About the Project
Project Rationale:
The importance of sediment processes in driving biogeochemical cycles, from blue carbon storage, to nutrients (silica, iron) and pollutants (lead, arsenic), are becoming increasingly recognized, from local to global scale [1]. However, accurately measuring fluxes from marine sediments presents a significant challenge as classical approaches (incubations, pore water gradients) focus on small scale diffusive processes, whereas sediment fluxes also depend on large scale and heterogeneous abiotic processes (e.g. temperature, tides, currents) and macrofaunal activities such as sediment reworking (bioturbation) and burrow ventilation (bioirrigation).
The aim of this study is to employ a cutting-edge radioisotopic disequilibrium approach [2] to quantify nutrient and pollutant fluxes from marine sediments across a range of future environmental settings such as climate warming and ocean acidification. This will be achieved by quantifying benthic fluxes around the UK across varying sediment types, associated macrofaunal communities, and differing levels of anthropogenic influence [3]. A key focus will be the comparison of the factors determining micronutrient flux between temperate UK waters and the western Antarctic Peninsula, where changing circulation is bringing increasing heat to the bottom waters of the shelf.
Methodology:
Isotopes of Ra are especially useful tracers of lithogenic inputs, produced from particle reactive thorium, thus distributions of Ra show a strong source from shelf sediments. The student will identify suitable locations for sediment core collections from around the UK, to provide a spatial and temporal survey with which to identify the key environmental and biological factors influencing sedimentary release of across a natural gradient of nutrient and pollutant elements. Analysis of radium-thorium disequilibrium in sediments will be used to determine fluxes, and contrasted with flux estimates derived from conventional methods. The student will assess macrofaunal activities in sediments using fluorescent sediment profile imaging techniques (fSPI) [3] and Presense oxygen optodes. The student will participate in a 16-day research cruise to the western Antarctic Peninsula, as part of the NERC-funded RaCE:TraX (Radium in Changing Environments: Tracing Fluxes) project. This study will combine geochemical sediment flux approaches with biological and ecological perspectives to provide a novel and holistic understanding of the role of sedimentary processes in biogeochemical cycling in a changing ocean.
Training:
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. Specific training will include:
• Working at sea and developing practical skills (including radioisotope methods and trace metal sampling techniques using GEOTRACES protocols).
• Training in the analysis of dissolved radium isotopes by delayed coincidence alpha counting
• Training in state-of-the-art analytical techniques including inductively coupled plasma mass spectrometry (ICP-MS) for accurate and precise analysis of dissolved trace elements. Analytical work will be undertaken in our world-class trace metal clean facilities.
• Training in experimental design and statistical analyses, R-programming
• Techniques required for quantifying macrofaunal activities in terms of sediment mixing and burrow irrigation (using fSPI, bromide and Presense oxygen optodes)
• Presenting research findings at international and national conferences.
Funding Notes
You can apply for fully-funded studentships (stipend and fees) from INSPIRE if you:
Are a UK or EU national.
Have no restrictions on how long you can stay in the UK.
Have been 'ordinarily resident' in the UK for 3 years prior to the start of the project.
Please click http://inspire-dtp.ac.uk/how-apply for more information on eligibility and how to apply
References
[1] Homoky, W.B., et al. 2016. Quantifying trace element and isotope fluxes at the ocean–sediment boundary: a review, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. https://doi.org/10.1098/rsta.2016.0246
[2] Shi, X., et al. 2019. Large benthic fluxes of dissolved iron in China coastal seas revealed by 224Ra/228Th disequilibria. Geochim. Cosmochim. Acta 260, 49–61. https://doi.org/10.1016/j.gca.2019.06.026
[3] Godbold et al. (2017) Vulnerability of macronutrients to the concurrent effects of enhanced temperature and atmospheric pCO2 in representative shelf sea sediment habitats. Biogeochemistry 135: 89-102.