SURFACE CHLOROPHYLL-A VARIATIONS ALONG THE SOUTHERN COAST OF JAVA DURING TWO CONTRASTING INDIAN OCEAN DIPOLE EVENTS: 2015 AND 2016

Abstract

Satellite-derived surface chlorophyll-a (chl-a) concentration off the southern coast of Java during the southeast monsoon season (July-September) of 2015 positive Indian Ocean Dipole (IOD) and 2016 negative IOD events was analyzed. The analysis was intended to examine how strong was the coastal upwelling, indicated by Ekman transport, during those two contrasting IOD events affecting the surface chl-a distribution. The results, however, did not reveal robust contrast patterns as was expected. Only weak coastal upwelling signals (offshore Ekman transport) were observed during the 2015 positive IOD event. This weak offshore Ekman transport combined with positive atmospheric flux prevented the exchange of cold thermocline water with the surface, resulting in weak SST cooling. The surface chl-a also only showed sporadic anomalous blooming during 2015. On the other hand, the 2016 negative IOD event has robust atmospheric and oceanic patterns. Strong onshore Ekman transport and distinct positive SST anomalies were observed. The surface chl-a patterns showing negative anomalies also clearly marked the oceanic response to those anomalously strong onshore Ekman transport. The results marked the important role of coastal upwelling for surface chl-a bloom in this area.