Understanding the climate of the past, in particular seasonal temperature amplitudes, is essential to evaluate the effects of future climate change on marine ecosystems. The Mediterranean is of particular importance, because of its crucial role in modern ocean atmosphere phenomena such as the North Atlantic Oscillation (NAO). We analyzed fossil shells of the bivalve Arctica islandica collected from Pleistocene successions in Central and Southern Italy (i.e., Rome, Lecce and Sicily). According to preliminary biostratigraphic data the studied deposits belong to the middle Calabrian, between 1.2-0.9 Ma for the Sicily outcrop and 1.4-1.2 Ma for the Rome and Lecce outcrops. Prior to isotope geochemical analysis confocal Raman microscopy measurements were conducted to detect potential diagenetic alterations (e.g., from aragonite to calcite). The seasonal water temperature amplitude was reconstructed using stable oxygen isotope (δ18O) values, which were derived by micro-milling and Isotope Ratio Mass Spectrometry. Analysis of the growth patterns (on-going research) revealed ontogenetic ages of up to 210 years. These time series are used for the identification of multi-year (i.e., decadal) patterns, such as the NAO. First results of our study indicate that seasonality was remarkably low during the studied geological epoch. This is in sharp contrast to previous assumptions according to which the simultaneous occurrence of boreal (A. islandica) and warm-water species in the Mediterranean Sea during the Pleistocene can be explained by high seasonality. Different links and scenarios on a regional as well as a bigger scale will be discussed.