Shelf seas as sources and sinks of the greenhouse gases nitrous oxide, methane and carbon dioxide.

The atmospheric content of the long-lived greenhouse gases carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) has been increasing since the industrial revolution, largely as a result of human activity. These increases lead to global warming and ocean acidification, the latter by net ocean uptake of CO2. Shelf seas play an important role in the global carbon and nitrogen cycles. Biological production in seasonally stratified shelf seas removes CO2 from the atmosphere and the fixed carbon can subsequently be exported to the adjacent deep ocean, a process known as the shelf-sea carbon pump. Shelf seas are sources of CH4 and N2O to the atmosphere, but the magnitude and the variation of these emissions are highly uncertain. The production of CH4 and N2O counteracts the climate benefits of the shelf-sea carbon pump. Climate change, eutrophication, hypoxia and ocean acidification may affect the air-sea fluxes of the three gases in shelf seas. This ambitious PhD project aims to quantify the sources and sinks and their seasonal variation for the three greenhouse gases in the Greater North Sea and the Celtic Sea, as well as to understand the underlying physical, chemical and biological processes. New, high-precision, integrated cavity output spectroscopy analysers now allow the simultaneous measurement of all three gases. An autonomous shipboard system for continuous analysis of CH4, N2O and CO2 concentrations in surface water and marine air will be installed and operated for 1.5 year on the Cefas Endeavour, a research vessel which operates in the Greater North Sea and the Celtic Sea. The MEMENTO and SOCAT synthesis products will provide additional, historic data for the greenhouse gases. Ancillary parameters (sea surface temperature, salinity, fluorescence) will help identify processes associated with greenhouse gas hotspots in the shelf seas. Greenhouse gas measurements will be combined with satellite and reanalysis data (wind speed, sea surface temperature, ocean colour, mixed layer depth) and a mapping technique (multiple linear regression) for quantification of air-sea gas fluxes and their seasonal variation. The state-of-the-art project brings together highly experienced scientists at the Centre for Environment, Fisheries and Aquaculture (Cefas) and the University of East Anglia (UEA). It combines UEA's expertise in marine biogeochemistry with Cefas' knowledge of and access to UK shelf waters. The PhD student will collaborate with scientists at the Cefas' Marine Climate Change Centre to obtain policy-relevant information from this research and will publish several high-impact, scientific publications and a PhD thesis. NERC Industrial CASE students are fully integrated into the training of the Environment East NERC Doctoral Training Partnership (EnvEast DTP), that UEA leads. The project invests in world-class research and skill by training an exceptional member of the next generation of research and business leaders. The main beneficiaries of this timely research are global climate scientists, policy makers and the general public. The 1.5-year time series of air-sea fluxes of the three greenhouse gases in the Greater North Sea and the Celtic Sea will provide an essential benchmark against which future changes can be identified. This PhD project presents key steps towards a new generation of autonomous, high-precision instruments for N2O, CH4 and CO2 for operational use on ships of opportunity and will therefore be of direct benefit to the European Integrated Carbon Observation System. This research complements the UK Shelf Sea Biogeochemistry and Greenhouse Gas Emissions and Feedbacks programmes. The results will feed into regional and global biogeochemical models and the Global Methane and Carbon Budgets via data submission to MEMENTO and SOCAT. Such modelling and greenhouse gas accounting inform assessments by the Intergovernmental Panel on Climate Change and (inter-)national marine and climate change policy.