Study On The Bottom Drag Dissipation In The Deep Ocean And The Effect Of Diapycnal Mixing

The global dissipation caused by bottom boundary layer drag is one of the major pathways for the consumption of kinetic energy in the deep ocean.However,the spatial distribution and global integral of the drag dissipation are still debatable.This paper presents an updated estimate of the dissipation rate,using the barotropic component of surface geostrophic currents and 632 in situ velocity measurements.Also,the seafloor roughness is proposed as a parameter of drag efficiency in the parameterized method.The results provide a map of the drag dissipation rate with a global integral of 0.26 TW.Approximately 66% of this dissipation occurs in the Southern Ocean,which is consistent with the proportion of wind power input into this region.Building upon the work in previous studies on the bottom boundary layer drag,more long-period observations are used,eliminating the influence of the baroclinic contribution to the surface geostrophic currents in the construction of the bottom velocity,and taking topographic roughness into account.The estimates have implications for the maintenance of density structure in the deep ocean and understanding of the deep sea kinetic energy budget.The global diapycnal transport in the ocean interior is one of the significant branches to return the deep water back toward near-surface.However,the amount of the diapycnal transport and the seasonal variations are not determined yet.This paper estimates the dissipation rate and the associated diapycnal transports at 500 m,750 m and 1000 m depth throughout the global ocean from the wide-spread Argo profiles,using the finescale parameterizations and classic advection-diffusion balance.The net upwelling is ~5.2±0.81 Sv(Sverdrup)which is approximately one fifth in magnitude of the formation of the deep water.The Southern Ocean is the major region with the upward diapycnal transport,while the downwelling emerges mainly in the northern North Atlantic.The upwelling in the Southern Ocean accounts for over 50% of the amount of the global summation.The seasonal cycle is obvious at 500 m and vanishes with depth,indicating the energy source at surface.The enhancement of diapycnal transport occurs at 1000 m in the Southern Ocean,which is pertinent with the internal wave generation due to the interaction between the robust deep-reaching flows and the rough topography.Our estimates of the diapycnal transport in the ocean interior have implications for the closure of the oceanic energy budget and the understanding of global Meridional Overturning Circulation.