Program

It is generally known that the Indonesian Seas (IS) plays an important role in the global thermohaline circulation through the Indonesian Throughflow. However, little is known about the marine chemistry of the IS. Here, we present a high-resolution water column dataset of the carbonate system collected during a cruise to the western Indonesian Seas in the southeast monsoon season of June 2015. The study area covered the Karimata Strait, west part of the Java Sea and the Sunda Strait. In the Karimata Strait, a river plume characterized by low salinity (~ 31.3), dissolved inorganic carbon (DIC, ~ 1814 µmol kg-1) and total alkalinity (TAlk, ~ 2066 µmol kg-1) due to the Kapuas River input from the Kalimantan/Borneo was observed. In the western Java Sea waters were well mixed as because of the shallow water depth and strong zonal monsoon wind, leading to homogenous distributions of both salinity (the average ~ 32.7) and the carbonate system parameters (DIC = 1857 - 1882 µmol kg-1; TAlk = 2144 - 2183 µmol kg-1). In the Sunda Strait, water from the Indian Ocean intruded and mixed with the Java Sea water resulting dilution of salinity and DIC (1877 - 2298 µmol kg-1) and TAlk (2107 - 2366 µmol kg-1). The distribution of pCO2 showed their different variability among study regime which influenced by river plume, water well mixed and water exchange were ranged 382 - 469µatm, 357 - 438µatm, and 393 - 974 µatm, respectively. A two end member mixing model was constructed in both the Karimata Strait-west part of Java Sea and the Sunda Strait to distinguish the effects of water mass mixing and biological alteration on the carbonate system. Physical processes dominated the carbonate system dynamics in both areas. In the region influenced by the Kapuas River near the Karimata Strait and west part of Java Sea, however, the biological production was observable as revealed by a net removal of DIC. In the Sunda Strait, the South Java Current brought waters enriched with nutrients stimulating the biological consumption of DIC. Taken together, the significant spatial variations of the carbonate system in the Western Indonesian Seas were controlled by the combination of physical mixing and biological activities. This study revealed a better insight about carbonate system dynamics in tropical areas.