Spatiotemporal Patterns and Environmental Drivers of Particulate Inorganic Carbon (PIC) Variability in the Southern Waters of Sumatra‐Java Islands.

The southern waters of the Sumatra‐Java Islands, within the Indo‐Pacific Warm Pool, are highly susceptible to global climate change impacts. Understanding particulate inorganic carbon (PIC) dynamics and environmental responses in this region is critical for assessing climate change effects on marine ecosystems. Utilizing two decades of remote sensing PIC data (2003–2022), we identified five sub‐regions via K‐means clustering: the Sunda Strait, southern coastal/offshore waters of Sumatra Island, and southern coastal/offshore waters of Java Island. Self‐Organizing Map explored interannual PIC variations, while Generalized Additive Models delineated driving factors. In the Sunda Strait, PIC dynamics are influenced by water exchanges between the Indonesian Seas (ISs) and eastern Indian Ocean (EIO). Seasonally, PIC concentrations peak during the east monsoon (boreal summer); decreasing during positive Indian Ocean Dipole (+IOD) and El Niño events. Along the southern Sumatra, PIC variations positively correlate with rainfall and photosynthetically active radiation (PAR). Along the southern Sumatra, upwelling drives PIC variations, with higher concentrations during mature summer monsoon induced upwelling periods. PIC increases during +IOD and decreases during El Niño. Our study highlights the nexus between nutrients, physical factors (e.g., rainfall), and climatic events (e.g., El Niño) on PIC concentrations. Climate‐induced changes in oceanic physical processes modulate nutrient concentrations, thereby governing PIC variations. We propose a mechanistic model to elucidate PIC variations in upwelling areas. Findings suggest that prospective climate variability, encompassing alterations in climate events, rainfall, and temperature, may escalate PIC concentrations within the study area, advocating PIC as a forward‐looking climate change indicator. Plain Language Summary: Understanding the response of particulate inorganic carbon (PIC)—a primary form of oceanic carbon ‐ to environmental changes in the vulnerable southern waters of the Sumatra‐Java Islands is crucial for assessing the marine ecosystem. We used satellite image data to examine the variability of PIC, from 2003 to 2022. Our research showed that PIC concentrations varied across the area. In the Sunda Strait, a narrow body of water between land masses, water movement between the Indonesian Seas and eastern Indian Ocean influences PIC concentrations. In the southern waters of Sumatra Island, we discovered that increased rainfall and sunlight contribute to higher PIC concentrations. In the southern waters of Java Island, upwelling, an ocean physical process that brings nutrient‐rich water to the surface, plays a significant role. Our study delineates the interplay between nutrients, physical factors (e.g., rainfall), and climatic events (e.g., El Niño) on coccolithophore biomass. Climate changes drive alterations in oceanic physical processes, which in turn affect nutrient availability, thereby governing the growth of coccolithophores. Findings suggest prospective climate variability, inclusive of alterations in climate events, rainfall, and temperature, may escalate PIC concentrations within the study area, advocating PIC concentrations alterations as a forward‐looking climate change indicator. Key Points: Climate alters oceanic physical processes, thereby modulating nutrient availability, which in turn directly governs Particulate Inorganic Carbon (PIC) variationsA 20‐year analysis identified three core mechanisms driving PIC spatiotemporal variations in the study areaRising PIC under future climates predicts higher carbon sedimentation rates, marking PIC as a key climate indicator [ABSTRACT FROM AUTHOR]