Waniek, Joanna J; Prien, Ralf D; Kolbe, Martin; Mairon, Tabea N L: Hydrographic data (temperature, salinity, dissolved oxygen, fluorescence, turbidity) collected by CTD during RV Sonne expedition SO305/2 in the Indian Ocean, July-August 2024 [dataset]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.995177 (dataset in review)

This dataset contains Conductivity-Temperature-Depth (CTD) measurements collected during the research expedition SO305-2 aboard the RV SONNE. The cruise took place in the Indian Ocean from July 21 to August 01, 2024, transiting from Singapore, across the Strait of Malacca, and into the open Indian Ocean before arriving in Port Louis, Mauritius. A total of 21 CTD casts were performed across 11 stations. These profiles were collected to investigate the distribution, sources, and element cycles of water masses in this region, and to help quantify anthropogenic stress and pollutant distribution extending from heavily populated coastal areas into the open ocean ecosystem. Continuous vertical profiles of physical and biogeochemical water properties were acquired using a Sea-Bird SBE 911plus CTD attached to a rosette water sampler equipped with 24 free-flow bottles (10 L each). The CTD was equipped with flushed dual sensors for temperature (SBE 3), conductivity (SBE 4), and dissolved oxygen (SBE 43). Additional instrumentation included a WET Labs ECO-FLNTURTD sensor for chlorophyll-a fluorescence and turbidity, a Biospherical QCP2350 PAR sensor (paired with a deck SPAR QSR2200 sensor for daylight referencing). Raw data acquisition and real-time visualisation were conducted using Sea-Bird Seasave software (V 7.23.2), with initial conversion and processing routines performed using SBE Data Processing software (V 7.23.2). All temperature, conductivity, and oxygen sensors were calibrated pre-cruise at the DAkkS-certified IOW calibration laboratory. To account for sensor drift and offset, field calibration water samples were collected for salinity and chlorophyll-a analysis; no field calibration was applied to the oxygen probes. This dataset includes the processed, quality-controlled downcast profiles for all 21 casts.