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The Gulf of Madura is heavily utilized for shipping, fishing, and oil exploration. These activities impact the marine environment. This study aims to describe the spatial and temporal variability in oceanographic parameters, vertical current structures, trends, and ocean health conditions based on oceanographic parameters estimated from the OHI value. The data used in this research consists of INDESO and Marine Copernicus data. The results of the study show that monsoon phenomena greatly influence temperature and salinity in the Gulf of Madura, with temperature increasing and salinity decreasing during the northwest monsoon, and vice versa during the southeast monsoon. An analysis of oceanographic variables over the past 12 years showed an increase in salinity and nitrate variables, and a decrease in other variables. The trend fluctuation is still within the quality standard for seawater according to government regulation number 22 of 2021. The results of the calculation of the ocean health index show that the Gulf of Madura is in a fair condition with a value of 0.63. This finding can be used to manage and utilize marine space sustainably without deteriorating the ocean’s health.

As part of the Indonesian Throughflow (ITF) from western route, water masses in the Bali Sea are fed by North Pacific water masses. We examined the mixing strength in the Bali Sea which contributes to reducing the core layer S-max of the North Pacific Subtropical Water (NPSW) from 34. 8 – 35 psu in the source region to 34.5 psu in the Bali Sea. Using Thorpe method, we found the mixing strength in the Bali Sea is relatively low. The turbulent kinetic energy dissipation rate (ɛ) of O( 10-11 - 10-6 ) WKg-1 and density turbulent diffusivity (Kρ) are O (10-5 10-3) m-2s-1 were similar to typical open ocean values. However, mixing in the eastern region of the Bali Sea is relatively stronger than in the western region. Based on the critical Ri #, we found the Thorpe scale (LT) under Ri# < 0.25 in the eastern region, which is contrary to other parts. It indicated the turbulent mixing was dominantly caused by shear instability. Shear from the strong outflow of ITF towards the Lombok Strait and the reversal northward current in the lower layer forces a strong turbulent layer.

The Indian Ocean Dipole (IOD) may affect the distribution pattern of the sea surface temperature (SST) in the Indonesian seas. Understanding this impact is crucial for comprehending the dynamics of marine ecosystems, particularly in Lampung Bay. This study evaluates IOD effects on SST and associated upwelling/downwelling in Lampung Bay. 2014 fish catch data analysis reveals during negative IOD phases, SST increases (0.2°C to 2°C) with subsequent downwelling, coinciding with reduced catches (609.18 tons vs. 3,079 tons normal). Conversely, positive IOD phases show SST anomalies (-1°C to -2.5°C) with upwelling, correlating with increased catches to 3,349 tons in 2018. IOD-SST relationship primarily observed in Lampung Bay’s open connection to Sunda Strait (r=0.64 to 0.69), while weak correlations in coastal waters (r < 0.2) suggesting the influence of other factors on SST in Lampung Bay.

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The eastward propagation of atmospheric waves along the equatorial band from the central equatorial Indian Ocean to the western Pacific Ocean passing through the Indonesian Maritime Continent (IMC), known as the intraseasonal Madden Julian Oscillation (MJO) event, plays an important role on modulating both atmospheric and upper ocean dynamics along its path. This study aims to investigate the MJO active phase dynamics and its impact on changes in near-surface seawater temperature and mixed layer depth (MLD) anomaly in the Banda Sea Indonesia, using multi-datasets of atmospheric reanalysis, satellites derived sea surface temperature (SST), and Argo float between 2017 - 2018. This study revealed that the MJO waves propagate eastward along the southern equator-line over the IMC and pass through the Banda Sea, associated with significant decreased on Outgoing Longwave Radiation (OLR) and increased in zonal wind speed at 850hPa. The study result shows anomalous increased on surface wind speed and SST cooling during of MJO active phase. The amplitude peaks of filtered ocean-atmosphere variables range between 30 - 60 days. Argo float datasets in the Banda Sea for the first time captured upper ocean responses to the arrival of the MJO active phase, as characterized by a negative temperature anomaly of ~0.3°C in the surface mixed layer, large temperature anomaly of ~0.8°C in the thermocline layer and the deepening of the MLD of ~25 m. Hence, the MJO active phase impacts significantly on surface and vertical temperature cooling and regulate upper ocean mixing intensity in the Banda Sea. [ABSTRACT FROM AUTHOR]