Performance prediction for Stommel’s perpetual salt fountain in the context of artificial ocean upwelling

Due to the typical temperature and salinity structure in wide parts of the global oceans, a self-sustaining, convective up or downflow within a vertical pipe can be established. This concept was introduced by Stommel et al. (1956) as the perpetual salt fountain. Recently, Stommel Upwelling Pipe (SUP) systems are gaining new interest as possible enabling technology for large-scale implementations of artificial upwelling of nutrient-rich deep ocean water to the ocean surface. This process is currently actively researched as part of several marine Carbon Dioxide Removal (CDR) approaches. Despite multiple studies conducted over the past decades, no method has yet been proposed to reliably predict performance and thus enable quantification of the potential of Stommel Upwelling Pipe (SUP) systems for artificial upwelling. In the present work, two performance prediction methods for SUP systems are introduced, one method based on the Reynolds-Averaged Navier–Stokes (RANS) equations and a one-dimensional method based on pipe flow equations. This twofold approach overcomes the limitations of previous studies and enables reliable performance estimation for a wide range of SUP setups. Both numerical methods are described in the present work, and their predictive capabilities are proven through rigorous verification, validation, and model intercomparison. The respective model assumptions are critically reviewed. Our results reveal key aspects of SUP performance and provide the basis for a reliable evaluation of the potential of SUP systems for artificial upwelling. Highlights: • Self-sustaining convection in vertical ocean pipes can drive artificial upwelling. • We introduce two new performance prediction methods for Stommel Upwelling Pipes. • Reliability is achieved through verification, validation, and model intercomparison. • We present new results for different device concepts and ocean conditions. • Our results reveal key aspects of Stommel Upwelling Pipe performance.