The consistent in-situ global gridded temperature and salinity dataset, CORA OA 1960-2024

Observations of seawater temperature and salinity as the main source of information on large-scale ocean currents

Abstract A. S. Sarkisyan developed a diagnostic method in the 1960s, based on the inclusion of annual mean temperature and salinity fields in circulation models, which made it possible to simulate climatic currents in the World Ocean and a number of other marine basins. As observations of seawater temperature and salinity accumulated, their climatic seasonal cycle became available on regular grids for several marine areas. Therefore, A. S. Sarkisyan and his followers extended the diagnostic method by proposing a set of algorithms, including nudging, which allowed the simulation of seasonal circulation for any individual marine basin. Recently, the possibility has emerged of using daily eddy-resolving three-dimensional temperature and salinity fields reconstructed from satellite observations on a regular grid. This makes it possible to apply nudging to the reanalysis of the Black Sea state and to off-line field analysis of the World Ocean. Nudging has shown good correspondence with similar results obtained by more complex assimilation schemes. Based on these results and developing the ideas of A. S. Sarkisyan that the key information about ocean currents is contained in the spatial distribution of the density field, an economical algorithm for four-dimensional variational assimilation of temperature and salinity observations in an ocean circulation model is proposed here.

Multi-decadal high-resolution historical simulations with the ECMWF global atmosphere model

This paper describes an ensemble of global atmosphere reference simulations covering the period 1980 to 2023 produced with the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS). The resulting dataset consists of 6-hourly three-dimensional global outputs from higher- and lower-resolution configurations of the IFS, which have average horizontal grid spacings of ~9 km (one ensemble member) and ~28 km (ten ensemble members), respectively. The atmosphere is constrained by high-resolution satellite-based estimates of daily mean sea surface temperature and sea ice concentration and time-evolving external climate forcings, including observed greenhouse gas and estimated aerosol concentrations. These data were produced as part of the European Eddy-Rich Earth System Models (EERIE) project and will serve as a reference for corresponding ocean-atmosphere coupled simulations and idealised sensitivity experiments. We have made this dataset publicly available and expect it to be a valuable resource for scientific research and other applications that extend beyond the lifetime of the EERIE project.

Historical Nansen Cast Temperature Profiles and the Ocean Heat Content 1 Change since 19 th Century 2

Interannual Variability of Surface Salinity of the Northwestern Shelf of the Black Sea Based on Satellite Information and Reanalysis Data

Influence of local and remote climate processes on driving the salinification followed by freshening phases in the eastern Arabian Sea

Sea surface salinity (SSS) modulates upper-ocean stratification, air–sea coupling, and freshwater redistribution in the North Indian Ocean, yet its interannual variability in the eastern Arabian Sea (EAS) remains insufficiently quantified. This study evaluates satellite-derived SSS from the Soil Moisture and Ocean Salinity, Soil Moisture Active Passive, and European Space Agency-Climate Change Initiative (CCI) products using high-precision shipborne measurements across the EAS. Validation results show that CCI SSS exhibits strong agreement with in situ observations and best reproduces the spatiotemporal variability of the in situ gridded dataset (Willmott skill score 0.81). CCI also exhibit relatively lower spatial root-mean-square error (0.93 PSU) compared to other Satellite derived datasets. The analysis of interannual SSS variability using the CCI dataset during 2010–2023 reveals two contrasting regimes: a salinification phase during 2015–2019 (+0.5 PSU) followed by a pronounced freshening phase during 2020–2023 (−0.5 PSU). Analysis of precipitation, ocean circulation, and climate indices indicates that reduced rainfall and weak horizontal advection dominated the salinification phase. In contrast, the freshening phase was driven by enhanced precipitation and intensified freshwater transport from the Bay of Bengal. This period coincides with the rare triple-dip La Niña (2020–2022), which strengthened coastal Kelvin waves and the East India Coastal Current, facilitating transport of low-salinity waters through the “River-in-the-Sea”(RIS) pathway. These results highlight the sensitivity of EAS salinity to coupled local and remote freshwater processes and demonstrate the importance of multi-sensor satellite SSS products for monitoring climate-driven hydrological variability.

Assessing Mediterranean Sea temperature and salinity trends using Argo float data and reanalysis products between 2012 and 2025

This study compares temperature and salinity changes in the Mediterranean Sea over the period 2012–2025, using Argo float profiles and operational reanalysis products in three open-sea regions: the Western Mediterranean, Ionian, and Levantine basins. The temporal evolution of conservative temperature and absolute salinity is examined using Hovmöller diagrams (time–depth), and linear regression is applied to quantify long-term trends. The results reveal consistent and significant warming in the Western Mediterranean and Ionian Sea, with trends reaching 0.8-0.9 °C per decade near the surface. In contrast, a negative salinity trend (up to -0.2 g kg - ¹ per decade) in the upper 100 m is observed, likely linked to the freshening of the North Atlantic. The intermediate layers associated with Levantine Intermediate Water exhibit a clear increase in salinity, up to 0.1 g kg - ¹ per decade, indicating ongoing modification of this key Mediterranean water mass. While significant discrepancies arise in the upper water column of the Ionian and Levantine seas due to sparser and intermittent Argo coverage and higher variability, both datasets consistently indicate warming and salinification below 800 m. Near the surface, reanalysis temperature trends significantly exceed those found with Argo data in both the Ionian and Levantine seas. In contrast, Argo salinity trends are larger compared to reanalysis in the upper Levantine Sea, but they are comparable in the surface Ionian. Overall, these findings confirm that the Mediterranean Sea continues to experience significant warming and subsurface salinification, and that these trends can be effectively monitored by Argo floats, provided sufficient spatial coverage across all subbasins. The persistence of these trends through 2025 highlights the continuing impact of global climate change on the Mediterranean thermohaline structure.