Seasonal and interannual variations of surface salinity in the Java Sea during 1982-2002 derived from coral data

The Indonesian seas play an important role in modulating the Indonesian throughflow (ITF), which may affect on variations of the El Nino/Southern Oscillation (ENSO) and Asian monsoon. It is also suggested that significant ITF variability is linked to changes in the freshwater budget of the western Indonesian seas and Southeast Asian monsoon winds. In this study, chemical components, such as d18O, Sr/Ca and Ba/Ca, were measured for the period 1982 - 2002 with monthly resolution in the coral skeleton (Porites sp.) collected from the Java Sea. Then, we estimated the variation of d18O of seawater, which is directly related to salinity, using d18O and Sr/Ca data in the coral. Our salinity data showed freshening occurred during the northwest monsoon (austral summer) probably due to heavy precipitation in Southeast Asia and eastward zonal wind. In addition, Ba/Ca ratios showed clear seasonality from 1982 to 1994 with maximum during the southeast monsoon (austral winter). However, after the 1993/94 Indian Ocean Dipole (IOD) event, seasonality of Ba/Ca has been obscured. Anomalous variations in seawater d18O were also observed during the 1993/94 IOD besides the 1997/98 ENSO events. Coral data from the Java Sea do not represent local precipitation rate, but seem to reflect variations of water masses around the Indonesian seas.