It has been widely known that the coastal upwelling along the southern coast of Java is generated by southeasterly wind which induces offshore Ekman Mass Transport (EMT) during southeast monsoon. However, the variability of EMT has not been fully described in previous studies. The present study investigated the variability of Ekman dynamics which consist of EMT and Ekman Pumping Velocity (EPV) along the southern coast of Java, based on remotely sensed data. We demonstrated the incongruity between the distribution of southeasterly wind speed and sea surface temperature (SST) during southeast monsoon which is related to the distribution of Ekman dynamics. Offshore EMT at the western region of the southern coast of Java is stronger than offshore EMT at the eastern region. However, stronger offshore EMT at the western part is inhibited by downwelling EPV while weaker offshore EMT at the eastern part is accelerated by upwelling EPV. Consequently, SSTs at the eastern parts are lower than those at the western parts. Thus, the changes of offshore EMT intensity from eastern to western parts are balanced by their EPV distributions which explain the incongruity between the distribution of wind speed and SST during southeast monsoon. On an interannual timescale, the combination of La Niña and negative Indian Ocean Dipole (IOD) events tends to weaken offshore EMT and EPV which reduce the intensity of Chl-a bloom and SST cooling during southeast monsoon season. Furthermore, ENSO has a less significant impact on the Ekman dynamics variability than IOD.

Blue carbon ecosystems in the Karimunjawa Islands may play a vital role in absorbing and storing the releasing carbon from the Java Sea. The present study investigated mangrove above-ground biomass (AGB) and carbon stock in the Karimunjawa-Kemujan Islands, the largest mangrove area in the Karimunjawa Islands. Taking the aerial photos from an Unmanned Aerial Vehicle combined with Global Navigation Satellite System (GNSS) measurements, we generated Digital Surface Model (DSM) and Digital Terrain Model (DTM) with high accuracy. We calculated mangrove canopy height by subtracting DSM from DTM and then converted it into Lorey’s height. The highest mangrove canopy is located along the coastline facing the sea, ranging from 8 m to 15 m. Stunted mangroves 1 m to 8 m in height are detected mainly in the inner areas. AGBs were calculated using an allometric equation destined for the Southeast and East Asia region. Above-ground carbon biomass is half of AGB. The AGB and carbon biomass of mangroves in the Karimunjawa-Kemujan Islands range from 8 Mg/ha to 328 Mg/ha, and from 4 MgC/ha to 164 MgC/ha, respectively. With a total area of 238.98 ha, the potential above-ground carbon stored in the study area is estimated as 16,555.46 Mg.

The Sulawesi Sea and the northern part of the Maluku Sea belong to the western equatorial Pacific that is influenced by the Mindanao Current. During the southeast (SE) monsoon, contrasting sea surface temperature (SST) distributions occur between these two seas. The purpose of this research is to investigate the mechanisms of contrasting SST distribution in the Sulawesi Sea and the northern part of the Maluku Sea under the condition of strong southerly wind during the SE monsoon season. Our analysis was based on satellite observations. Warmer (colder) SSTs are identified in the Sulawesi Sea (northern part of the Maluku Sea), which correspond to the weaker (stronger) southerly wind speed. Strong southerly winds in the northern part of the Maluku Sea generate eastward Ekman mass transport (EMT) that carries the water mass away from the coast, inducing upwelling. In contrast, the southerly winds from the Maluku Sea are blocked by the Gorontalo and North Sulawesi Mountains, creating low-wind areas in the Sulawesi Sea that are located on the lee side of those mountains. Furthermore, the existence of a valley between those mountains acts as a wind gap that channels the southerly wind to the Sulawesi Sea. Since the seaward EMT is weak and the latent heat release is not dominant, SSTs in front of the wind gap are only slightly reduced, possibly through the mechanisms of oceanic mixing.

Sea level rise is a pure impact of climate change. However, the process of studying sea level rise must include local factors that influence such as land subsidence. This study focuses on sea level rise using the CEEMDAN method and land subsidence using the DInSAR method. The location of this research is Pekalongan, Central Java, Indonesia. Tidal data used in this study was for five years, from 2016 to 2020, obtained from the Geospatial Information Agency (BIG). Then the data used to study land subsidence in this study uses Sentinel-1 Synthetic Aperture Radar (SAR) data in 2015, 2016, 2017, and 2020. Pekalongan is an area with mixed diurnal tidal types with Formzahl number 1.7. The sea level rise in Pekalongan is relatively high, at 10.6 mm/year. Then the land subsidence that occurred in Pekalongan is the phenomenon that has the most influence on the occurrence of coastal flooding in the region. The average land subsidence on the coast of Pekalongan is 5.37 cm/year. In addition, the sampling results in 6 areas showed that the most significant decrease was in Area 2, with a decrease of -7.91 cm/year. Based on this research, land subsidence is the most considerable influence on flooding in Pekalongan compared to sea level rise.