Deep ocean mixing mismatch between model and observational estimates

Abstract

The vertical diffusivity in the ocean is known to vary widely across the global ocean, and understanding this variation is essential for simulating water mass transformation and global ocean circulation. Here, we propose an approach combining a global ocean circulation model with a steady-state tracer model to estimate the global distribution of vertical diffusivity, including in the deep ocean. This method reveals very small values in most regions of the upper ocean and patchy high values in localized areas, as well as higher values in the deeper ocean. These results highlight the necessity of larger mixing coefficients than those suggested by observational estimates in the deep ocean to realistically reproduce observed temperature and salinity distributions in models. This discrepancy regarding the deep ocean mixing warrants further investigation through both model and observational studies.