The Southern Ocean ferrous wheel: multi-isotope proxies of iron cycling in the Antarctic overturning circulation

Project Summary: 

The Southern Ocean overturning circulation is an engine of our global carbon cycle and planetary homeostasis, characterized by the upwelling of nutrient rich waters that stimulate planktonic fixation of carbon dioxide from the atmosphere, and strong downwelling that enhances the export of carbon from the surface to the deep ocean for hundreds to thousands of years. However, the role of Southern Ocean overturning for planktonic cycling of carbon remains critically uncertain due to uncertain sources and cycling of its most biologically-deficient nutrient element, iron.

This project aims to characterise the vulnerability of the carbon cycle in the Southern Ocean to its changing sources of iron, by deconvolving isotopic signals of iron’s origin in the upper and lower limbs of the Antarctic overturning. Using a novel multi-proxy approach, you will pair state-of-the-art seawater iron isotope analyses with additional isotope proxies (including radium and oxygen isotopes) that are suited to disentangle and trace mixtures of hydrothermal, sedimentary and glacial sources in these regions.

Free Antarctica Ice photo and pictureA droplet of seawater undergoing isotope purification

Figure 1: Convoluted sources of iron derived from glaciers, sea ice, sediments and upwelling impact the oceans iron and carbon cycles (left). Multi-isotopes proxies my be used to deconvolve sources of iron for phytoplankton and expose the vulnerability of the Southern Ocean to active environmental changes.

You will use ultra-clean sample-handling procedures and advanced mass-spectrometry analytical techniques (Figure 1), and validate your data quality against world-class benchmarks for compliance and contribution to the International GEOTRACES programme.

You will benefit from a unique and ultra-clean seawater samples and their wide-ranging ancillary datasets collected as part of NERC’s strategically funded programme: RoSES (Role of the Southern Ocean in the Earth System). Through which, the component projects CUSTARD and PICCOLO have each sampled key regions of the Antarctic overturing circulation, and will integrate further with the latest NERC strategic aim to understand “Biogeochemical processes and ecosystem function in changing polar systems and their global impacts” (BIOPOLE). The unique samples we have made available to you for this project include deep waters of the upper limb of the ocean overturning circulation (CUSTARD), and shelf-slope and under-sea ice samples we are collecting from the lower limb of the overturning circulation following a record breaking year for global heating impact on the polar regions in January 2024 (PICCOLO). In addition, your project team is widely connected to active UK, international, and GEOTRACES marine science research activities in the Southern Ocean and elsewhere, so that future relevant samples and fieldwork opportunities to develop your project interest further may also become available.

Working environment

As a successful applicant, you will join Leeds’ Earth Surface Science Institute (ESSI); a medium-sized and friendly research institute that includes field- and laboratory-analytical geochemists, isotope geochemists and biogeochemists, as well as sedimentologists, palaeontologists and modellers of climate and biogeochemistry. The group holds several annual science and social events and weekly informal get-togethers. You will be supervised by a multi-talented team, led by Dr Will Homoky who’s research explores understanding of the modern ocean iron cycle, and uses stable and radioisotope tracers of biogeochemical pathways in the ocean. Further co-supervision and training will be provided in ESSI by Dr Alastair Lough, who is expert in marine trace element and isotope geochemical analyses in Leeds’ Cohen Research Cluster and our new Aqueous Analytical Facility’s Clean Laboratory; and ESSI Director Dr Tracy Aze, who is an expert in marine microbes and their response to environmental change.

Project partners

External to Leeds, Dr Tim Conway (University of South Florida, USA) is a specialist in high-precision seawater metal isotope analyses, and project CASE Partner. Tim will sponsor a funded PhD-placement and training opportunity in his Marine Metal Isotope and Trace Element (MarMITE) Laboratory at the University of Southern Florida, USA, and provide direct access to Multi-Collector-Inductively Coupled-Mass Spectrometry facilities in support of trace metal isotope analyses.

You will benefit further from our active programmatic research networks and collaboration opportunities. For example, Professor Michael Meredith (British Antarctic Survey) and Prof. Karen Heywood FRS OBE (University of East Anglia) are a celebrated leaders of polar marine science and experts in the application of oxygen isotopes as a tracer of melt water fluxes in oceanography – as a project partner and Executive Advisor to BIOPOLE, Prof. Meredith will offer NERC-funded access and expertise to oxygen isotope analyses. Prof. Heywood, and additional project partners Dr Angela Milne and Dr Simon Ussher (University of Plymouth) will also provide access to wide ranging ancillary data and regional insights into trace metal cycling through both CUSTARD and PICCOLO projects, and support your interpretations and integration of results within these programmes and networks.

Entry requirements

This project would suit somebody with a degree in one of the natural sciences (e.g. Earth, ocean or environmental science) or chemistry, and the candidate should have a strong interest in research of the Earth surface environments, ocean biogeochemistry and the applications of trace element and isotope geochemistry. Prior formal training in seawater trace element and/or isotope analytical techniques is not essential, but enthusiasm for these methods is advisable. All necessary training will be provided as part of the project.

Further information

If you have any further questions about the project please contact the lead supervisor, Dr Will Homoky Due to remote fieldwork in support of this project, supervisors Homoky and Lough will be in Antartica from January 12th to March 12th 2024. During this period, please also Cc’ Dr Tracy Aze for any project related correspondence to ensure it is received and responded to.