Two Centuries of Oceanographic Data in the Indonesian Seas and Surroundings: Historical Trends, Gaps, and Future Challenges

Abstract. The Indonesian Seas and Surroundings (ISS) play an important role in global ocean circulation by connecting the Pacific and Indian Oceans via the global thermohaline circulation. This region regulates the exchange of water mass, heat, salinity, and biogeochemical elements, further influencing the global climate and carbon cycle. Consequently, extensive observations and surveys, particularly the in-situ measurements, have been conducted over the past two centuries. This study analyzed over 461,865 oceanographic casts from multiple international repositories, with 360,409 casts, or 21.97 % rejection, after rigorous quality control. The findings indicate that data collection was sparse and temporally limited before the early 19th century, with a marked increase beginning from the mid-20th century. Spatially, observations are heavily concentrated along major international shipping routes, including the Makassar Strait, Malacca Strait, and South China Seas, while vast areas, such as the Halmahera Sea, Timor Sea, Java Sea, and Sulawesi Sea, remain poorly detected. Temperature and salinity are the most collected data, whereas deep-sea observations, particularly below 800 meters, are critically lacking, with limited measurements of essential ocean variables such as dissolved oxygen, nutrients, and currents. Additionally, coastal regions exhibit substantial data deficiencies. Given the region's complex ocean-atmosphere interactions and unique topographic features, the current observational coverage remains insufficient to resolve the uncertainties in Indonesian Throughflow (ITF) variability, ocean heat transport, and monsoon forecasting. This study proposes to address the gaps by deploying autonomous monitoring technologies (Argo floats, gliders, moored buoys) in deep-sea and coastal regions, expanding regional observational networks, and enhancing executable data-sharing mechanisms. The raw datasets can be accessed freely from the website provided in the text, and processed datasets are preserved in data repositories with a corresponding assigned DOI. Final datasets and the computed cast per half-degree grid square with Python syntax are freely available from the Mendeley repository. The data were in the TXT file format, and we used Ocean Data View Software (ODV Ver. 5.7.2), Python, and QGIS Software to process, visualize, and analyze the data.