Bloom and bust: seasonal cycles of phytoplankton and carbon flux

Rationale: 

CO2 taken up from the atmosphere by biological processes in the ocean is transferred into the deep ocean’s “twilight zone” mostly in the form of sinking particles.  Without this “biological carbon pump”, atmospheric CO2 would be 50% higher than it already is.  Despite its importance, our understanding of this pump is currently limited due to the scarcity of ship-board observations, in particular of how particulate organic carbon (POC) fluxes vary over time – on scales from days to seasons. However, now a growing network of underwater robots are opening the door for high-resolution observations of these sinking particles. Gliders are unmanned autonomous vehicles that make measurements over weeks to months, to depths of 1000 m, including optical backscatter data which can be used to estimate POC fluxes.  At one of the UK’s long-term observing sites, the Porcupine Abyssal Plain (https://projects.noc.ac.uk/pap/), we have collected data from multiple glider missions, including in collaboration with colleagues at NASA (https://oceanexports.org/).  These data will allow important, currently unresolved, questions to be addressed, such as: How do fluxes vary seasonally in relation to phytoplankton blooms? How episodic are the fluxes? What are the implications for characterizing global-scale organic carbon fluxes? (Bol et al., 2018; Henson et al., 2015) Filling this knowledge gap will allow better predictions of how this important planetary carbon flux is linked to primary production and how it responds to variability in the physical environment.

 

Methodology: 

The project will initially use data obtained from gliders during past missions at PAP, such as OSMOSIS in 2012-13 (Bol et al., 2018) and EXPORTS in 2021 (https://oceanexports.org/) to determine the temporal patterns in POC fluxes, their attenuation with depth, and how this relates to phytoplankton blooms.  An additional dataset will be available from the French APERO programme which will deploy gliders at the PAP site in summer 2023 (https://www.mio.osupytheas.fr/en/seas-and-oceans-global-change/apero-carbon-sequestration-ocean).  Glider-derived optical backscatter data profiles will be transformed into estimates of POC concentration and flux, using protocols established by co-supervisor Briggs (Briggs et al., 2020). Different metrics to characterise the fraction of POC flux reaching the mesopelagic zone will be calculated and compared.  Your initial analysis will focus on establishing the temporal patterns of phytoplankton blooms, flux and attenuation, before moving on to assessing how interannual variability in physical conditions may alter the relationship between primary production and fluxes.  Depending on your interests, subsequent work may include exploiting additional autonomous technologies to study particular processes, e.g. particle fragmentation (Briggs et al., 2020), or other locations in more detail, satellite data to broaden the study to larger spatial and temporal scales, or using global biogeochemical models (including climate change simulations) to explore the mechanisms and patterns of variability in POC fluxes

Location: 
NOC/UoS
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 National Oceanography Centre (Southampton). Specific training will include: use of autonomous platform data for biogeochemical studies, analysis of satellite data and model output, ocean biogeochemistry and its interaction with climate (e.g. IMBER ClimEco summer school). 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 appropriate university Masters level lectures to gain relevant background knowledge. Presentation of the results at (inter)national conferences will be encouraged. Collaboration with colleagues in the US and France associated with the EXPORTS and APERO programme will be encouraged. There will also be the opportunity to participate in a research cruise to the PAP site

Eligibility & Funding Details: 

Please see https://inspire-dtp.ac.uk/how-apply for details.

 

Background Reading: 

Bol, R., S. Henson, A. Rumyantseva and N. Briggs (2018), High-frequency variability of small-particle carbon export flux in the Northeast Atlantic, Global Biogeochemical Cycles, 32, 1803-1814, doi: 10.1029/2018gb005963

Briggs, N., G. Dall’Olmo and H. Claustre (2020) Major role of particle fragmentation in regulating biological sequestration of CO2 by the oceans, Science, 367 (6479), 791-793, doi: 10.1126/science.aay1790

Henson, S., A. Yool and R. Sanders (2015), Variability in efficiency of particulate organic carbon export: A model study, Global Biogeochemical Cycles, 29(1), 33-45, doi:10.1002/2014GB004965

 

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