Opportunities and risks to climate mitigation using seabed carbon stores: insights from the Convex Seascape Survey

Limiting global warming to below 2^oC will require the use of nature-based solutions for carbon capture at vast scales. With terrestrial vegetation carbon sinks faltering due to the impacts of heat, drought and wildfire, interest in marine carbon sinks is growing. The seabed represents an enormous carbon sink due to the burial of organic matter in ocean sediments, especially fine-grained muds. These carbon stores, built over thousands of years, are not impregnable, however, being at risk of remobilisation and remineralisation into CO₂ by industrial activities. For over 200 years, the seabed of coastal continental shelves has become increasingly disturbed by bottom fishing using trawls and dredges, channel excavation for ports and harbours, aggregate extraction, cable laying, offshore oil, gas and wind energy. Scientific research indicates that these activities release stored organic carbon, creating emissions to the ocean and atmosphere. But determining their magnitude is complex and results obtained to date are therefore highly controversial. Resolving this debate requires new, highly multidisciplinary science. The Convex Seascape Survey is a five-year global programme of over 20 institutions and more than 120 experts dedicated to understanding the seabed carbon of continental shelves, quantifying the risks it faces from human activities, and publishing open access data to maximise the reach and value of the insights gained. This presentation will describe how the project is combining expertise from multiple fields to generate detailed maps of ocean carbon distribution, identify the origins of these deposits, and quantify how they have been altered by centuries of human industrial use. The talk will showcase important new data on the risks seabed carbon stores face and how protective management can recover critical ecological processes that promote carbon capture and burial. It is becoming apparent that some of the most important and vulnerable places from a carbon storage perspective support economically important intensive fisheries. Such areas have also been neglected in the process of building marine protected area networks, because soft sediments have erroneously been considered of low biodiversity value and robust to human impacts. Managing ocean carbon stores to mitigate climate change is going to require an urgent rethink of management and protection priorities continental shelves.