It is important to understand the historical precedents of current situations to be able to anticipate where the current global environmental and climatic change may lead. Geo-historical data provide information beyond the limitations of instrumental data. This study aims to reconstruct components of the palaeoclimatic and palaeoenvironmental history of the Beagle Channel (BC) during the Late Holocene by using Ameghinomya antiqua shells. We use fossil and modern shells in a comparative analysis through a multiproxy approach, i.e., shell morphometrics, shell growth, and stable oxygen isotope ratios. A holistic analysis of all the proxies indicates that higher productivity occurred around 3542 yr B.P. in the BC, evidenced by more significant growth, size, and longevity in fossil specimens. In addition, smaller ligaments, cardinal teeth, and the pallial sinus in fossil specimens indicate a low-energy environment typical of a marine archipelago. Lastly, palaeotemperatures are estimated to be warmer than today, although the intensity may be overestimated due to the freshwater inflow that would change the salinity of the BC waters. Further analysis in Late-Holocene shells is essential for a more detailed environmental reconstruction around the southern tip of South America.

Bivalve sclerochronological records with annually resolved growth bands are applicable proxies in reconstructing features of the hydro-climate system. Here we evaluate the relationship between growth indices of A. islandica , previously collected at approximately 82 m depth in the North Atlantic, and seasonal subsurface temperature at various depths for the 1900–2005 period. Correlations with sea surface temperature at the collection site are not significant during winter and weak for the remaining seasons. The strongest in-phase correlations persist for summer and autumn below 56 m water depth, whereas weaker correlations are lagged by one or two years. We also observe similarities with distant water bodies in the North Atlantic sector, and a corresponding large-scale oceanographic pattern that increases significantly with water depth along the trajectory of the North Atlantic Current. We suggest that by investigating the relationship with the temperature signal at various depths locally and at large-scale increases the reliability and application of bivalve shells as marine archives.

Amiantis purpurata is a common warm-temperate water bivalve species distributed from southern Brazil to northern Patagonia, Argentina, which has a rich and well preserved fossil record in the San Matías Gulf (SMG) dating back to the late Quaternary. This study aims to establish A. purpurata shells as a new palaeoarchive of past marine conditions in South America. We compared the stable oxygen and carbon profiles (δ18Oshell; δ13Cshell) of eleven specimens of A. purpurata from different geological times (modern, Late Holocene and interglacial Late Pleistocene), and additionally present in situ oxygen isotope values of seawater within SMG (δ18Owater). Using both sets of information, we calculated and reconstructed palaeowater temperatures for the Late Holocene and compared them to modern water temperatures. Our findings indicate that A. purpurata records past environmental parameters such as water temperatures on a seasonal scale and can therefore be considered a suitable candidate for future palaeoenvironmental reconstructions in Northern Patagonia. This study is the first step towards further stable isotope analyses on fossil A. purpurata shells, which will show whether and if so, to what extent, important global climate events such as the Neoglacial (Early Holocene), the Hypsithermal (Middle Holocene) and the Little Ice Age (Late Holocene) occurred in South America.

The coastal polar and subpolar systems are particularly affected by a rapid regional climate change. Gathering hydrographic core and specific ecological data for the past 25 years at the Dallmann-Carlini station in Potter Cove (King George Island, South Shetland Islands) has proven a continuous observation to be essential for understanding the dynamic changes of marine and terrestrial ecosystems in the Northern West Antarctic Peninsula (WAP) sector. Several long-term ecological data series were analyzed to track climate change across system compartments from glaciology to community composition. It is for the first time ever that the ecological impacts of the transgression from a tidewater to an exclusively land based glacier in an Antarctic cove is documented by a multi-disciplinary research team. While focusing on the climate change related processes in the showcase area Potter Cove, expansion of the research scope to compare the local King George Island to the regional recent and late Holocene deglaciation patterns at the WAP are planed through cross station networking with USA and UK partner activities in different areas of the WAP (recent Belmont call on Biodiversity and Ecosystem Services proposal FjordBioServices) and towards the sub-Antarctic systems of Tierra del Fuego. In order to improve our understanding of climate change effects on highly dynamic and understudied areas in the Antarctic and Sub-Antarctic the SCAR community highlighted the importance of coastal observatories. Mirroring our previous multinational, interdisciplinary observations in Potter Cove, BLOOMS, we introduce to the Beagle Land and Ocean Observing and Modelling System, a multinational (Argentinian, Chilean, German, and USA) and interdisciplinary initiative to study the effects of climate change on terrestrial and marine systems. A first workshop on the implementation of an observatory, supported by Argentinian and German funds within the frame of the DynAMo project (Dynamic Effects of Climate Change and loss of ice mass on terrestrial, limnic and marine ecosystems in Patagonia, BMBF), addressed main scientific questions and discussed local stakeholder involvement. A first joint field mission is planned for austral spring 2018, and instruments are planned to be launched in 2019.

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.

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 1.2Ma, whereas Sicily and Lecce successions are slightly more recent (between 1.1 and 0.62Ma). 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.

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.

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.

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 Tjornes 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.

Biological hard parts and skeletons of aquatic organisms often archive information of past environmental conditions. Deciphering such information forms an essential contribution to our understanding of past climate conditions and thus our ability to mitigate the climatic, ecological, and social impacts of a rapidly changing environment. Several established techniques enable the visualization and reliable use of the information stored in anatomical features of such biogenic archives, i.e., its growth patterns. Here, we test whether confocal Raman microscopy (CRM) is a suitable method to reliably identify growth patterns in the commonly used archive Arctica islandica and the extinct species Pygocardia rustica (both Bivalvia). A modern A. islandica specimen from Norway has been investigated to verify the general feasibility of CRM, resulting in highly correlated standardized growth indices (r > 0.96; p < 0.0001) between CRM‐derived measurements and measurements derived from the established methods of fluorescence microscopy and Mutvei's solution staining. This demonstrates the general suitability of CRM as a method for growth pattern evaluation and cross‐dating applications. Moreover, CRM may be of particular interest for paleoenvironmental reconstructions, as it yielded superior results in the analysis of fossil shell specimens (A. islandica and P. rustica) compared to both Mutvei staining and fluorescence microscopy. CRM is a reliable and valuable tool to visualize internal growth patterns in both modern and fossil calcium carbonate shells that notably also facilitates the assessment of possible diagenetic alteration prior to geochemical analysis without geochemically compromising the sample. We strongly recommend the CRM approach for the visualization of growth patterns in fossil biogenic archives, where conventional methods fail to produce useful results.

A comprehensive understanding of past climates and environmental conditions is essential for our ability to successfully predict the likely impacts of future climate change and to effectively employ adaptation and mitigation strategies. The continued improvement and verification of numerical global circulation models (GCMs) is our best tool for predicting future climate scenarios. However, longer time-scale reconstructions particularly rely on archives (e.g., ice cores, sediment cores) that contain preserved records of past conditions (proxies) in their biogenic hard parts (e.g., shells, bones, teeth) or non-biogenic deposits/accumulations (e.g., lake varves, layers in stalagmites or ice cores). The marine bivalve Arctica islandica is one such versatile and commonly used biogenic archive. Its key advantages are its longevity (up to 500 years old), its wide distribution throughout the North Atlantic and its abundance in the fossil record (back to 20 Ma). Variability in shell growth and the biogeochemistry of its shell carbonate (aragonite) enable reconstructions of, for example, large-scale ocean-atmosphere phenomena such as the North Atlantic Oscillation and sub-annual (seasonal) absolute water temperatures (based on stable oxygen isotopes). This well understood and wellcalibrated archive has most commonly been used for environmental reconstructions in the last 2,000 years but its full potential for climate reconstructions further back in time has not yet been fully exploited. Therefore, this thesis aims to thoroughly assess the potential of sub-fossil (up to 10,000 years old) and fossil A. islandica shell specimens as a palaeo-archive that records the environmental conditions of the North Atlantic during past warm phases. The use of any proxy data from fossil specimens presents challenges that can significantly impact upon palaeo-environmental interpretations. I firstly present a new methodology using confocal Raman microscopy (CRM) as a powerful sclerochronological tool for assessing preservation and identifying taphonomic alterations in the original shell carbonate. Diagenetic modifications to the shell make it challenging to visualize the internal growth patterns and typically render the specimen unusable for biogeochemical analysis (e.g., stable isotope or trace elemental analyses). The CRM mapping approach outlined here proves that CRM leads to comparable and even superior results when compared to commonly used growth increment visualization techniques on both modern and particularly on fossil shell material (A. islandica and Pygocardia rustica; both Pliocene). I also clearly demonstrate the significant impact that the recrystallization of metastable shell aragonite to calcite can have on isotopic signatures within the shell carbonate. δ18O and δ13C signatures in recrystallized shell sections of a Pliocene A. islandica (Iceland) show tremendous changes from the pristine shell. Preservation state, which is often overlooked, therefore has a substantial impact on isotope records and serious implications for environmental and climatic interpretation. I therefore strongly emphasise the crucial need for preservation assessment prior to sampling for any proxy record and that CRM is an ideal tool with which to do this. This thesis presents a reconstruction of high latitude (Svalbard) seasonality during the last warmer-than-today phase based on the archive A. islandica. Meticulously discussing all relevant considerations (e.g., shell preservation, palaeowater depth, palaeo-water chemistry, ice volume effect, etc.), I show that seasonal temperatures in a fjord setting during the Holocene Climate Optimum (HCO) were considerably higher than today (+6°C on average), which impressively identifies past polar amplification (expected HCO global mean temperature +3°C). This presents a first indication of the possible impacts of future climate change in high latitude marine regions (IPCC, 2013 stating up to +3.7°C global temperatures until CE 2100). The further analysis of internal shell growth patterns of HCO A. islandica specimens from Svalbard detect a pronounced and significant 11-year oscillation using tools of spectral frequency analysis. Such a signal has been previously reported in other archives and has most often been associated to the 11-year solar sunspot cycle (Schwabe cycle). Solar-climate interactions remain a debated issue, as present data is temporally and spatially insufficient to decipher any hypothetical links. Therefore no previous studies propose any explanation for a mechanistic link between shell growth in biogenic marine archives and solar activity. In this thesis I propose a first possible link between solar activity and shell growth via a biological amplifying mechanism − UV radiation and phytoplankton productivity. I emphasize that the strongly simplified hypothetical explanation presented does not claim to be conclusive. It is instead a first explanation that is intended to fuel debate and discussion on this vitally important topic that has been so far overlooked. This study shows that growth and biogeochemical proxies recorded in the shells of A. islandica are a powerful archive of past climate conditions and variability on sub-annual to multi-centennial timescales. The seasonal environmental record of past warm intervals presented is a particularly valuable result, showing that northern North Atlantic shallow marine ecosystems may experience amplified warming under future global mean climate scenarios. The importance of understanding the mechanistic links between climate drivers and growth in biogenic archives cannot be underestimated and is a priority for future research. It is hoped that the methodological advances presented here will additionally lead to significant improvements in the quality of geochemical and growth increment based biogenic proxy data produced by the sclerochronological community by facilitating preservation assessment prior to any analysis.

Bivalve shells are reliable bio-archives for sub-annual to multi-decadal climate reconstructions. The well-established and calibrated bivalve species Arctica islandica 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) A. islandica 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.

Amiantis purpurata is a typical warm-temperate water species distributed from southern Brazil to northern Patagonia, Argentina. Recent and well preserved fossil specimens were recovered from San Matias Gulf in northern Patagonia. Holocene (shell age 3630 ±100 years BP) and interglacial Pleistocene (MIS 5, 100 ka years BP) marine sediments were used for a comparative analysis of stable isotopic profiles (δ18O; δ13C). The values range of Pleistocene A. purpurata was from -0,93‰ to 0,85‰ for δ18O and from -1,02‰ to 1,9‰ for δ13C. Holocene shell was from -0,34‰ to 1,13‰ for δ18O and from 1,45‰ to 2,44‰ for δ13C. And Recent shell was from -0,66‰ to 1,56‰ for δ18O and from 0,7‰ to 2,6‰ for δ13C. The δ18O values indicate warmer waters in Pleistocene compared to Holocene and Recent. The intra-annual δ18O shell temperature is higher today (Δδ18ORecent=2,22‰) compared to the Holocene (Δδ18OHolocene=1,47‰) and the Pleistocene (Δδ18OPleistocene=1,76‰). Pleistocene δ13C range value was the widest (Δδ13CPleistocene=2,92‰), but Holocene (Δδ13CHolocene=0,98‰) and Recent (Δδ13CRecent=1,9‰) values were tighter and more positive than Pleistocene. This could be explained by changes in ocean circulation since San Matias Gulf would has been formed approaching 12 ka years BP (after MIS 5, Ponce et al. 2011 Biol. J. Linn. Soc. 103, 363–379). These shells showed a clear marine environment but with a difference in sea surface temperature and ocean circulation through geological time in northern Patagonia. Our findings indicate that A. purpurata is a suitable candidate for detailed paleoenvironment reconstructions in North Patagonia. Further analyses will show whether some notable events that occurred during the Holocene, such as the Neoglacial (early Holocene), the Hypsithermal (Middle Holocene) and the Little Ice Age (Late Holocene) have been recorded in fossil A. purpurata shells.