Tidal Mixing Estimation in the Indonesian Seas and Its Effects on Water Mass and Circulations

Using a three-dimensional numerical model MITgcm, this paper estimated the tide-induced dissipation and mixing based on the energy budget method and explored its influence on water mass characteristics of Indonesian Seas, ITF transport and the heat transport into Indian Ocean. Results showed that the normalized amplitude of internal tides maximizes in the Indonesian Seas with values of about 20~40m. The Sangihe Sill, Seram Sea and Ombai Strait are three major sites of internal tide generation, where the depth-integrated baroclinic energy flux reaches 40 kW·m^-1. The internal tide energy in the Sulu Sea is mainly generated from the conversion of local barotropic tides, whereas that in the Sulawesi Sea and Banda Sea is from remotely generated internal tides. Intense tide-induced turbulence occurs in most areas of the Indonesian Seas with estimated dissipation rate of over O (10^-9~10^-8) W·kg^-1 and mean diapycnal mixing of over O (10^-4) m²·s^-1. In the intense mixing area such as Halmahera Sea, the dissipation rate exceeds O (10^-7) W·kg^-1 and diapycnal mixing exceeds O (10^-2~10^-1) m²·s^-1. The estimated diapycnal mixing by energy analysis method is one or two order of magnitudes larger than direct estimation by using topography roughness and buoyant frequency. For the water mass characteristics, tidal mixing makes the subsurface water warmer and fresher, the middle water warmer and saltier, and the deep water warmer and fresher, resulting in a more vertically uniform water mass. For the circulation characteristics, tidal mixing leads to a more reasonable distribution rate of the western and eastern route of ITF; Meanwhile, tidal mixing is very important to the simulation of deep circulation in the Lifamatola Strait and it could modify the vertical profile of ITF in the exit. For the ocean heat content (OHC) of the Indonesian Seas, tidal mixing decreases the OHC in the surface water whereas increases it in the deep water, leading to an increase of about 0.03PW of the total heat transport into Indian Ocean by modifying the vertical profiles and water temperature in the exit of ITF.