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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities

Lead Supervisor: Clara Manno, British Antarctic Survey

Co-Supervisors: Helen M. Williams, Earth Sciences; Kate Hendry, University of Bristol; Sophie Fielding, British Antarctic Survey

Brief summary: 
This project aims to understand the potential impact of increase in iron input in the Southern Ocean, as consequence of ice retreat, using an isotopic geochemistry approach.
Importance of the area of research concerned: 
The Southern Ocean accounts for one-third of anthropogenic CO2 uptake by the global ocean. The acceleration of ice loss in this region, as a consequence of global warming, may stimulate photosynthesis due to the release of iron (Fe) into the marine realm. Photochemical and biological reduction and dissolution of particulate Fe throughout the water column appear to be key processes in regulating its supply and bioavailability to marine biota (Tagliabue et al., 2019). The effects of Fe supply can potentially change both total production and the algal community structure, which may have large consequences for Southern Ocean carbon cycling and the uptake and transfer of atmospheric carbon dioxide (Boyd et al., 2010). In seawater, stable Fe isotopes can potentially be used to track Fe inputs and assess the relative importance of different sources of dissolved Fe to the oceanic reservoir. Similar to Fe, silicon (Si) seawater isotope variations are a powerful tool for investigating recycling processes due to the isotopic fractionation during diatom uptake in the euphotic zone, and diagenetic reactions in shallow seafloor sediments (Cassarino et al., 2020).
Project summary : 
Global warming is leading to considerable ice retreat in Antarctica resulting in enhanced iron input into coastal areas, potentially feeding ocean regions where phytoplankton growth is otherwise Fe-limited. West Antarctic Peninsula (WAP) shelf is one of the fastest warming regions at most risk from ice decline. Therefore, it is crucial to understand the main processes promoting CO2 uptake to forecast the potential impact of increased Fe input on biogeochemical cycling. Marguerite Bay, located on the WAP, is considered a ‘high recycling, low export’ region with blooms dominated by large diatoms, low transfer efficiencies to deep water, and intensive remineralisation and grazing in the upper water-column. This project aims to use Fe and Si isotope geochemistry to investigate the main drivers that regulate export and recycling in Marguerite Bay.
What will the student do?: 
The student will learn to use novel techniques to analyse Si and Fe isotope composition as a proxy for Fe and Si sources, transport and reaction pathways. Specific tasks: 1) Identify the biogenic and abiotic silica and Fe proportions in the Margaret Bay: Water samples from the shelf will be analysed for silica and Fe isotopes. 2) Assess the change on plankton and faecal pellets (zooplankton faces) seasonal isotopic signature: Tows samples will be investigate to detangle the role of plankton community structure in the change of recycles/export process during the season. 3) Investigate the seasonal and annual variability in sinking of particulate matter and its origin to on-shelf sediments: Sediment traps and sediment cores samples will be analysed for biogeochemical composition and isotopic compositions. There may be the possibility of fieldwork as part of a BAS long term observation programme, to take water samples and collect samples of zooplankton and settling material around Margaret Bay. However, should this not be possible, the PhD can be completed using archived samples already obtained by BAS.
References - references should provide further reading about the project: 
Ref 1. Tagliabue, A., Bowie, A. R., DeVries, T., Ellwood, M. J., Landing, W. M., Milne, A., ... & Boyd, P. W. 2019. The interplay between regeneration and scavenging fluxes drives ocean iron cycling. Nature communications, vol. 10, pp. 1-8
Ref 2. Boyd, P. W., and M. J. Ellwood (2010), The biogeochemical cycle of iron in the ocean, Nat. Geosci., vol. 3, pp. 675– 682
Ref 3. Cassarino, L., Hendry, K. R., Henley, S. F., MacDonald, E., Arndt, S., Freitas, F. S., ... & Firing, Y. L. 2020. Sedimentary nutrient supply in productive hot spots off the West Antarctic Peninsula revealed by silicon isotopes. Global Biogeochemical Cycles, vol. 34, e2019GB006486
You can find out about applying for this project on the British Antarctic Survey (BAS) page.
Clara Manno
Dr Helen Williams
British Antarctic Survey Graduate Administrator