Autonomous carbon system observations from gliders (AutoCarb)

Rationale
The oceans and in particular coastal shelf seas are one of the main sinks of anthropogenic CO2, but the resulting acidification (pH decrease) has detrimental impacts on many marine biota. The development and implementation of affordable and accurate sensors on autonomous platforms to measure carbon-system related parameters such as pH, total alkalinity, the total dissolved inorganic carbon concentration (sum(DIC)) and the partial pressure of CO2 (p(CO2)) in shallow and deep waters are therefore a key requirement for future marine science.
This project combines expertise in the Ocean Technology and Engineering Group (OTE) at NOC with the track record of UEA's glider group in pioneering sensor integration into ocean gliders, supported by NEXUSS-partner Cefas as a major stakeholder and user of sustained observations in UK waters.
The contribution of the North Sea to CO2 uptake and export to the deep Atlantic (the shelf sea carbon pump) is a major uncertainty in the climate system and UK carbon budget. Transfer of carbon-enriched water across the northern boundary is recognised as a key factor, but is not well quantified. This project will develop sensors on gliders to provide high-resolution data to begin closing this gap and provide carbon flux estimates.

Methodology
The student will integrate mature pH sensors developed by OTE into underwater gliders. This will be followed by total dissolved inorganic carbon and total alkalinity sensors as they move from prototype to mature technology with the assistance of the student. After bench-top calibrations and tank-based tests, the performance of the complete package will be characterised in deployments of increasing duration during regular Cefas cruises. Discrete bottle samples will be taken to validate the sensor data, and their temperature, salinity and pressure dependence. This will quantify stability, accuracy, precision, power consumption and the effects of biofouling. Discrete samples will be supplemented by regional empirical relationships between total alkalinity and salinity, temperature, O2 and chlorophyll a concentrations to fill data gaps.
During the latter part of the project, a longer deployment along the major North Sea inflow will measure patterns and variability of Atlantic inflows. Empirical relationships between pH, sum(DIC), total alkalinity and other glider data (salinity, temperature, optical backscatter, O2, chlorophyll a and CDOM concentrations) will be used to characterise scales of variability in the carbon system. This will inform the design of future large-scale experiments to fully constrain carbon fluxes in a highly dynamic shelf-sea system.

Training
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. Specific training will include: Development and use of state-of-the-art chemical sensor techniques, electronics and mechanical engineering design, marine robotics, numerical and computing skills and analysis of large data sets ('Big Data', Unix, Matlab, time series analysis), specialist training in oceanographic fieldwork and instrument deployment, safe working practice, piloting and recovery of underwater gliders; analytical techniques for precise and accurate measurement of total alkalinity and dissolved inorganic carbon concentrations in seawater; theory of the ocean carbonate system; attendance of relevant summer schools (e.g. EGO network - Everyone's Gliding Observatories), presentations and international conference and postgraduate fora (such as the 'DISsertations in Chemical Oceanography' meetings).