Tracer distributions in ocean models with lateral and isopycnal diffusion

Abstract

The time dependent tracer evolution simulated by 1- and 3-dimensional ocean models is examined. The former model resolves only vertical diffusion with a constant vertical diffusivity, while the latter is a primitive equation ocean circulation model which resolves the momentum, temperature, salinity and mass balance in an idealized North Atlantic basin scale box domain. The tracer distributions over 100 years of simulated time in the 3-dimensional model are obtained for both lateral and isopycnal diffusive parameterizations. The basin averaged tracer distribution is used to calibrate the 1-dimensional model. Time varying tracer distributions from the 3-dimensional model, averaged over zonal, meridional and sector sections through the core of the gyral circulation, are then fitted to the 1-dimensional model. The results show that isopycnal diffusion leads to a more intense tracer front in the thermocline regions compared to lateral diffusion during the transient evolution. The front in both cases are stronger than that predicted by the 1-dimensional model. This is due to horizontal processes importing the tracer locally. The long term asymptotic results are well simulated by the 1-dimensional model. Implications for global carbon cycle and energy balance climate ocean models are considered.