PLEASE NOTE: Application deadline date 08 Jan 2024. Applications are no longer being accepted for this project
Project Overview
The depth in the ocean at which sinking organic carbon is remineralised back into CO2 is crucial to setting atmospheric CO2 concentration. In this project, you will explore the links between remineralisation depth, particle size and plankton size by building a simple mechanistic model on the basis of global datasets.
Project Description
The size and shape of sinking particles is likely key to determining their remineralisation depth, as slower sinking particles are likely to be remineralised at a shallower depth. This leads to a “particle size-remineralisation feedback” hypothesis (Leung et al., 2021), such that under climate change-driven warming conditions plankton size structure shifts to smaller organisms due to increasing stratification, which leads to a shift to smaller sinking particles and so shallower remineralisation of organic carbon and nutrients. This latter would then increase nutrient availability in the upper ocean, which could drive increased primary production and carbon flux. The overall effect would be a dampening of the expected decline in primary production and carbon flux as a result of climate change. If correct, then current IPCC projections, which omit this potential negative feedback, are overestimating reductions in future ocean carbon storage (Henson et al., 2022). We will test this hypothesis by using existing public databases (e.g. Clements et al., 2023) to explore the relationship between the size of phytoplankton and the size, type and shape of sinking particles, and the links to remineralisation depth. We will build a simple mechanistic model incorporating (dis)aggregation, remineralisation and sinking to gain understanding of how different processes change the particle size spectrum. We will incorporate the effects of environmental factors such as temperature and oxygen concentration, so that we can make predictions about the impacts of climate change. The student will be embedded in a large international consortium project of carbon cycle scientists: https://exeterdesignstudio.co.uk/calipso/#
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 National Oceanography Centre, Southampton. Specific training will include use of autonomous platforms, satellite data, model output analysis, ocean biogeochemistry and interaction with climate. The student will develop skills in the in-demand areas of quantitative analysis of climate- and environment-relevant data. The student will be part of the Ocean BioGeosciences group at NOC, which is renowned globally as a centre of excellence in biological carbon pump research. The student may attend university Masters level lectures to gain relevant background knowledge. There will also be the opportunity to participate in a research cruise, likely in the North Atlantic.
Clements, D. J., Yang, S., Weber, T., McDonnell, A. M. P., Kiko, R., Stemmann, L., & Bianchi, D. (2022). Constraining the particle size distribution of large marine particles in the global ocean with in situ optical observations and supervised learning. Global Biogeochemical Cycles, 36, e2021GB007276. https://doi.org/10.1029/2021GB007276
Henson, S., C. Laufkoetter, S. Leung, S. Giering, H. Palevsky and E. Cavan (2022), Uncertain response of ocean biological carbon export in a changing world, Nature Geoscience, 15, 248-254, doi: 10.1038/s41561-022-00927-0
Leung, S. W., Weber, T., Cram, J. A., and Deutsch, C. (2021). Variable particle size distributions reduce the sensitivity of global export flux to climate change, Biogeosciences, 18, 229–250, https://doi.org/10.5194/bg-18-229-2021
