Global ocean warming continued unabated in 2025 in response to increased greenhouse gas concentrations and recent reductions in sulfate aerosols, reflecting the long-term accumulation of heat within the climate system, with conditions evolving toward La Niña during the year. In 2025, global upper 2000 m ocean heat content (OHC) increased by ∼23 ± 8 ZJ relative to 2024 according to IAP/CAS estimates. CIGAR-RT, and Copernicus Marine data confirm the continued ocean heat gain. Regionally, about 33

The mean kinematic features in the Gulf of Gab & egrave;s region are analyzed based on 30 years of altimetry data (1993-2022) and the outputs of a high-resolution ocean model for the year 2022. A comparison of the seasonal variability in three different geographical areas within the gulf is presented. In the northern and southern parts of the gulf, anticyclonic structures prevail, while the central area is dominated by divergence. Similarity in flow topology is found in these three areas of the gulf due to the signature of hyperbolic regions. In winter and fall, the mean flow is oriented northward, while it is reversed in spring and summer. The tidal perturbations influence sea level, kinetic energy and hyperbolic geostrophic structures, leading to the generation of a cyclonic current in the central part of the gulf and to the presence of persistent strain gradients amplifying hyperbolic structures. The finite-time Lyapunov exponent (FTLE) computed using altimetry data highlights the link between physical and biogeochemical dispersion, with the Gulf of Gab & egrave;s mean circulation features acting as transport barriers for phytoplankton dispersion.

Heating in the ocean has continued in 2024 in response to increased greenhouse gas concentrations in the atmosphere, despite the transition from an El Niño to neutral conditions. In 2024, both global sea surface temperature (SST) and upper 2000 m ocean heat content (OHC) reached unprecedented highs in the historical record. The 0–2000 m OHC in 2024 exceeded that of 2023 by 16 ± 8 ZJ (1 Zetta Joules = 1021 Joules, with a 95

As climate change impacts ocean properties, such as temperatures, salinity and stratification, the Atlantic Meridional Overturning Circulation (AMOC) may be at risk of collapse. A weakened AMOC can be connected to shifts in global weather patterns, such as more heatwaves in Europe. The outflow water from the Mediterranean Sea has properties that influence the North Atlantic Ocean hydrodynamics and the AMOC. The Mediterranean Outflow Water (MOW) properties vary due to climate change, affecting the Atlantic Ocean thermohaline characteristics. Using a multi-data approach, this study compares four reanalyses of different horizontal grid resolutions in a seventy years time span (RR 1955-2015 DOI: 10.25423/MEDSEA_REANALYSIS_PHY_006_009, MEDREA16 1987-2018 DOI:10.25423/medsea_reanalysis_phys_006_004, MEDREA24 1987-2024 DOI: 10.25423/CMCC/MEDSEA_MULTIYEAR_PHY_006_004_E3R1, CIGAR-CS 1961-2022 http://cigar.ismar.cnr.it/) to the World Ocean Atlas 2023 climatology (DOI: 10.25921/va26-hv25) and mooring observations at the Espartel Sill. The study evaluates volume, heat and salt transports, temperature and salinity time series at Gibraltar and analyzes the MOW decadal variability in the North Atlantic from 1955 to 2024.The goal of this research is to assess the consistency and accuracy of multiple reanalysis products in simulating the Mediterranean Sea and Atlantic Ocean interaction and to establish how the model resolution and geometry affect the MOW characteristics. Ultimately, this assists in understanding how MOW variability may impact the AMOC.

Joint Meeting of IQuOD, GTSPP, SOOP, and XBT Science Groups What:More than 50 international experts of ocean observations, data quality control, and data management came together, under the umbrella of the International Oceanographic Data and Information Exchange (IODE) of the Intergovernmental Oceanographic Commission (IOC) of UNESCO, to explore future collaborations and synergies for the efficient ocean in situ data and products provision (https://oceanexpert.org/event/4431). When:11-15 November 2024 Where: Bologna (Italy) and online

The advent of open science and the United Nations Decade of Ocean Science for Sustainable Development are revolutionizing the ocean-data-sharing landscape for an efficient and transparent ocean information and knowledge generation. This blue revolution raised awareness on the importance of metadata and community standards to activate interoperability of the digital assets (data and services) and guarantee that data-driven science preserves provenance, lineage and quality information for its replicability. Historical data are frequently not compliant with these criteria, lacking metadata information that was not retained, crucial at the time of data generation and further ingestion into marine data infrastructures. The present data review is an example attempt to fill this gap through a thorough data reprocessing starting from the original raw data and operational log sheets. The data gathered using XBT (eXpendable BathyThermograph) probes during several monitoring activities in the Tyrrhenian and Ligurian seas between 1999 and 2019 have first been formatted and standardized according to the latest community best practices and all available metadata have been inserted, including calibration information never applied, uncertainty specification and bias correction from Cheng et al. (2014). Secondly, a new automatic quality control (QC) procedure has been developed and a new interpolation scheme applied. The reprocessed (REP) dataset has been compared to the data version, presently available from the SeaDataNet (SDN) data access portal, processed according to the pioneering work of Manzella et al. (2003) conducted in the framework of the European Union Mediterranean Forecasting System Pilot Project (Pinardi et al., 2003). The comparison between REP and SDN datasets has the objective to highlight the main differences derived from the new data processing process. The maximum discrepancy among the REP and SDN data versions always resides within the surface layer (REP profiles are warmer than SDN ones) until 150 m depth generally when the thermocline settles (from June to November). The overall bias and root mean square difference are equal to 0.002 and 0.041 degrees C, respectively. Such differences are mainly due to the new interpolation technique (Barker and McDougall, 2020) and the application of the calibration correction in the REP dataset. The REP dataset (Reseghetti et al., 2024; 10.13127/rep_xbt_1999_2019.2) is available and accessible through the INGV (Istituto Nazionale di Geofisica e Vulcanologia, Bologna) ERDDAP (Environmental Research Division's Data Access Program) server, which allows for machine-to-machine data access in compliance with the FAIR (findable, accessible, interoperable and reusable) principles (Wilkinson et al., 2016).

A high-quality hydrographic observational database is essential for ocean and climate studies and operational applications. Because there are numerous global and regional ocean databases, duplicate data continues to be an issue in data management, data processing and database merging, posing a challenge on effectively and accurately using oceanographic data to derive robust statistics and reliable data products. This study aims to provide algorithms to identify the duplicates and assign labels to them. We propose first a set of criteria to define the duplicate data; and second, an open-source and semi-automatic system to detect duplicate data and erroneous metadata. This system includes several algorithms for automatic checks using statistical methods (such as Principal Component Analysis and entropy weighting) and an additional expert (manual) check. The robustness of the system is then evaluated with a subset of the World Ocean Database (WOD18) with over 600,000 in-situ temperature and salinity profiles. This system is an open-source Python package (named DC_OCEAN) allowing users to effectively use the software. Users can customize their settings. The application result from the WOD18 subset also forms a benchmark dataset, which is available to support future studies on duplicate checks, metadata error identification, and machine learning applications. This duplicate checking system will be incorporated into the International Quality-controlled Ocean Database (IQuOD) data quality control system to guarantee the uniqueness of ocean observation data in this product.

The Mediterranean Sea is experiencing accelerated warming, outpacing the global ocean average according to recent studies. This regional basin is particularly susceptible to the effects of climate change due to its unique topography and thermohaline circulation patterns. Observational data and model reanalysis have documented significant changes in the characteristics of Mediterranean water masses.One of the best indicators of this alarming trend is the Ocean Heat Content (OHC). The challenge of this research manifests in the implementation of a cloud-based workflow to estimate the OHC, assessing its evolution in user-defined sub-regions or depth layers within the Mediterranean basin. This application developed within the EU Blue Cloud 26 project framework, has the ambition to access data machine-to-machine data from multiple blue data infrastructures (SeaDataNet, Copernicus Marine Service, EuroArgo, World Ocean Database) available to the scientific community.The workflow will use the DIVAnd tool to map historical in situ temperature data on a regular grid and the results will be compared to ocean reanalysis products from INGV and the Copernicus Marine Service.The analysis will focus on identifying OHC trends, with a specific emphasis on understanding the implications of these changes for the region's climate system.We expect the results to highlight the spatial variability of warming trends within different sub-regions and depth layers, underscoring the complex interplay between hydrodynamics and climate change in shaping the Mediterranean's thermal structure.Moreover, by leveraging this workflow, we ensure that ocean key variables are consistently updated and validated according to the most recent community practices. The effort conducted will allow us to have a key indicator, such as OHC, rapidly available and constantly updated according to the most recent data, thus supporting an informed and efficient decision.Finally, this study will contribute to the broader understanding of regional climate dynamics and provide valuable insights into the diagnosis and projection of extreme weather events in the Mediterranean Sea within the context of a changing climate environment.

The global physical and biogeochemical environment has been substantially altered in response to increased atmospheric greenhouse gases from human activities. In 2023, the sea surface temperature (SST) and upper 2000 m ocean heat content (OHC) reached record highs. The 0–2000 m OHC in 2023 exceeded that of 2022 by 15 ± 10 ZJ (1 Zetta Joules = 10 21 Joules) (updated IAP/CAS data); 9 ± 5 ZJ (NCEI/NOAA data). The Tropical Atlantic Ocean, the Mediterranean Sea, and southern oceans recorded their highest OHC observed since the 1950s. Associated with the onset of a strong El Niño, the global SST reached its record high in 2023 with an annual mean of ∼0.23°C higher than 2022 and an astounding > 0.3°C above 2022 values for the second half of 2023. The density stratification and spatial temperature inhomogeneity indexes reached their highest values in 2023.

AbstractDespite the progress in the international and regional governance efforts at the level of climate change, ocean acidification (OA) remains a global problem with profoundly negative environmental, social, and economical consequences. This requires extensive mitigation and adaptation effective strategies that are hindered by current shortcomings of governance. This multidisciplinary chapter investigates the risks of ocean acidification (OA) for aquaculture and fisheries in the Mediterranean Sea and its sub-basins and the role of regional adaptive governance to tackle the problem. The identified risks are based on the biological sensitivities of the most important aquaculture species and biogenic habitats and their exposure to the current and future predicted (2100) RCP 8.5 conditions. To link OA exposure and biological sensitivity, we produced spatially resolved and depth-related pH and aragonite saturation state exposure maps and overlaid these with the existing aquaculture industry in the coastal waters of the Mediterranean basin to demonstrate potential risk for the aquaculture in the future. We also identified fisheries’ vulnerability through the indirect effects of OA on highly sensitive biogenic habitats that serve as nursery and spawning areas, showing that some of the biogenic habitats are already affected locally under existing OA conditions and will be more severely impacted across the entire Mediterranean basin under 2100 scenarios. This provided a regional vulnerability assessment of OA hotspots, risks and gaps that created the baseline for discussing the importance of adaptive governance and recommendations for future OA mitigation/adaptation strategies. By understanding the risks under future OA scenarios and reinforcing the adaptability of the governance system at the science-policy interface, best informed, “situated” management response capability can be optimised to sustain ecosystem services.

The in-situ data gathered over two decades since mid-1990s in the South-Eastern Levantine Basin from 34 hydrographic campaigns and from 35 bi-weekly and monthly Voluntary Observing Ships (VOS) transects, after the pioneering POEM cruises, have provided insight on the dominant meso-scale coherent circulation features of this sub-basin. The most pronounced feature, the anticyclonic Cyprus Eddy, migrates over the broad region of the Eratosthenes seamount and exhibits significant seasonal and inter-annual spatial-temporal variability. Another prominent structure of the sub-basin is the anticyclonic Shikmona Eddy generated by instabilities of the strong northward flowing jet along the south-easternmost shelf and slope of the Levantine basin. Its evolution and co-existence with the Cyprus Eddy, cause the periodic re-establishment of the Shikmona Gyre, which was first observed during the POEM cruises in mid-1980s. The offshore, cross basin, eastward flowing Mid-Mediterranean Jet (MMJ) defines the northern and southern flanks of these sub-basin scale anticyclonic eddies and transports the lower salinity Modified Atlantic Water (MAW) in the subsurface layer, through the warmest and most saline waters of the Mediterranean. Periodically, the MMJ bifurcates and/or is diverted northward, along the western coast of Cyprus due to westward and northward spatial fluctuations of the Cyprus Eddy’s western boundaries. The current long term in-situ monitoring of the sub-basin provides an overview of the extent of the main water masses and characterizes their variability throughout the period considered. The analysis of the data indicates an increase of the temperature and salinity of the Levantine Surface Water (LSW) and of the subsurface MAW. The Eastern Mediterranean Transient Water (EMTW) is shown to occupy the deep cavities in the vicinity of the Eratosthenes seamount while its upper boundary was found to be lifted to shallower depths over a period of two decades.

Changes in ocean heat content (OHC), salinity, and stratification provide critical indicators for changes in Earth’s energy and water cycles. These cycles have been profoundly altered due to the emission of greenhouse gasses and other anthropogenic substances by human activities, driving pervasive changes in Earth’s climate system. In 2022, the world’s oceans, as given by OHC, were again the hottest in the historical record and exceeded the previous 2021 record maximum. According to IAP/CAS data, the 0–2000 m OHC in 2022 exceeded that of 2021 by 10.9 ± 8.3 ZJ (1 Zetta Joules = 10 21 Joules); and according to NCEI/NOAA data, by 9.1 ± 8.7 ZJ. Among seven regions, four basins (the North Pacific, North Atlantic, the Mediterranean Sea, and southern oceans) recorded their highest OHC since the 1950s. The salinity-contrast index, a quantification of the “salty gets saltier—fresh gets fresher” pattern, also reached its highest level on record in 2022, implying continued amplification of the global hydrological cycle. Regional OHC and salinity changes in 2022 were dominated by a strong La Niña event. Global upper-ocean stratification continued its increasing trend and was among the top seven in 2022.

An analysis of in-situ data gathered over the two decade post POEM period in the South-Eastern Levantine Basin from extensive hydrographic (CTD) campaigns and VOS XBT transects, along with data provided by the latest SeaDataCloud Mediterranean Sea Temperature and Salinity climatology (http://dx.doi.org/10.12770/3f8eaace-9f9b-4b1b-a7a4-9c55270e205a) and the Mediterranean Sea Physics Reanalysis from the Copernicus Marine Service (CMS; https://data.marine.copernicus.eu/product/MEDSEA_MULTIYEAR_PHY_006_004), have all provided insight on the dominant, coherent, meso-scale, circulation features as well as the evolution and variability of the thermohaline properties of the main water masses in this sub-basin. The most pronounced feature, the warm core Cyprus Eddy, migrates over the broad region of the Eratosthenes seamount and exhibits significant seasonal and inter-annual spatio-temporal variability. Another prominent structure is the anticyclonic Shikmona Eddy generated periodically due to instabilities of the strong northward flowing jet along the south-easternmost shelf and slope of the Levantine basin. Its evolution and co-existence with the Cyprus Eddy for periods of a few months, affects the temporal re-establishment of the Shikmona Gyre, which was first observed during the POEM cruises in the mid 1980s. The eastward flowing Mid Mediterranean Jet (MMJ) defines the northern flanks of these sub-basin scale eddies and transports the lower salinity Modified Atlantic Water (MAW) through the warmest and most saline region of the Mediterranean. Periodically the MMJ bifurcates and/or is diverted northward, along the western coast of Cyprus due to spatial fluctuations of the Cyprus Eddy. Four active periods were identified with either a dominant Cyprus Eddy only or coexisting Cyprus and Shikmona Eddies. This long term in-situ monitoring also provides an overview of the extent of the main water masses and characterizes their variability throughout the period considered. The temperature and salinity of the Levantine Surface Water (LSW) and of the subsurface MAW have increased. The Eastern Mediterranean Transient Water (EMTW) is shown to occupy the deep cavities, below the Eastern Mediterranean Deep Water (EMDW), in the vicinity of the Eratosthenes seamount while its upper boundary was lifted to shallower depths over the same period.

The relationship between the isotopic composition of precipitation in the Mediterranean Sea, the atmospheric circulation patterns over the region and groundwater properties has been topic of investigation in recent years. Overall, the link between the isotopic composition of precipitation and the Mediterranean climate raises the question of how future climate change could affect the isotope ratios of precipitation and groundwater. Past and future atmospheric properties (i.e. humidity, evaporation, precipitation and winds) over the Mediterranean region can be used to investigate the past and possibly understand future characteristics of meteoric water isotope composition. In order to evaluate how the climate change will affect the isotope composition of meteoric water, we re-evaluated previous rain events in light of well-defined climate framework. The main objective is to retrieve information on the atmospheric circulation systems based on ERA5 reanalysis and relate climate features with the isotope composition of selected rain events. This will allow to identify the most appropriate parameters needed to constrain the circulation systems responsible for those events and their isotope composition. Preliminary results to infer scenario-based considerations on the evolution of the meteoric recharge will be shown and discussed.

SOURCE utility for reprocessing, calibration, and evaluation is a software designed for web applications that permits to calibrate and validate ocean models within a selected spatial domain using in-situ observations. Nowadays, in-situ observations can be freely accessed online through several marine data portals together with the metadata information about the data provenance and its quality. Metadata information and compliance with modern data standards allow the user to select and filter the data according to the level of quality required for the intended use and application. However, the available data sets might still contain anomalous data, bad data flagged as good, due to several reasons, i.e., the general quality assurance procedures adopted by the data infrastructure, the selected data type, the timeliness of delivery, etc. In order to provide accurate model skill scores, the SOURCE utility performs a secondary quality check, or re-processing, of observations through gross check tests and a recursive statistical quality control. This first and basic SOURCE implementation uses Near Real Time moored temperature and salinity observations distributed by the Copernicus Marine Environment and Monitoring Service (CMEMS) and two model products from Istituto Nazionale di Geofisica e Vulcanologia (INGV), the first an analysis and the second a reanalysis, distributed during CMEMS phase I for the Mediterranean Sea. The SOURCE tool is freely available to the scientific community through the ZENODO open access repository, consistent with the open science principles and for that it has been designed to be relocatable, to manage multiple model outputs, and different data types. Moreover, its observation reprocessing module provides the possibility to characterize temperature and salinity variability at each mooring site and continuously monitor the ocean state. Highest quality mooring time series at 90 sites and the corresponding model values have been obtained and used to compute model skill scores. The SOURCE output also includes mooring climatologies, trends, Probability Density Functions and averages at different time scales. Model skill scores and site statistics can be used to visually inspect both model and sensor performance in Near Real Time at the single site or at the basin scale. The SOURCE utility uptake allows the interested user to adapt it to its specific purpose or domain, including for example additional parameters and statistics for early warning applications.

Pialassa Baiona is a shallow temperate coastal lagoon influenced by a variety of factors, including regional climate change and local anthropogenic disturbances. To better understand how these factors influenced modern organic carbon (OC) sources and accumulation rates, we measured OC as well as stable carbon isotopes (delta C-13) in Pb-210-dated sediments within a vegetated saltmarsh habitat and a human impacted habitat. Relative Sea Level (RSL) at the nearby tide gauge station data and four different Sea Surface Temperature (SST) data sets were analyzed starting from 1900 to assess the potential effect of sea ingression and warming on the coastal lagoon sedimentary processes. The source contribution calculated from the MixSIAR Bayesian model revealed a mixed composition of sedimentary OC, dominated by an increase in marine-derived OC after the 1950s, matching with a decrease from autochthonous saltmarsh vegetation (Juncus spp.) in the saltmarsh habitat, and from riverine/estuarine-derived OC in the impacted habitat. RSL rise in the area (8.7 +/- 0.5 mm yr-1 in the period 1900-2014) has been mainly driven by the land subsidence, especially during the central decades of the last century, enhancing the sea ingression into the lagoon. RSL rise influenced changes in sedimentary OC sources and accumulation at different level within the two habitats from the 1950s onward; conversely, no direct effect of SST was detected. (c) 2022 Elsevier B.V. All rights reserved.

The increased concentration of greenhouse gases in the atmosphere from human activities traps heat within the climate system and increases ocean heat content (OHC). Here, we provide the first analysis of recent OHC changes through 2021 from two international groups. The world ocean, in 2021, was the hottest ever recorded by humans, and the 2021 annual OHC value is even higher than last year’s record value by 14 ± 11 ZJ (1 zetta J = 1021 J) using the IAP/CAS dataset and by 16 ± 10 ZJ using NCEI/NOAA dataset. The long-term ocean warming is larger in the Atlantic and Southern Oceans than in other regions and is mainly attributed, via climate model simulations, to an increase in anthropogenic greenhouse gas concentrations. The year-to-year variation of OHC is primarily tied to the El Niño-Southern Oscillation (ENSO). In the seven maritime domains of the Indian, Tropical Atlantic, North Atlantic, Northwest Pacific, North Pacific, Southern oceans, and the Mediterranean Sea, robust warming is observed but with distinct inter-annual to decadal variability. Four out of seven domains showed record-high heat content in 2021. The anomalous global and regional ocean warming established in this study should be incorporated into climate risk assessments, adaptation, and mitigation.

The needs of society and the emerging blue economy require access and integration of data and information for the construction of dedicated products. A "transparent and accessible ocean" is one of the key objectives of the Ocean Decade 2021–30. In this context, marine infrastructures become significant components of a global knowledge environment, enabling environmental assessment and providing the necessary data for scientifically valid actions to protect and restore ocean health, to use marine resources in a sustainable way. The data is collected, analyzed, organized, and used by people and their good use/reuse can be obtained with social practices, technological and physical agreements aimed at facilitating collaborative knowledge, decision-making, inference. The vision is a digital ocean data ecosystem made up of multiple, interoperable, and scalable components. The huge amount of data and the resulting products can drive the development of new knowledge as well as new applications and services. Predictive capabilities that derive from the digital ecosystem enable the implementation of services for real-time decision-making, multihazard warning systems, and advance marine space planning. The chapter develops following the progressive complexity and information content of products deriving from oceanic data: data cycle and data collections, data products, oceanic reanalysis. The chapter discusses the new challenges of data products and the complexity of deriving them.

We present a skillful deep learning algorithm for supporting quality control of ocean temperature measurements, which we name SalaciaML according to Salacia the roman goddess of sea waters. Classical attempts to algorithmically support and partly automate the quality control of ocean data profiles are especially helpful for the gross errors in the data. Range filters, spike detection, and data distribution checks remove reliably the outliers and errors in the data, still wrong classifications occur. Various automated quality control procedures have been successfully implemented within the main international and EU marine data infrastructures (WOD, CMEMS, IQuOD, SDN) but their resulting data products are still containing data anomalies, bad data flagged as good and vice-versa. They also include visual inspection of suspicious measurements, which is a time consuming activity, especially if the number of suspicious data detected is large. A deep learning approach could highly improve our capabilities to quality assess big data collections and contemporary reducing the human effort. Our algorithm SalaciaML is meant to complement classical automated quality control procedures in supporting the time consuming visually inspection of data anomalies by quality control experts. As a first approach we applied the algorithm to a large dataset from the Mediterranean Sea. SalaciaML has been able to detect correctly more than 90% of all good and/or bad data in 11 out of 16 Mediterranean regions.