The Western MEDiterranean Sea BioGeochemical Climatology (BGC-WMED, https://doi.org/10.1594/PANGAEA.930447) (Belgacem et al., 2021) presented here is a product derived from quality-controlled in situ observations. Annual mean gridded nutrient fields for the period 1981–2017 and its sub-periods 1981–2004 and 2005–2017 on a horizontal $\mathrm{1}/\mathrm{4}$ ^∘ × $\mathrm{1}/\mathrm{4}$ ^∘ grid have been produced. The biogeochemical climatology is built on 19 depth levels and for the dissolved inorganic nutrients nitrate, phosphate and orthosilicate. To generate smooth and homogeneous interpolated fields, the method of the variational inverse model (VIM) was applied. A sensitivity analysis was carried out to assess the comparability of the data product with the observational data. The BGC-WMED was then compared to other available data products, i.e., the MedBFM biogeochemical reanalysis of the Mediterranean Sea and the World Ocean Atlas 2018 (WOA18) (its biogeochemical part). The new product reproduces common features with more detailed patterns and agrees with previous records. This suggests a good reference for the region and for the scientific community for the understanding of inorganic nutrient variability in the western Mediterranean Sea, in space and in time, but our new climatology can also be used to validate numerical simulations, making it a reference data product.

Long-term time series are a fundamental prerequisite to understanding and detecting climate shifts and trends. Understanding the complex interplay of changing ocean variables and the biological implication for marine ecosystems requires extensive data collection for monitoring, hypothesis testing, and validation of modelling products. In marginal seas, such as the Mediterranean Sea, there are still monitoring gaps, both in time and in space. To contribute to filling these gaps, an extensive dataset of dissolved inorganic nutrient observations (nitrate, phosphate, and silicate) was collected between 2004 and 2017 in the western Mediterranean Sea and subjected to rigorous quality control techniques to provide to the scientific community a publicly available, long-term, quality-controlled, internally consistent biogeochemical data product. The data product includes 870 stations of dissolved inorganic nutrients, including temperature and salinity, sampled during 24 cruises. Details of the quality control (primary and secondary quality control) applied are reported. The data are available in PANGAEA (https://doi.org/10.1594/PANGAEA.904172, Belgacem et al., 2019).

Earth’s oceans contain large numbers of cyclonic eddies, 10 to 25 kilometers in diameter and unresolved in climate simulations. However, we lack observations of these features due to their small size and fast evolution. Here, we present in situ observations of one such cyclonic eddy with intense chlorophyll at its center as it spontaneously splits into two smaller cyclonic eddies over a few days. This splitting rapidly transports surface waters to depth, with sustained vertical velocities of 60 meters per day, primarily from the center of the eddy where carbon concentrations are largest, facilitating efficient transfer of phytoplankton carbon to depth, below the well-mixed, sunlit surface layer. We reproduce the splitting process in an idealized ocean model and find that splitting is controlled by the initial elliptical eddy shape, size, and intensity. Our observations uncover a mechanism for subduction in the upper ocean and highlight the need for quantifying its global prevalence.

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).

Long-term time-series are a fundamental prerequisite to understand and detect climate shifts and trends. Understanding the complex interplay of changing ocean variables and the biological implication for marine ecosystems requires extensive data collection for monitoring and hypothesis testing and validation of modelling products. In marginal seas, such as Mediterranean Sea, there are still monitoring gaps, both in time and in space. To contribute filling these gaps, an extensive dataset of dissolved inorganic nutrients profiles (nitrate, NO₃; phosphate, PO₄³⁻; and silicate, SiO₂) have been collected between 2004 and 2017 in the Western Mediterranean Sea and subjected to quality control techniques to provide to the scientific community a publicly available, long-term, quality controlled, internally consistent biogeochemical data product. The database includes 870 stations of dissolved inorganic nutrients sampled during 24 cruises, including temperature and salinity. Details of the quality control (primary and secondary quality control) applied are reported. The data are available in PANGAEA (https://doi.org/10.1594/PANGAEA.904172, Belgacem et al. 2019).

A new dataset from oceanographic cruises in the Western Mediterranean Sea (WMED) was compiled to integrate the previously published regional data product about dissolved inorganic nutrients CNR-DIN-WMED about dissolved inorganic nutrients (https://doi.org/10.1594/PANGAEA.904172, Belgacem et al., 2019, 2020). The Mediterranean region is experiencing rapid changes, necessitating high-quality and reliable datasets. However, the scarcity of the in-situ observations hinders the understanding of these changes and their impact on biogeochemical cycles. Dissolved oxygen is a vital component of marine ecosystems and plays a fundamental role in governing nutrient and carbon cycles, underscoring the need for accurate and reliable data. To address this, a high resolution, regional-scale data product was developed to understand decadal variability and spatial/temporal patterns of the ventilation process in the WMED. This study presents an extensive collection of unpublished dissolved oxygen data from continuous sensors collected between 2004 and 2023, along with a description of the quality assurance procedures. The quality assurance process involves calibration of CTD measurements against Winkler analyses and the comparison of deep observations with reference datasets, using the crossover analysis. The resulting data product O2WMED can be used as reference for assessing oxygen sensors mounted on biogeochemical Argo (BGC-Argo) floats or Gliders and for regional model validation.