Stochastic Transport in Upper Ocean Dynamics III. STUOD 2023 Workshop, Plouzané, France, September 25–28

This volume contains the Proceedings of the 4th Stochastic Transport in Upper Ocean Dynamics Annual Workshop held on 25–28 September 2023.Thework-shop is a core part of the Stochastic Transport in Upper Ocean Dynamics (STUOD) project, which is supported by a European Research Council (ERC) Synergy Grant and is led by four Principal Investigators that bring together three world-class institutions: Prof. Bertrand Chapron, French Research Institute for Exploitation of the SEA (IFREMER), Prof. Dan Crisan, Imperial College London (ICL), Prof. Darryl D. Holm, Imperial College London (ICL) and Prof. Etienne Mémin, National Institute for Research in Digital Science and Technology (INRIA). The project aims to deliver new capabilities for assessing variability and uncer-tainty in upper ocean dynamics and provide decision makers a means of quantifying the effects of local patterns of sea level rise, heat uptake, carbon storage and change of oxygen content and pH in the ocean. The project will make use of multimodal data and will enhance the scientific understanding of marine debris transport, tracking of oil spills and accumulation of plastic in the sea. As in previous years, the 4th STUOD Annual Workshop 2023 focused on a range of fundamental topic areas, including: 1. Observations at high resolution of upper ocean properties such as temperature, salinity, topography, wind, waves and velocity 2. Large-scale numerical simulations 3. Data-based stochastic equations for upper ocean dynamics that quantify simula-tion errors 4. Stochastic data assimilation to reduce uncertainty Each chapter in the present volume illustrates one or several of these topic areas. Many chapters offer new mathematical frameworks that are intended to enhance future research in the STUOD project. The workshop was held in the hybrid mode and brought together early-career academics, postgraduate students, senior members of the community and other invited guests from across the world that included the UK, France, Netherlands, Italy, Germany and the USA.