A consistent regional dataset of dissolved oxygen in the western Mediterranean Sea (2004–2023): CTD-O ₂ WMED

Abstract. The Mediterranean Sea is experiencing rapid environmental changes, underscoring the urgent need for high-quality, long-term datasets to quantify trends and assess impacts on biogeochemical cycles. Over the past few years, a lot of work has been done to improve and ensure data quality in the western Mediterranean Sea (WMED), but reliable dissolved oxygen (O2) data remain scarce. This is a critical gap as oxygen is a key indicator of marine ecosystem health and plays a central role in carbon and nutrient cycling. To address this gap, we compiled and rigorously quality-controlled a new regional-scale WMED dataset of O2 data from sensors mounted on conductivity, temperature, and depth (CTD) probes: CTD-O2WMED. This product includes over 1000 previously unpublished high-resolution vertical profiles of CTD-O2 measurements mostly collected within Italian cruises between 2004 and 2023. The quality control (QC) process involved sensor post-calibration against discrete Winkler measurements, primary screening, and a secondary check based on crossover analysis with reference datasets. Combined, this ensures the consistency of the final corrected CTD-O2WMED across both space and time. CTD-O2WMED provides a robust observational foundation for assessing trends of dissolved oxygen variability, mainly associated with climate change, anomalies related to deoxygenation processes, and contributes to advancing our understanding of ventilation processes in the WMED. It also serves as a benchmark for calibrating Biogeochemical-Argo floats and for validating regional biogeochemical models. The dataset is publicly available at https://doi.org/10.1594/PANGAEA.982858 (Belgacem et al., 2025).