Southern Ocean Iron Supply: Does Size Fractionation Matter?

Dr Amber Annett, Dr Kate Hendry, BAS

The Southern Ocean plays a disproportionately important role in ocean carbon drawdown, accounting for >40% of global anthropogenic C uptake, due to physical and biological processes. This biological component is limited in many Southern Ocean regions by scarcity of iron (Fe). Although the deep waters of the western Antarctic Peninsula (WAP) are crucial in supplying Fe to waters downstream, we have a poor understanding how Fe is stabilised during transport, and how much different Fe phases (soluble, colloidal, particulate) contribute to deep water inventories. Moreover, it remains unclear how the generation of different size fractions of Fe in sediments, and their subsequent release, is linked to hotspots of surface productivity and interactions with different sedimentary components such as silica.

The WAP is the fastest warming region of the southern hemisphere, and the impacts on Fe transport in a changing climate is unknown, hindering predictions of how the downstream drawdown of atmospheric carbon will change in the future. This project will use novel radium-based approaches to address the key questions: (1) What phases of Fe are most stable in deep shelf waters, and what are the implications for large-scale transport? (2) Is the stability of iron linked to hotspots of remineralization? 


Using a sample set previously collected from the northern Antarctic Peninsula, this project will investigate the distribution of iron within different size fractions (soluble, colloidal, particulate) from sediment porewaters to offshore water column, via flow-injection analysis, digestions and leaches, and the state-of-the-art inductively-coupled mass spectrometry facilities at the University of Southampton. To understand how the intensity of sedimentary remineralisation influences iron size fractionation, these results will be coupled with dissolved and particulate distributions and isotope signatures of silicon within sediment cores. Auxiliary data available will include carbon cycling, flux estimates from naturally-occurring radioisotopes, and hydrographic data. A future expedition is planned that will provide at-sea training, and an opportunity for the student to elucidate specific mechanisms in detail, guided by preliminary results.


The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at the School of Ocean and Earth Science. The student will also interact with co-supervisors at the British Antarctic Survey (BAS).

The student will learn to critically evaluate published research, and identify gaps and problems in their field. The student will learn to analyse the data, interpret the results and present their finding through scientific writing (thesis, peer-reviewed publications) and presentations to fellow researchers and wider community.   

Specific training will include:

·         Training in ICPMS.

·         Training in flow injection analysis

·         Training in non-traditional isotope geochemistry (silicon isotopes)

·         Training in the sampling of ocean waters for trace metal analysis according to GEOTRACES protocols, and in sediment sampling and processing

·         Statistical analysis, data acquisition and evaluation techniques

There may be opportunities to undertake fieldwork to sample water column and sediments, including a multidisciplinary expedition in the Southern Ocean.

Eligibility & Funding Details: 

Please see for details.


Background Reading: 

1.    Annett, A.L., J. Fitzsimmons, M. Lagerström, M. Séguret, M.P. Meredith, O. Schofield, R.M. Sherrell. (2017) Controls on dissolved and particulate iron distributions in surface waters of the Western Antarctic Peninsula shelf. Marine Chemistry, 196: 81-97.

Cassarino, L., K.R. Hendry, S.F. Henley, E. MacDonald, S. Arndt, F.S. Freitas, J. Pike, Y.L. Firing. (2020) Sedimentary nutrient supply in productive hotspots off the West Antarctic Peninsula revealed by silicon isotopes. Global Biogeochem. Cycles, 34.