Effect of tides on the circulation and hydrography in the Indonesian Seas: Comparison of a model with and without tidal forcing

The Indonesian seas are located at the interface between the Pacific and the Indian Oceans, acting as a main pathway of water exchange between these basins. The Indonesian seas also host a rich and diverse marine environment. Understanding the mechanisms that control local circulation and hydrography, and how they may respond to climate change is hence of direct interest for both the global climate and the welfare of the marine ecosystem. Here, we investigate the effect of the interaction between the Indonesian seas’ complex topography and large tidal currents on the regional circulation and water mass transformation using a realistic regional ocean model. Our Model is based on NEMO and the ORCA 1/12-degree configuration but employs a hybrid constant depth-terrain following coordinate system (z-sigma) in the vertical to allow for a good representation of both the mixed layer and shallow coastal regions and is forced by 34 tidal constituents. Sensitivity experiments with tidal forcing switched on and off are conducted to isolate the effect of tides and their interaction with topography in: i) generating internal waves and promoting mixing and water transformation, ii) generating residual currents through tidal rectification that influence the regional flow patterns and iii) altering the intensity of the Indonesian throughflow. Comparison with available observations (e.g., tidal gauges and satellites) is also used to test the realism of the model and verify our inferences from the model simulations. This study is part of a large-scale effort for Addressing Challenges of Coastal Communities through Ocean Research for Developing Economies (ACCORD project).