Spatiotemporal variability in particulate organic carbon in the southern coastal waters of Java Island and its major controlling factors

The southern coast of Java Island is characterized by a typical upwelling system in the Indo-Pacific warm pool, yet the dynamics of particulate organic carbon (POC) and its driving processes remain poorly understood. This study investigated the spatiotemporal variability of surface POC along the southern coast of Java from 2003 to 2022 using satellite observations, physical and biogeochemical variables, and EOF/SOM analyses to elucidate the controlling mechanisms at multiple timescales. Seasonally, POC peaks during the southeast monsoon due to enhanced nutrient supply from coastal upwelling, but declines during the northwest monsoon as northwesterly winds weaken upwelling, thereby reducing nutrient availability and limiting phytoplankton growth. On interannual timescales, the Indian Ocean Dipole (IOD) exerts a stronger and more direct influence on POC variability than the El Niño–Southern Oscillation (ENSO). POC concentrations generally increase during + IOD/El Niño events and decrease during –IOD/La Niña events primarily in response to variability in upwelling-related conditions, including SST, SLA, EMT and EPV. Notably, the 2009 El Niño Modoki induced negative POC anomalies through atmospheric teleconnections that enhanced sea surface warming and ocean stratification while suppressing upwelling. The 2011–2012 multiyear La Niña may have contributed to anomalously wet conditions over Indonesia in 2013. These conditions were associated with extreme precipitation in 2013, which suppressed upwelling and reduced POC. These findings demonstrate that both the diversity of climate events and their remote influences critically shape carbon dynamics in tropical upwelling systems, with important implications for understanding ecosystem responses and carbon cycling under a warming climate.