Remote energy sources for mixing in the Indonesian Seas.

The role of the Indonesian Seas in climate is attributed to the intense mixing observed throughout the region. Mixing cools the surface temperature and hence modifies the atmospheric convection centered over the region. Mixing also controls the heat exchange between the Pacific and Indian Oceans by transforming water-mass properties while they transit through the region. Mixing in the Indonesian Seas has long been identified to be driven locally by tides. Here we show that the observed mixing can also be powered by the remotely generated planetary waves and eddies. We use a regional ocean model to show that the Indonesian Seas are a sink of the energy generated in the Indian and Pacific Oceans. We estimate that 1.7 GW of the remotely generated energy enters the region across all straits. The energy flux is surface intensified and characterized by a convergence, implying dissipation and mixing, within the straits and along topography. Locally, energy convergence associated with this process is comparable in magnitude to tidal energy dissipation, which dominates the deep ocean.

Dissipation of mesoscale eddies and its contribution to mixing in the northern South China Sea.

It is reported that turbulent mixing is enhanced in the South China Sea (SCS), and it is highly variable in both space and time. Generation and breaking of internal tides has been identified as the main process to drive turbulent mixing in the SCS, while the contributions from other processes are not clear enough. Here we investigate the potential contribution from mesoscale eddies to turbulent mixing in the SCS using a high resolution numerical simulation. Our results show that mesoscale eddies in the SCS effectively dissipate over complex rough topography and indicate that the generation of submesoscale motions and lee waves are two pathways for the transfer of mesoscale eddy energy down to small dissipation scales. The energy loss from mesoscale eddies near the Xisha Islands is estimated to be sufficient to sustain turbulent kinetic energy dissipation rate of O (10-8) W/kg. This study suggests an alternative and potentially efficient mechanism to internal tides for the local maintenance of turbulent mixing in the SCS.