Description: Understanding past seasonal temperature variability in the ocean is essential to evaluate the effects of future climate change on marine ecosystems. Here, we estimate seasonal amplitudes and average water temperature from stable oxygen isotope (δ18Oshell) values assuming δ18Owater values of 0.9±0.1permill (V-SMOV). Fossil valves of the bivalve Arctica islandica were collected from three Pleistocene successions (middle-late Calabrian) in Italy. Biostratigraphic analyses from Tacconi Quarry deposits (Rome) indicate an age between 1.6 and 1.2 Ma, while Augusta and Cutrofiano (Lecce) successions are slightly more recent (1.1 and 0.62 Ma, respectively). Prior to carbonate geochemical analysis, we checked the shells for potential diagenetic alterations (e.g., from aragonite to calcite). Stable oxygen isotope (δ18Oshell) profiles of eleven fossil A. islandica valves all depict a relatively low seasonality scenario. δ18Oshell amplitudes vary between 0.4permill and 1.1permill implying a reconstructed seasonal water temperature amplitude of 1.7 ̊C to 4.8 ̊C. The reconstructed average water temperature for the Sicilian population (i.e., 9 valves) is 9.5±0.47 ̊C for δ18Owater 0.9±0.1permill and coincides well with temperature requirements for modern A. islandica. The low seasonality scenario (ca. 3 ̊C) represented by the shells and the low reconstructed water temperatures, colder than modern water temperatures let to the conclusion that the shells lived during a maximum glacial phase when relatively constant water temperatures prevailed throughout the year.

Description: 87Sr/86Sr reference maps (isoscapes) are a key tool for investigating past human and animal migrations. However, there is little understanding of which biosphere samples are best proxies for local bioavailable Sr when dealing with movements of past populations. In this study, biological and geological samples (ground vegetation, tree leaves, rock leachates, water, soil extracts, as well as modern and archeological animal teeth and snail shells) were collected in the vicinity of two early medieval cemeteries (“Thuringians”, 5–6th century AD) in central Germany, in order to characterize 87Sr/86Sr of the local biosphere. Animal tooth enamel is not appropriate in this specific context to provide a reliable 87Sr/86Sr baseline for investigating past human migration. Archeological faunal teeth data (pig, sheep/goat, and cattle) indicates a different feeding area compared to that of the human population and modern deer teeth 87Sr/86Sr suggest the influence of chemical fertilizers. Soil leachates do not yield consistent 87Sr/86Sr, and 87Sr/86Sr of snail shells are biased towards values for soil carbonates. In contrast, water and vegetation samples seem to provide the most accurate estimates of bioavailable 87Sr/86Sr to generate Sr isoscapes in the study area. Long-term environmental archives of bioavailable 87Sr/86Sr such as freshwater bivalve shells and tree cores were examined in order to track potential historic anthropogenic contamination of the water and the vegetation. The data obtained from the archeological bivalve shells show that the modern rivers yield 87Sr/86Sr ratios which are similar to those of the past. However, the tree cores registered decreasing 87Sr/86Sr values over time towards present day likely mirroring anthropogenic activities such as forest liming, coal mining and/or soil acidification. The comparison of 87Sr/86Sr of the Thuringian skeletons excavated in the same area also shows that the vegetation samples are very likely anthropogenically influenced to some extent, affecting especially 87Sr/86Sr of the shallow rooted plants.

Description: Bivalve shells are reliable bio-archives for sub-annual to multi-decadal climate reconstructions. The well-established and calibrated bivalve species 〈em〉Arctica islandica〈/em〉 is long-lived (400 yrs), abundant in the fossil record and widely distributed in the North Atlantic. The reconstruction of atmosphere-ocean phenomena, such as NAO, has been demonstrated successfully in this species. Here we present data from early Holocene (9800 cal yrs BP) 〈em〉A. islandica〈/em〉 specimens from Svalbard (78°N). All analysed specimens exhibit a dominant 11-year periodicity in their annual shell growth banding pattern. We hypothesise that this cycle is associated with insolation changes driven by the solar sunspot cycle. So far we can only hypothesize about the mechanistic link between the solar cycle and bivalve shell growth. In the high Arctic, where the summer bivalve growing season is characterised by 24 hour daylight, solar energy is the key limiting factor of plankton growth, the main food source for this species. Changes in plankton availability, as a direct result of varying solar insolation, are likely to be reflected in annual shell growth increments.

Description: Understanding past seasonal temperature variability in the ocean is essential to evaluate the effects of future climate change on marine ecosystems. Here, we estimate seasonal water temperature amplitudes from stable oxygen isotope (δ18Oshell) values of fossil shells of Arctica islandica (assuming δ18Owater = + 0.9 ± 0.1‰ V-SMOW). Specimens were collected from three Pleistocene successions (Emilian and Sicilian substages of the Calabrian) in Central and Southern Italy (i.e., Rome, Lecce and Sicily). Biostratigraphic analyses from Rome Quarry deposits indicate an age between 1.6 and 1.2 Ma, whereas Sicily and Lecce successions are slightly more recent (between 1.1 and 0.62 Ma). Prior to carbonate geochemical analysis, we checked the shells for potential diagenetic alterations (e.g., from aragonite to calcite) using confocal Raman microscopy. δ18Oshell transects indicate an annual temperature amplitude of about 3 °C during the Early Pleistocene. This is in sharp contrast to reconstructions based on faunal assemblages, according to which the simultaneous occurrence of boreal and warm-water species in the Calabrian Mediterranean Sea suggests a much higher seasonality (ca. 10 °C). The low seasonality and the relatively cold water (9–10 °C) indicate the outcrops represent colder climatic conditions compared to modern times, and suggest the occurrence of a maximum glacial phase.

Description: Future climate change will have significant effects on ecosystems worldwide and on polar regions in particular. Hence, palaeo-environmental studies focussing on the last warmer-than-today phase (i.e. the early Holocene) in higher latitudes are of particular importance to understand climate development and its potential impact in polar systems. Molluscan bivalve shells constitute suitable bio-archives for high-resolution palaeo-environmental reconstructions. Here, we present a first reconstruction of early Holocene seasonal water temperature cycle in an Arctic fjord based on stable oxygen isotope (δ18Oshell) profiles in shells of Arctica islandica (Bivalvia) from raised beach deposits in Dicksonfjorden, Svalbard, dated at 9954–9782 cal. yr BP. Reconstructed maximum and minimum bottom water temperatures for the assumed shell growth period between April and August of 15.2°C and 2.8°C imply a seasonality of about 12.4°C for the early Holocene. In comparison to modern temperatures, this indicates that average temperature declined by 6°C and seasonality narrowed by 50%. This first palaeo-environmental description of a fjord setting during the Holocene Climate Optimum at Spitsbergen exceeds most previous global estimates (+1–3°C) but confirms studies indicating an amplified effect (+4–6°C) at high northern latitudes.

Description: Shells of the bivalve Arctica islandica serve as high-resolution archive of past environmental conditions. Stable oxygen isotopes (δ18O) values from wellpreserved A. islandica shells are frequently used as a proxy for water temperature (and salinity). Hence, this species may improve distinctly our understanding of seasonal temperature dynamics in the past. We present the first stable isotope (δ18O & δ13C) analysis on a fossil semi-recrystallized A. islandica shell from the Tjörnes Beds of Iceland (Pliocene). Confocal Raman microscopy is used to identify areas of pristine aragonite and recrystallized calcite shell, which were then sampled by highresolution micro-milling. We compare paleo-water temperatures inferred from stable oxygen isotope ratios of both recrystallized and non-recrystallized portions of the shell to highlight and discuss the impacts of taphonomic alterations on a micro-scale and its implications for paleo-environmental reconstructions. Our findings emphasize the need for careful interpretation of carbonate-based water temperature reconstructions, because small-scale diagenesis can significantly modify the original stable oxygen isotope signature and substantially distort the paleoclimatic or paleoenvironmental signals inferred thereof.

Description: 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.

Description: Pronounced decadal climate oscillations are detected in a multi-centennial record based on shell growth rates of the marine bivalve mollusk, Arctica islandica, from Iceland. The corresponding analysis of patterns in sea level pressure and temperature exhibit large-scale teleconnections with North Atlantic climate quantities. We find that the record projects onto blocking situations in the northern North Atlantic. The associated circulation shows a low-pressure signature over Greenland and the Labrador Sea and a high-pressure system over Western Europe associated with northeasterly flow towards Iceland and weakening in the westerly zonal flow over Europe. It can be speculated that such circulation affects food availability controlling shell growth. On multidecadal time scales, the record show a pronounced variability linked to North Atlantic temperature. In our record, we find enhanced variability of the shell growth rates on multidecadal time scales, and it appears that this oscillation has high amplitudes in the 16th to 18th century also consistent with marine alkenone data. It is conceivable that these climate oscillations, also linked to sea ice export and enhanced blocking, are a more pronounced feature during times when the climate was relatively cold.