vary from 0.01-0.1 nM, but can increase up to ~1 nM over the continental shelf (Klunder et al. 2014). 

The main sources of this Fe include sediments and glacial/sea-ice melt on the shelf (Lin et al. 2011). Winter entrainment and upwelling in central gyre waters of dissolved-Fe from these sources may control the rate of primary production and thus carbon uptake in this region.

This project aims to assess the bioavailability of iron from different sources in the Weddell Sea region of Antarctica, and evaluate their relative importance against light another growth-limiting factor. 

Stable and radioisotopes (e.g. 18O, 224Ra) will establish end-member Fe sources while bioassay radiotracer experiments, incubated with source-Fe and exposed to varying light levels, will investigate in-situ microbial community responses (e.g. Zubkov et al. 2007). 

In a world where atmospheric CO2 concentrations continue to rise, evaluating important sinks of carbon and the factors that limit carbon uptake, is more relevant than ever before. Key findings from this project can be used to improve model predictions of future climate change scenarios.

Measurable objectives

(i) A review of the literature relating to the concentrations of Fe and productivity in the Southern Ocean, with a focus on the Weddell Sea.

(ii) Assessment of clean handling and analytical competency through the use of reference materials and standards, for Flow Injection Analysis, ICP-MS, and radiometric and isotopic analysis.

(iii) Determine and monitor phytoplankton growth, microbial activity and Fe concentrations in shipboard microbial bioassays using Southern Ocean and Weddell Sea waters incubated with end-member Fe-source samples (sea/glacial ice and sediments/particles).

(iv) Determine microbial iron uptake rates of microbial communities using radiotracers (55Fe), under varying light regimes.

(v) Evaluate the bioavailability of Fe from the different end-member sources in shore-based leaching experiments.

(vi) Assess the importance of Fe to productivity and microbial physiology by combining data from radiotracer incubations with productivity and physiological data (Chla, light, Fv/Fm). Evaluate/extrapolate the impact of Fe availability on carbon removal in the Southern Ocean.

Research methodology and management

This project is a unique opportunity for a student interested in the marine environment and climate. It will provide a first-class research experience investigating the chemistry of the Weddell Sea and how Fe availability impacts on biology and hence carbon sequestration. 

The interdisciplinary nature of the project and associated NERC RoSES-PICCOLO programme will allow plenty of scope for independent thinking and collaboration. 

There is a supportive postgraduate environment within the Biogeochemistry Research Group, where the student will be primarily based, through training on an additional research cruise (RoSES-CUSTARD) and placements at PML (for radiotracer work) and the University of Oxford will allow further scope for independent development.

Practical training will be provided by the supervisory team and supported by postdoctoral researchers in appropriate and well-equipped laboratories. Professional training (e.g. sea survival) will be provided by relevant external bodies. Regular supervisory meetings will ensure the progress and development of the student.


This project has been shortlisted for funding by the ARIES NERC Doctoral Training Partnership. Undertaking a PhD with ARIES will involve attendance at training events.

ARIES is committed to equality & diversity, and inclusion of students of any and all backgrounds. All ARIES Universities have Athena Swan Bronze status as a minimum.  

Applicants from quantitative disciplines who may have limited environmental science experience may be considered for an additional three-month stipend to take appropriate advanced-level courses.

Usually, only UK and EU nationals who have been resident in the UK for three years are eligible for a stipend. Shortlisted applicants will be interviewed on 26/27 February 2019.

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