Seasonal variability of sea temperature profiles in the central Mediterranean

Abstract

This study investigates the seasonal variability of sea temperature profiles across eight purposefully chosen sites in the Central Mediterranean, with a focus on how stratification and internal structures such as the thermocline, respond to surface warming and regional oceanographic processes. Using two years of high-resolution numerical temperature data, the analysis explores temporal and spatial differences in temperature profiles, gradient profiles, thermocline depth, thickness, intensity, and boundary limits. A range of statistical techniques, including Pearson correlations, cross-correlation analysis, autocorrelation and partial autocorrelation functions, were used to explore the links between both sea surface temperature and thermocline features, as well as between thermocline depth and other thermocline metrics. Results revealed consistent seasonal cycles, with weak stratification and deep mixing during winter, and a sharp, shallow thermocline forming in summer. While this seasonal signal was evident across all sites, numerous regional differences emerged where some sites exhibited deeper and more stable thermoclines whilst other locations demonstrated more variable behaviour, often influenced by mesoscale features such as eddies or coastal currents. Sea surface temperature was linked to a thicker, stronger, and shallower thermocline, with temperature changes at the surface typically preceding changes in subsurface structure. Thermocline depth also showed strong internal associations, reflecting how its position influences both the range and sharpness of the stratified layer. The autocorrelation and partial autocorrelation results showed that thermocline features typically follow a strong yearly pattern, where values tend to repeat from one year to the next, and summer conditions are usually the opposite of those in winter. These findings support the study’s hypothesis that seasonal heating, modified by regional mesoscale circulation and dynamics, drives the evolution of temperature stratification. The results contribute to a more refined understanding of thermal structure in semi-enclosed seas and provide a basis for future forecasting or modelling efforts concerning stratification dynamics.