Freshwater Variability in the Southern Part of the Indonesian Maritime Continent During Indo-Pacific Climate Anomalies, Revealed by High-Resolution OGCM

Abstract

The Indonesian Maritime Continent (IMC) exhibits fresher conditions during the northwest monsoon, particularly in its southern hemisphere component (hereafter, “IMCsh”). The salinity budget formula is used to calculate the contributions of surface flux, river discharge, and advection to seasonal salinity patterns in the Banda Sea and its link to climatic events. The Banda Sea exhibits mild freshening in December and massive freshening in March. The December freshening is associated with surface flux caused by precipitation, and the March freshening with Java Sea zonal advection, with a modest contribution from surface flux. The Java Sea undergoes freshening during the early phase of the northwest monsoon, from November to December; this is dominated by surface flux, with a modest contribution from South China Sea (SCS) throughflow. This freshening is the major contributor to freshwater in the IMCsh. From January to May, Java Sea salinity declines, owing primarily to river discharge, with oceanic precipitation having slight effect. The contribution of low-salinity water from the SCS to the Java Sea is smaller than that of surface flux. Comparing years, IMCsh salinity is more closely associated with the Indian Ocean Dipole (IOD) and its current component with the El Niño-Southern Oscillation (ENSO). Freshening in the Banda Sea is strongly correlated with ENSO, while that in the Java Sea is highly correlated to the IOD. Salinization in the Banda Sea in September–November affects IOD in the following February. These findings reveal that the northwest monsoon freshening is driven primarily by river discharge and advection (independent or coupled).