Southern Ocean carbon pump vulnerability to changing iron supply

Aim of the PhD project

Your aim will be to understand the vulnerability of Southern Ocean biological carbon pump to potential changes in iron supply that will result from climate-forced environmental changes.

Image credits: The Southern Ocean (Left) William Putnam and Arlindo da Silva, NASA / Goddard Space Flight Centre; Sampling equipment in the Weddell Sea (Centre) Will Homoky / British Antarctic Survey; Seawater purification for analysis (Right) Will Homoky and Alastair Lough / University of Leeds

Background science

The Southern Ocean’s Antarctic Circumpolar Current and overturning circulation is the largest transport of water on Earth, characterised by the upwelling of nutrient-rich waters that stimulate planktonic growth. This growth plays a critical role in ocean’s uptake of carbon dioxide from the atmosphere and combines with strong downwelling of Southern Ocean currents to create an effective carbon pump – making the Southern Ocean an engine of our global carbon cycle and modern planetary-homeostasis – but understanding it’s response to future change relies on an accurate depiction of nutrient supply and recycling within it. Since the most-biologically deficient nutrient element, iron, enters the Southern Ocean from different ‘external’ sources (e.g. sediments, glaciers, dust and seafloor volcanism) each with varied sensitives to projected future warming, there is an urgent need to understand the biological dependency on iron supplied to Southern Ocean from these environments.

What the research involves

You will measure spatial patterns in the isotopic composition of iron present in seawater and develop predictive framework to determine the balance between external sources of iron and internally recycled sources of iron that are used fuel phytoplankton growth. This will cover key Southern Ocean regions, reflecting varied phytoplankton community compositions and nutrient mixtures in the present day. Using your results, you will be able to test assumptions and make predictions about iron-mediated impacts of climate change on the ocean biological carbon pump.   Your project will benefit from a unique existing sample set, as well as an opportunity to collect additional samples from ship-based fieldwork in Southern Ocean and Antarctic coastal waters. You will have ultra-clean seawater samples and wide-ranging ancillary data at your disposal, which were recently collected as part of the NERC’s RoSES Programme (Role of the Southern Ocean in the Earth System)  and it’s component projects CUSTARD and PICCOLO, which sampled key and never before-sampled regions of the Antarctic overturning circulation. These include deep waters of the upper limb of the ocean overturning circulation, and shelf-slope and the first under-sea ice samples of the kind collected from the lower limb of the overturning circulation in January 2024. In addition, members of your supervisory team have a future-funded fieldwork opportunity for a successful candidate to join a field-sampling plan across the Drake Passage and down the Western Antarctic Peninsula aboard the Royal Research Ship Sir David Attenborough.

Working environment

You will work with supervisors Dr Will Homoky and Dr Alastair Lough in Leeds’ School of Earth and Environment and Earth Surface Science Institute. Will and Alastair are experts in the ocean’s iron cycle, who’ve lead the development of iron isotopes as tracers of input and biogeochemical cycling in the ocean. They will provide your training in the purification and analysis of trace elements and your preparations for isotope analysis in Leeds’ Aqueous Analytical Laboratories, where you’ll have access to ISO Class-5 clean lab facilities, and state-of-the-art sample preparation (ESI seaFAST-LTR), and analytical capabilities (Triple-Quadrupole ICP-MS). As part of your project team, Dr Tim Conway (Associate Professor, University of South Florida, USA) is a renowned specialist in high-precision seawater metal isotope analyses, and offers you direct access to his Multi-Collector-Inductively Coupled-Mass Spectrometry (MC-ICP-MS) facilities in support of your iron isotope analyses of the samples prepared in Leeds. Tim will also offer further training opportunities a secondment to his Marine Metal Isotope and Trace Element (MarMITE) Laboratory at the University of Southern Florida, USA (*see below)

A successful applicant will be a welcome addition to our thriving NERC programmatic collaboration and research networks. Co-supervisors, Dr Angela Milne and Dr Simon Ussher (University of Plymouth) will provide access to wide ranging ancillary data and regional insights to dissolved-particulate trace metal cycling from both the CUSTARD and PICCOLO projects to aide your interpretation and publication of your findings. Professor Alessandro Tagliabue (University of Liverpool), completes your supervisory team; Alessandro is biogeochemist and modeller of the ocean’s iron cycle, with whom you can use your iron-isotopic framework to advance new model projections of iron-mediated Southern Ocean responses to climate forcing.

The project aligns directly to the NERC priorities areas to push the frontiers of understanding of our environmental health, it’s resilience to change, and to working in partnership to tackle complex environmental challenges, while ensuring we support the pipeline of talent with skills required to resolve future challenges. The project will benefit from seawater samples and their wide-ranging ancillary datasets already collected as part of NERC’s RoSES Programme (Role of the Southern Ocean in the Earth System). Through this, the component projects CUSTARD and PICCOLO have each sampled key regions of the Antarctic overturning circulation that are needed to support the proposed objectives. Your project will form an integral addition to a thriving research community studying polar ocean biogeochemical connections to Earth’s atmosphere and climate evolution.

*Project partner support:

1) Travel and Accommodation for up to 2 visits from Leeds to University of South Florida (for a maximum total period of 3 months, and equivalent cost of USD$5000)

2) A training and placement opportunity to join the Marine Trace Element and Isotope Laboratory Group at USF, with direct (free of charge) access to clean laboratories and Multi-Collector ICP analytical facilities in support of analyses for the duration of the PhD project under the supervision of Dr Tim Conway (equal to in-kind contribution towards RTSG worth more than USD$10,000).

Further information

Dr Will Homoky can be reached at w.homoky@leeds.ac.uk for any questions about this project.