The Xiamen Symposium on Marine Environmental Sciences (XMAS 2027)

Diapycnal mixing near sloping seafloor plays a fundamental role in driving the upwelling of deep water masses in the global ocean. Previous modeling and observational studies have primarily focused on the sensitivity of this upwelling to near-bottom mixing, often attributed to internal wave breaking. However, the role of low-mode tidal forcing has received less attention. Here, we investigate the impact of tidal sloshing on diapycnal upwelling and tracer dispersion over sloping bathymetry. We show that, even when prescribed with identical mixing rates, models that exclude tidal sloshing produce substantially weaker diapycnal upwelling over steep slopes than models that explicitly include it, while differences remain small over gentle slopes. This difference arises from a kinematic coupling between spatial variations in mixing and the tidal displacement of water masses over the slope during each tidal cycle. Our results demonstrate that tidal sloshing exerts a fundamental dynamical control on deep-ocean upwelling that cannot be captured by mixing rates alone.  These findings provide guidance for representing deep-ocean upwelling in large-scale ocean models and for estimating water-mass transformation rates from observed diapycnal mixing and mean hydrography.