CO₂ sink/source characteristics in the tropical Indonesian seas

Two distinct CO 2 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 CO 2 to the atmosphere, whereas the eastern region is dynamic and acts either as a small source or sink of CO 2 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 CO 2 sink/source characteristics in the west and east. However, an SST change of −2.0°C during La Niña events effectively reduces the pCO 2 difference between the atmosphere and surface seawater by 50% compared to normal year conditions. During La Niña events, higher wind speeds double the CO 2 flux from the ocean to the atmosphere compared to that of a normal year. In the continental shelf area where the CO 2 sink area was found, data of over 29 years show that the seawater pCO 2 increased by 0.6–3.8 μatm yr −1 . Overall, the seawater pCO 2 of the Indonesian seas is supersaturated relative to the atmosphere by 15.9 ± 8.6 μatm and thus acts as a source of CO 2 to the atmosphere.