High‐Resolution Assessment of SST Summer Cycle Changes in the Mediterranean Sea (1982–2024): A Multi‐Scale Phenological Analysis

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Abstract Accelerated ocean warming from greenhouse gas emissions is altering marine thermal cycles globally. While ocean warming is well documented, its impacts on Sea Surface Temperature (SST) seasonal cycles remain less understood, particularly in the Mediterranean Sea. Summer SST exhibits the highest warming trends, yet summer cycle dynamics are poorly characterized. Understanding these changes is critical to anticipate impacts on climate processes and marine ecosystems. In this study, 43 years (1982–2024) of daily SST data across the Mediterranean Basin were analyzed, with a focus on the summer period. Key phenological metrics were extracted: onset, end, duration, phase (defined as the timing of maximum SST in the seasonal cycle maximum), SST at onset/end, maximum SST, and amplitude. Results revealed statistically significant shifts. Start of season advanced significantly ( p < 0.05) at −2.01 ± 1.76 days decade −1 , end delayed +3.27 ± 2.65 days decade −1 ( p < 0.05), extending Summer by 4.24 ± 3.29 days decade −1 ( p < 0.05), which corresponds to ∼17.80 ± 13.81 days. Time of maximal SST shows no significant basin‐scale trends, although significant regional advances occurred within a very limited part of the study area. Annual cycle amplitude increased by +0.40 ± 0.36°C in 40 years ( p < 0.01) over the entire Mediterranean Sea. Strong correlations emerged between warming SST and phenological shifts, directly linking temperature increase to the changes occurring in the summer SST cycle. By explicitly quantifying SST seasonal cycles, this study provides critical baselines for assessing ecosystem responses to accelerated seasonal changes within the warming Mediterranean.

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