Seasonal variation of chlorophyll-a in South Java over the past quarter-century

A comprehensive investigation was conducted to examine the variations in Chlorophyll-a (Chl-a) levels in the waters located to the south of Java Island throughout the past quarter-century. This study employs satellite data and reanalysis data gathered from multiple sources spanning the period between September 1997 and December 2022. The application of EOF analysis revealed that the most notable elevation in Chl-a contents took place during the seasons of SON (September, October, November) and DJF (December, January, February) in the years 1997/1998 and 2006/2007. It has been determined that this significant increase in Chl-a content in southern Java is contingent upon the fulfillment of a number of circumstances. These conditions are associated with climatic patterns in the Indian Ocean and Pacific Ocean. An elevation in Chl-a content was seen throughout the months of SON and DJF in instances where the Indian Ocean Dipole (IOD) had a positive phase. The concurrent occurrence of a powerful positive IOD and El Niño event in the Pacific Ocean is highly probable to result in a substantial elevation in Chl-a content in the southern region of Java. In addition, our findings indicate that the phenomenon of Kelvin wave upwelling significantly contributes to the elevation of Chl-a levels during the months of June, July, August (JJA), and SON.