he 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1000 previously unpublished high-resolution vertical profiles of CTD-O2 measurements mostly collected within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).
DOI: 10.5194/essd-17-5315-2025
Publication Date: 2025-10-14