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

Abstract

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.