The marine ecosystem is a highly complex and continually shifting organism that plays significant importance in the biogeochemical cycles of the Earth and provides essential support for a wide range of ecological and socioeconomic processes [Refulio-Coronado et al., 2021; Saunders et al., 2017). The chlorophyll-a concentration is a significant parameter among the several indicators used to assess the health of marine environment (Franklin et al., 2020; Park et al., 2015). This resource provides significant insights into primary productivity and phytoplankton biomass. Phytoplankton, being the fundamental constituents of marine food webs, have a significant influence on the trophic organisation and carbon dynamics within oceanic ecosystems. Therefore, it is important to have a comprehensive understanding of the geographical and temporal patterns in the distribution of chlorophyll-a in order to acquire useful insights on the dynamics of the marine environment. (Lu et al., 2021; Bierman, et al., 2011).
The Indonesian seas play an essential role in the climate system and influences interactions between oceans on a global scale. The Indonesian Through Flow (ITF), the flow of water from the Pacific Ocean to the Indian Ocean through Indonesian waters mixed with regional water masses, makes the water conditions in Indonesia unique (Gordon, 2005). Indonesia has marine areas with abundant marine resources. Indonesia's marine biodiversity is supported by the fertile waters of Indonesia, which are certainly rich in phytoplankton. The Indonesian region is subject to the impact of the Asian monsoon, particularly the Northwest Monsoon (NWM) from October to April, and the Australian monsoon, known as the Southeast Monsoon (SEM), from April to October. These monsoons follow an annual cycle (Hermawan, 2015). These monsoon phenomena cause changes in the direction of water masses in some areas of Indonesian waters that affect chlorophyll-a concentrations. The upwelling phenomenon occurs during the SEM, and the downwelling phenomenon occurs during the NWM (Gordon, 2005).
The Indonesian Seas, which includes a wide range of waterways, islands, and straits, is distinguished by its notable marine biodiversity and substantial oceanographic complexity. The geographical area in question plays a crucial role as an essential link between the Pacific and Indian Oceans (Sprintall and Révelard, A, 2014). It is home to a wide array of ecosystems, encompassing various habitats such as coral reefs and deep-sea trenches. The complex interaction between ocean currents, upwelling phenomena, inputs from waterways and local physicochemical circumstances results in a diverse pattern of chlorophyll-a dynamics (Nazeer, et al., 2016).
The Eastern Indonesian seas region, as shown at Fig. 1, are widely acknowledged as being among the most biodiverse marine ecosystems on a worldwide scale (Gonzales, A T et al., 2019; Padilla J E & Hudson A et al., 2019). Changes in chlorophyll-a concentration have a direct effect on primary productivity, which has big effects on how the food web works and how ecosystems change over time (Zhang K. et al., 2023). Understanding the subtleties of the distinctive biodiversity in this area requires a comprehensive knowledge of the variations of chlorophyll-a.
Numerous factors influence the variation of chlorophyll-a throughout the Indonesian Seas Region. Physical forces, such as monsoon winds, ocean currents, and coastal upwelling, can have a substantial effect on nutrient transport and mixing, and thus on phytoplankton growth [Ningsih et al., 2013; Yu et al., 2019, Mandal, et al., 2022]. These activities have a large impact on the distribution of nutrients and plankton, which affects chlorophyll-a levels. Insights into the linked oceanographic mechanisms that control nutrient transport, mixing, and ecosystem dynamics can be gained by studying the spatial-temporal variability of chlorophyll-a in this region. Additionally, anthropogenic inputs, such as nutrient discharges from land-based activities, further confound chlorophyll-a's spatial distribution. Climate change and ocean warming can alter stratification patterns, which in turn influences nutrient availability and phytoplankton blooms (Asch, et al., 2019).
The monitoring of the concentration of chlorophyll contributes significantly to the comprehension of the ocean's health. This study delivers valuable insights into the accessibility of nutrients and the overall condition of the marine ecosystem. The Sentinel-3 Ocean and Land Color Instrument (OLCI) provides frequent and comprehensive worldwide coverage of ocean color data at a high resolution.
High spatial and temporal resolution makes it possible to look at chlorophyll levels in the world's oceans on a regular basis and in large amounts. The primary aim of this study is to examine the influence of monsoon activity on the variation of chlorophyll distribution in the seas of the eastern Indonesian region. This investigation will be conducted utilizing data from the Sentinel-3 Ocean and Land Color Instrument (OLCI).
Study Area
This study emphasizes the spatio-temporal variability of chlorophyll-a around the Eastern Indonesian Seas Region, which range between 11°S and 8°N latitude and 115°E and 145°E longitude. The boundaries of the region encompass a region extending from the western Pacific Ocean to the eastern Indian Ocean. The seas included in the publication "Limit of Oceans and Seas" by the International Hydrographic Organisation (IHO) in 1953 include the Banda Sea, Flores Sea, Sulawesi Sea, Maluku Sea, Seram Sea, Halmahera Sea, Timor Sea, Arafura Sea, and Savu Sea (IHO, 1953). (shown at Fig. 1).