Supervisors: Dr Anna Hickman (UoS), Dr Eleanor Frajka-Williams (UoS), Dr Stephanie Henson (NOC), Jan Kaiser (UEA), Matthew Palmer (NOC)
CO2 taken up from the atmosphere by biological processes is transferred into the 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. Critically important is the depth at which particulate organic carbon (POC) is remineralised as it plays a key role in setting the air-sea balance of CO2. Despite its importance, our understanding of this pump is currently limited due to the need for ship-board observations, in particular observations of how POC remineralisation varies over timescales of days to months. New autonomous technologies are opening the door for long-term, high resolution observations of these sinking particles. Seagliders are unmanned autonomous vehicles that make measurements over weeks to months, several times per day and to depths of 1000 m, including optical backscatter data. This can be used to estimate particle properties, including their organic carbon content. The project will develop a novel methodology to robustly determine remineralization depth (and its temporal variability) from the standard suite of sensors typically integrated into gliders. This project will use a complete year of continuous glider data collected in the Northeast Atlantic, and additional datasets from neighbouring shelf seas, to investigate the seasonal evolution of particle abundance and remineralisation. The project will initially involve significant methodological development, followed by using the data to answer key questions such as whether POC flux and remineralisation are always in phase, or whether they can become decoupled; the timescales of variability in POC and remineralisation, e.g. associated with transient pulses; and what factors might affect when and how variability in POC and remineralisation occurs.
The student will initially develop a methodology for obtaining information on remineralization depth from the standard suite of glider sensors (oxygen, backscatter, temperature, salinity etc.). They will then analyse existing glider datasets of backscatter and ancillary environmental data from the Porcupine Abyssal Plain site and deployments undertaken during the Shelf Seas Biogeochemistry programme (UK shelf seas). To start the student will transform backscatter data into estimates of POC concentration and flux, benefitting from the expertise of other group members who have established protocols for processing, calibrating and interpreting other parameters in this dataset, such as chlorophyll and oxygen concentration. The scientific focus will be on the seasonal changes in POC remineralisation depth and controlling factors. Subsequent work may include exploiting additional autonomous technologies, such as the Bio-Argo float network, to broaden the study to larger scales. This will allow the student to assess whether the variability in other parts of the global ocean are likely to be similar to that observed in the Northeast Atlantic. Alternatively, the student may explore the mechanisms and patterns of variability in POC and remineralisation in global biogeochemical models, including climate change simulations.
The NEXUSS CDT provides state-of-the-art, highly experiential training in the application and development of cutting-edge Smart and Autonomous Observing Systems for the environmental sciences, alongside comprehensive personal and professional development. There will be extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial / government / policy partners. The student will be registered at University of Southampton, and hosted at the National Oceanography Centre Southampton in the Ocean Biogeochemistry and Ecosystems group. Specific training will include:
The Ocean Biogeochemistry and Ecosystems group is renowned globally as one of the leading centres of excellence in biological carbon pump research with plankton ecologists, numerical modellers, remote sensing specialists, theoreticians and particle flux geochemists working together to address the most significant problems in biological oceanography. Specific training will include: concepts in biogeochemical oceanography, processing and analysing autonomous underwater vehicle data, bio-optics, data synthesis and statistical skills. The student can attend appropriate university Masters lecture courses to gain relevant background knowledge if needed. Presentation of results at national and international conferences will be encouraged. The student will also have the opportunity to participate in a research cruise.
Background Reading:
Dall’Olmo and Mork (2014) Carbon export by small particles in the Norwegian Sea, Geophysical Research Letters, doi: 10.1002/2014GL059244
Omand et al. (2015) Eddy-driven subduction exports particulate organic carbon from the spring bloom, Science, doi: 10.1126/science.1260062
Henson et al. (2015) Variability in efficiency of particulate organic carbon export: A model study, Global Biogeochemical Cycles, doi: 10.1002/2014GB004965
To apply for this project, use the: apply for a NEXUSS CDT studentship