Description: Understanding the climate of the past and past seasonal temperature amplitudes is essential to evaluate the effects of future climate change on marine ecosystems. The Mediterranean Sea is of great importance due to its crucial role in modern atmospheric phenomena such as the North Atlantic Oscillation (NAO). Fossil shells of the bivalve Arctica islandica were collected from three different Pleistocene successions in Italy. The seasonal water temperature amplitude was reconstructed using stable oxygen isotope (δ18Oshell) analysis. Samples were derived by the micro-milling approach and measured by isotope ratio mass spectrometer. Results show a low seasonality scenario (~3°C). This is in sharp contrast to the assumption that the simultaneous occurrence of boreal and warm-water species in the middle Calabrian Mediterranean Sea can be explained by high seasonality (~10°C). A prominent 6-year cyclicity was identified in the shell growth time-series by means of spectral analysis. This signal might be linked to the NAO whose periodicity ranges between 5-9 years. However, a connection to the Mediterranean Oscillation cannot be excluded. The low seasonality (~3°C) and the relatively low mean water temperature (9-10°C) indicate that the middle Calabrian Mediterranean Sea was characterized by colder climatic conditions compared to nowadays, indicating a maximum glacial phase.

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: “Bioarchives” are organisms, which form hard parts over the course of their lifetime that remain even after the death of the organism. Environmental conditions prevailed during the lifetime of the bioarchives can be approximated from anatomical, morphological and geochemical properties on the shell. For instance, shell growth rates constitute a “proxy” of general living conditions, oxygen isotope ratios (δ18O) are an established proxy of water temperature, and shell content of heavy metals or of organic constituents can be indicative specific pollution histories. Due to their high resolution, bivalve shells are well suited for sclerochronological studies. Generally, this science focuses on growth rates and chemical properties of hard parts. The ocean quahog Arctica islandica is suited as a bioarchive due to its broad geographic distribution and longevity. This study looks at growth patterns in the shells of the bivalve A. islandica (marine) and Unio sp. (freshwater). The objective was to establish standard procedures for shell preparation to visualize shell increments formed on a daily basis (“microincrements”). In order to visualize microincrements thin-sections of the marine bivalve A. islandica and the freshwater bivalve Unio sp. were prepared. Therefore, different attempts for embedding, etching, bleaching and visualization were tested. Microincrements are visible in thin-sections of both genera. The microincrements of the freshwater mussel Unio sp. are significantly smaller (1.5 μm on average) than those of A. islandica (12.5 μm on average). However, microincrements in Unio sp. are more easily recognizable and can be measured consecutively over a range of more than one year. The visualization of microincrements in A. islandica remained more challenging and therefore additional attempts such as bleaching, etching and additional visualization techniques were tested for their potential to improve the visualization of microincrements. The visualization of microincrements in A. islandica still needs further improvement before measured microincrement widths can be correlated to environmental data. However, Unio sp. seems to have great potential and can be used as a window to reconstruct environmental data on a daily scale in the future.

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: 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.