## 1 Introduction  
There has long been a keen theoretical and methodological interest in archaeology at elucidating the impacts of climatic and environmental change on hominin behavior, settlement, and culture in different parts of the world at different points of time [1, 2, 3, 4, 5], and how this might be mobilized to inform challenges facing our species in the 21 st century [6, 7]. In western Europe, climate changes have been variously argued to have had deep implications for Neanderthal behavior and eventual extinction [8, 9, 10], the tempo and nature of human hunter-gatherer settlement across the Last Glacial Maximum and Early-Middle Holocene [11; 12; 13], and the arrival and adaptations of the first farmers [14; 15]. Crucial to such debates, however, is the ability to develop a set of proxies that can reconstruct the impacts of broader climatic systems on local environments used by past human populations, both marine and terrestrial [16; 17; 18]. Furthermore, from a behavioral perspective, some of the most critical climatic changes impact intra-annual seasonality of temperature and rainfall, something that has been notoriously difficult to reconstruct for the past [19; 20]. The shells of marine mollusks are routinely found in many archaeological deposits due to littoral resources that were exploited by past hominins at least from the Middle Pleistocene [21; 22; 23; 24], but especially during Upper Paleolithic and Mesolithic periods [25; 26; 27]. Previous investigations have demonstrated that shell remains can offer very valuable information on human settlement and mobility patterns, as well as on subsistence strategies of these past populations [28; 29; 30; 31]. At the same time, shells can also be considered as a particularly relevant paleoenvironmental proxy in the context of exploring past marine conditions [16; 32]. Marine mollusk species have very specific environmental requirements and are very sensitive to climate change [33; 34]. Warmer conditions during the Early Holocene provoked significant changes in species representation along the Atlantic coasts of Europe compared to the Pleistocene assemblages [35; 36]. Meanwhile, the current rising of seawater temperatures is provoking a rapid expansion of the northern limit of warm-adapted marine species [37; 38]. Beyond taxonomic studies, during the last few decades, the isotopic measurement of biogenic carbonates within mollusk shells has been found to provide a highly effective paleothermometer over the course of a mollusk's lifespan [16; 20; 39; 40]. Stable oxygen isotope ratios derived from marine mollusk shells (\(\delta^{18}\mathrm{O}_{\mathrm{shell}}\)) are powerful recorders of the seasonal sea surface temperature (SST) variations experienced during the precipitation of carbonate year-round in the past [39; 41; 42; 43]. Not only that, but isotopic series can be used to define the season(s) when the mollusks were harvested by past hominin groups, thus deciphering seasonal exploitation patterns of this food supply during prehistory [44; 45; 46; 47]. Although previous studies on modern marine mollusk shells have shown a high correlation between \(\delta^{18}\mathrm{O}_{\mathrm{shell}}\) values and SST [48; 49; 50; 51], oxygen isotope fractionation is also influenced by oxygen isotope composition of the seawater (\(\delta^{18}\mathrm{O}_{\mathrm{sw}}\)) [20; 52]. This represents a significant limitation for paleeconstructions where \(\delta^{18}\mathrm{O}_{\mathrm{sw}}\) values are unknown, while the cost- and time-consuming nature of serial \(\delta^{18}\mathrm{O}_{\mathrm{shell}}\) sampling can also be prohibitive. This has led to efforts to develop independent paleothermature archives. Concentration ratios of some trace elements to calcium have been successfully tested on corals and foraminifera [53; 54; 55].