Two distinct CO₂ sink/source characteristics are found in the tropical Indonesian seas from the compilation of observed data for the period 1984–2013. The western region persistently emits CO₂ to the atmosphere, whereas the eastern region is dynamic and acts either as a small source or sink of CO₂ to the atmosphere, depending on sites. The segregation is proximal to the Makassar Strait, which is located over the continental shelf and is one of the main routes of the Indonesian Throughflow (ITF). Lower salinity and higher silicate were found in the western region, suggesting a terrestrial influence in this area. Temperature has a limited influence in controlling different CO₂ sink/source characteristics in the west and east. However, an SST change of −2.0°C during La Niña events effectively reduces the pCO₂ difference between the atmosphere and surface seawater by 50% compared to normal year conditions. During La Niña events, higher wind speeds double the CO₂ flux from the ocean to the atmosphere compared to that of a normal year. In the continental shelf area where the CO₂ sink area was found, data of over 29 years show that the seawater pCO₂ increased by 0.6–3.8 μatm yr⁻¹. Overall, the seawater pCO₂ of the Indonesian seas is supersaturated relative to the atmosphere by 15.9 ± 8.6 μatm and thus acts as a source of CO₂ to the atmosphere.

The baroclinic tides in the Red Sea are simulated using a three‐dimensional, nonhydrostatic, high‐resolution Massachusetts Institute of Technology general circulation model. Various observations have been used to validate the simulation results. A good match between the model results and observations from five tidal gauges has been obtained. Tidal amplitude and phase data from 21 tidal stations present high correlation coefficients and low deviations with the model results. Comparisons between model and Oregon State University Tidal Inversion Software data suggest consistent results, with only small discrepancies at the locations of the amphidromic points. Tidal currents from four mooring observations are in good agreement with the simulation results, with discrepancies appearing in shallow areas and those with complex bottom topography. Based on the simulation results, the basic characteristics of baroclinic tides in the Red Sea are analyzed. The properties of barotropic tides, and distribution of the forcing function parameter, indicate that the baroclinic tides are generated mainly in four areas: the Bab‐el‐Mandeb (BAM) Strait, the southern Red Sea, the Gulf of Suez, and the Strait of Tiran. This is confirmed by the spatial distributions of baroclinic tidal kinetic energy and energy flux. The properties of the conversion rate from barotropic tides to baroclinic tides, and the divergence of baroclinic energy flux, further reveal quantitatively that the southern Red Sea features the most of the generated baroclinic energy. The majority of the baroclinic energy disappears within the four areas, either dissipating due to friction and bottom drag or converting back to barotropic energy.

[1] A 1/36° high‐resolution nested structure ocean model for Indonesian seas that combines atmospheric and tidal forcings (hereafter referred to as IP3‐tide) has been developed based on the modified Princeton Ocean Model (POM). Prior to model application, in 2004, we analyzed the IP3‐tide by using observational data, derived data, and a global atlas model. A comparison between IP3‐tide with 13 tide gauge points and 11 T/P points resulted in 76–92% certainty. Correlation of temperature from scattered depths and points between the model and XBT data reached 97.5% agreement. The modeled velocity successfully captured the low and high frequency variability shown in INSTANT mooring and TAO/TRITON data. Explicit simulation of tidal processes by regional ocean circulation model improved the representation of circulation in the Indonesian seas. At the tidal frequencies, vertical mixing is increased due to the impact of baroclinic tides and horizontal mixing is enhanced by presence of barotropic tidal motion. Enhanced mixing is responsible for eroding the salinity maximum found in the water masses advected from the Pacific Ocean. On the other hand, seasonal variability changes the vertical density structure of water column, which influences the distribution of internal tidal waves. These results demonstrated the importance of explicit tide simulation by regional ocean circulation model for correct presentation of ocean circulation structure and its variability in the Indonesian seas.