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The Patagonian Sea in the SW Atlantic is one of the most productive marine ecosystems worldwide. Besides its economic relevance, this shelf sea serves as a major sink for atmospheric CO2 and thus plays a major role in global climate. Despite that, the marine climate dynamics in that region remain barely known. Instrumental records only cover the last 30 years or so and high-resolution climate archives are currently not available. Here, we explore the possibility to obtain seasonally to inter-annually resolved paleotemperature data from shells of the bivalve mollusk, Leukoma antiqua collected alive from the shallow subtidal zone of the San Jorge Gulf. Results demonstrate that this species grows during summer and – at least at slow rate – during winter at this locality and records nearly the full seasonal temperature amplitude (monthly averages) in the form of δ18Oshell. Furthermore, isotope-based climate reconstructions will be limited to the first 15 years of life, because growth rates are sharply reduced afterward which aggravates sampling. The oldest studied specimen attained an age of 34 years. Annual, fortnightly and lunar daily increments can potentially be used to determine the timing and rate of seasonal shell growth and help placing the shell record into precise temporal context. However, due to interferences with the shell microstructure, sub-annual growth patterns were only occasionally well developed. In this study, the temporal alignment of the growth record was therefore largely achieved by forcing Tδ18O to match the shape of the instrumental temperature curve. In some years it was possible to validate such temporal alignments with fortnight increments. Shell growth rate is strongly linked to primary production which attains a maximum in spring. For yet unexplained reasons, shell formation occurs with an offset of almost −1‰ (−0.9 ± 0.3‰) from expected oxygen isotopic equilibrium with the ambient water. When this offset is adjusted for, δ18Oshell can be used to compute past water temperature. Given the individual variability regarding δ18Oshell, it is advised to study a sufficient number coeval specimens to obtain more reliable information on the seasonal temperature range. Presumably, the overall life history and the isotopic offset is similar for L. antiqua specimens at other localities in southern South America. Since L. antiqua not only dominates modern nearshore benthic assemblages, but also occurs abundantly in Quaternary deposits along the Argentine Patagonian coast, this species can significantly contribute to a better understanding of natural baseline conditions and past climate dynamics in southern South America. Fil: Rubo, Samantha. Johannes Gutenberg Universitat Mainz; Alemania Fil: Aguirre, Marina Laura. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina Fil: Richiano, Sebastián Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico de Geología y Paleontología; Argentina Fil: Medina, Rubén Alberto. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; Argentina Fil: Schöne, Bernd R.. Johannes Gutenberg Universitat Mainz; Alemania

Trace element time-series in bivalve mollusk shells and other (biogenic) materials can potentially serve as environmental proxies. Yet, the applicability of element-to-calcium ratios is often challenging, because non-environmental factors such as vital effects distort or mask environmental signals. If a trace element time-series is driven by an environmental factor, it should be reproducible within and between coeval specimens of the same species. In the present study, we tested whether time-series of trace element-to-calcium ratios can be reproduced within and between coeval specimens of the bivalve Arctica islandica and thus whether an external signal is encoded in the temporal variations of trace elements along the shells. We determined the concentration of sodium, magnesium, manganese, strontium and barium by means of LA-ICP-MS in line scan mode in the hinge area of seven specimens from the Isle of Man, the Gulf of Maine and Iceland. In each specimen, the element composition was determined along two replicate line scans to gauge intra-specimen reproducibility. The degree to which trace element time-series can be reproduced was inferred from linear regression analysis and equaled on average 95 ± 4% for Ba/Ca, 82 ± 27% for Mg/Ca, 83 ± 18% for Sr/Ca, 74 ± 23% for Mn/Ca, and 22 ± 4% for Na/Ca ratios (values correspond to coefficients of determination of the linear regression analysis expressed in percent). The synchrony of Ba/Ca time-series between contemporaneous specimens from the same habitat has already been demonstrated in previous studies. Here, we observed common high-frequency variations (i.e., peaks) among coeval A. islandica from the same site for Mg/Ca, Sr/Ca, Mn/Ca and Na/Ca ratios, especially among specimens of similar ontogenetic age and with similar shell growth patterns. The results of the present study should be considered in interpretations of trace element time-series in bivalve shells as they can help to improve environmental and climate reconstructions.

Stable isotope signatures of bivalve shells serve as important paleoclimate proxies. However, such data can be biased as a consequence of physical and chemical sample pretreatment and contamination during sampling. As yet, the potential isotope error induced by paleontological preservation techniques and specific methods used in bivalve sclerochronology have not been systematically assessed. To address these issues, homogenized powder of a well-preserved, aragonitic fossil shell, Glycymeris obovata (ca. 30 Ma old) as well as Carrara marble powder (calcite) were exposed to ultrasound, a set of different staining solutions and cleaning agents. In addition, these reference materials were artificially contaminated with increasing proportions of powder prepared from periostracum, Alcian Blue and cured adhesives. Whereas some treatments (rinsing with Milli-Q water, immersion in Alizarin Red S solution and possibly Mutvei's solution) did not affect the isotope values of the carbonate samples, severe isotope shifts were observed after immersing shell powder in Feigl's solution (Δδ 18 O = − 0.62‰) and mixing Carrara marble powder with Gluetec Metal Epoxy (a contamination level of 41.7 wt% shifted δ 18 O and δ 13 C values by − 2.12‰ and − 1.74‰, respectively). Increasing levels of Metal Epoxy in the sample resulted in a sharp, non-linear decrease of the isotope values. The majority of tested treatments conducted with the carbonate powders and contaminants added to them caused minor to moderate, mainly statistically significant isotope offsets (bleaching with NaOCl and H 2 O 2 ; exposure to ethyl alcohol and Rewoquat W 3690 PG, a surfactant; ultrasonic cleaning; contamination with powder of Alcian Blue, cured superglue, several different polyepoxies, methacrylates and polyvinyl butyral resins as well as periostracum). In conclusion, pretreatment of bivalve shells with an intended use for isotope analysis should be kept at an absolute minimum and contamination with adhesives etc. should be avoided. Specimens from museum collections that underwent special conservation methods may be of limited value for isotope studies, unless the history of sample treatment is known. Although only a few of the tested substances and methods strongly biased the isotope signatures, even small changes can accumulate to levels that are inacceptable for high-resolution paleoclimatology.

Understanding environmental conditions faced by hunter-fisher-gatherers during the Pleistocene and Holocene, and interpretation of subsistence strategies, social organisation and settlement patterns, are key topics for the study of past human societies. In this respect, oxygen isotope values (?18O) of mollusc shell calcium carbonate can provide important information on palaeoclimate and the seasonality of shell collection at archaeological sites. In this paper, we tested P. vulgata shells from northern Iberia as a paleoclimate archive through the study of shell oxygen isotope values and sclerochronology of modern samples. Results showed that limpets formed their shells close to isotopic equilibrium, with an average offset between measured and predicted values of 0.36?. This offset is significantly reduced with respect to those reported in previous studies, probably due to the use of highly resolved data on the isotopic composition of the water when calculating predicted values. Despite large intra-specific variability, shell growth patterns of P. vulgata revealed a common pattern of higher growth in spring and a growth cessation/slowdown in summer and winter. The seasonal growth cessation/slowdown did not exceed three months. Therefore, a correct interpretation of the season of shell collection is still possible. Reconstructed seawater temperature exhibited a high correlation with instrumental temperature (R2 =0.68 to 0.93; p b 0.0001). Despite periods of growth cessation/slowdown, mean seawater temperatures and annual ranges were reconstructed accurately. As demonstrated here, seawater temperature can be reconstructed with a maximum uncertainty of ±2.7 °C. Therefore, our study shows that oxygen isotope values from P. vulgate can be used for the reconstruction of paleoclimate and the season of shell collection This research was part of the projects NF100413 (Newton International Fellowship granted to IGZ) and HAR2013-46802-P (funded bythe Spanish Ministry of Economy and Competitiveness, MINECO).

This study presents the first stable isotopic and sclerochronological calibration of the bivalve Anomalocardia flexuosa (Linnaeus, 1767) in relation to environmental variables in a subtropical coastal area of southern Brazil. We investigate incremental shell growth patterns and δ18O and δ13C values of modern specimens collected alive from the Laguna Lagoonal System (LLS). Shells of Anomalocardia flexuosa are also one of the main biological components of pre-Columbian archaeological shell mounds and middens distributed along the Brazilian coastline. We therefore selected archaeological specimens from a local late Holocene shell mound (Cabecuda) to compare their stable carbon and oxygen isotope values with those of modern specimens. Shell growth increments, δ18O and δ13C values respond to a complex of environmental conditions, involving, for example, the effects of temperature and salinity. The isotopic information extracted from archaeological specimens from Cabecuda shell midden in the LLS indirectly indicates that environmental conditions during the late Holocene were different from present day. In particular, intra-shell δ18O and δ13C values of archaeological shells reveal a stronger marine influence at 3 ka cal BP, which is in contrast to the seasonal freshwater/seawater balance that currently prevails at the LLS.

Geochemical signatures from biogenic carbonates are being increasingly employed as palaeoenvironmental proxies. In turn, many of these proxy archives including mollusc shells, corals, and otoliths have periodic growth structures, which allow the reconstruction of chronologically constrained records of palaeoenvironmental variability at unparalleled high temporal resolution. Studying the growth and chemistry of these periodic growth structures is known as sclerochronology. Biogenic hard parts accumulate in geological or archaeological deposits, and can be directly dated using radiometric and racemisation methods. They therefore offer the opportunity for high-resolution palaeoenvironmental reconstructions across many time intervals, all over the globe. Such data are important for several reasons: (1) understanding past climate and environmental change provides a means of contextualising current and future climate change and ecological disturbance; (2) high-resolution palaeoenvironmental records are essential for constraining, testing and validating global and regional numerical climate models; (3) palaeoenvironmental records from biogenic carbonates can provide an environmental framework from which to understand the behavioural changes and interactions of peoples with their environment. However, inter and intra-species differences in growth rate, physiology, and environmental response can cause variations in the chemical profiles of biogenic carbonates. Before geochemical data is employed for palaeoenvironmental reconstructions, it is thus necessary to examine modern specimens of the target species, or related taxa, to understand how geochemical variations are influenced by local environmental conditions, kinetic and vital effects. This allows the generation of quantitative and more reliable proxy records of environmental change. This special issue brings together the latest research on palaeoenvironmental proxy development and validation in biogenic carbonates. It includes studies on marine, freshwater and estuarine organisms (molluscs, corals and echinoderms), and on traditional as well as novel geochemical proxies. The papers presented here include in situ field calibration studies, laboratory growth experiments as well as methodological studies into the effects of sampling and pre-treatment. The geographical scope is broad, encompassing both the northern and southern hemispheres including South Africa, South America, Australia, Asia, the Mediterranean Sea and the North Atlantic.

Aquatic eutrophication is becoming a serious environmental problem throughout the world. The utility of bivalves as bio-filters to improve water quality and reduce algal blooms has been widely acknowledged, but the potential usefulness of bivalve shells as retrospective monitors of eutrophication-induced environmental change has received little attention. Here, we present the first multi-year, high-resolution Mn/Ca shell records of the freshwater mussel, Hyriopsis cumingii (Lea, 1852) from a shallow eutrophic lake (Lake Taihu, China). Mn/Ca shell time-series of the two studied shells exhibit a high degree of synchrony after being placed in a precise temporal context by means of growth pattern analysis. There is a large inter-annual variability of Mn/Ca shell records during 2011–2015, with the highest value occurring in 2013. Mn/Ca shell also displays a pronounced intra-annual variability with maxima consistently occurring during late spring/early summer. The high reproducibility of Mn/Ca shell time-series among contemporaneous specimens highlights the existence of strong environmental rather than biological control on the incorporation of Mn into the shells. In particular, the striking feature of late spring/early summertime Mn/Ca shell maxima is synchronous with the occurrence of reducing conditions beneath the sediment-water interface (SWI). The latter results in substantial increases of biologically available Mn 2 + in the sediment pore water and organic particles, the element being rapidly taken up from these sources by the mussels with subsequent incorporation of Mn into their shells. Therefore, Mn/Ca shell can potentially serve as a high-resolution proxy of the mobility of Mn at the SWI. As demonstrated by the present study, documenting and understanding geochemical properties of bivalve shells can help to retrospectively monitor eutrophication-induced environmental change in aquatic ecosystems.

Limpet shells are common components of many archaeological sites in the Mediterranean. To test whether δ18O values from archaeological Patella caerulea shells can serve as a reliable palaeothermometer for the Mediterranean and a reliable archive of season of collection information, we collected live P. caerulea from eight Mediterranean locations in Croatia, Israel, Libya, Malta, Tunisia, and Turkey. Shell growth patterns were studied in section, and samples for oxygen isotope analysis were milled from the shells and used to calculate sea surface temperature (SST). As with other species of limpet, SST reconstructed from P. caerulea δ18O values were lower than expected from observational records. However, when a correction factor of − 0.72‰ was applied, the shells recorded SST within the range of instrumental SST. SST calculated from δ18Oshell values of the most recently formed shell portion of monthly-collected shells from one site in Libya were strongly and significantly correlated with instrumental SST in the region (R2 = 0.95). Oxygen isotope curves from individual shells sampled at high resolution from each of the study sites across the Mediterranean exhibited sinusoidal patterns. Annual growth lines correlated with the lowest δ18Oshell values and were thus formed in summer. However, shell growth rates varied markedly between the sites. Some sites with larger shells recorded less than a year of growth in broad, highly irregularly shaped increments. At other sites, medium sized shells recorded several years of growth with clear, regular growth increments. A sclerochronological approach can therefore be used to pre-screen limpet shell sections before geochemical sampling. The δ18Oshell values from shells sampled at high-resolution recorded the full seasonal range of instrumental SST at each collection site. This reinforces the potential of this species as one of the few sub-seasonal resolution palaeoenvironmental archives in the region. Additionally, the pattern of δ18Oshell variation from the last formed shell portion was studied to determine whether accurate season of collection information could be identified from P. caerulea shells. The correct season was interpreted > 80% of the time indicating that this species is a good candidate for seasonal shellfish foraging studies using archaeological shells.

New sclerochronological data suggest that a variability comparable to the North Atlantic Oscillation (NAO) was already present during the middle Oligocene, about 20 Myr earlier than formerly assumed. Annual increment width data of long-lived marine bivalves of Oligocene (30–25 Ma) strata from Central Europe revealed a distinct quasi-decadal climate variability modulated on 2–12 (mainly 3–7) year cycles. As in many other modern bivalves, these periodic changes in shell growth were most likely related to changes in primary productivity, which in turn, were coupled to atmospheric circulation patterns. Stable carbon isotope values of the shells (δ 13 C shell ) further corroborated the link between shell growth and food availability. Sub-decal oscillations in the 3–7 year band in other annually resolved fossil archives were often interpreted as El Nino-Southern Oscillation (ENSO) cycles. This possibility is discussed in the present study. However, combined shell-derived proxy and numerical climate model data lend support to the interpretation of a NAO-like variability. According to numerical climate models, winter sea-level pressure (wSLP) and precipitation rate (wPR) across Central Europe during the Oligocene exhibited a pattern similar to the modern NAO. The simulated NAO index for the Oligocene shows periodicities coherent with those revealed by the proxy data (2.5–6 years), yet, on shorter wavelengths than the modern NAO (biennial and 6–10 year cycles). Likely, the different paleogeography and elevated atmospheric CO 2 concentrations not only influenced the sea-level pressure pattern, but also the temporal variability of the NAO precursor. The present study represents the first attempt to characterize the inter-annual climate variability in Central Europe during the Oligocene and sets the basis for future studies on the early phase of the Cenozoic icehouse climate state.

Because the instrumental record is short and does not extend to periods before the initiation of significant human impacts, full understanding of the processes and dynamics involved in the modern phase of very rapid global change depends on the interpretation of high resolution and precisely dated proxy archives. The identification of very long-lived species of bivalve mollusc in the extratropical marine environment has been a crucial recent advance. These molluscs form patterns of periodic (usually annual) banding in their shells that are synchronous within populations, so that long (centennial and millennial) stacked chronologies can be built by crossdating from live collected to fossil shells. The variable growth rates and precisely dated geochemical data from the shell material provide long term real world data that can in principle be used to constrain climate models and to define long baselines for environmental monitoring. However, the signals in these data usually result from the complex interaction of multiple influences, and the deconvolution and understanding of these influences is a major target of the scientific field of sclerochronology. This special issue presents some of the latest research into the sclerochronology of mollusc shells. It includes contributions to our understanding of shell growth, including the identification of endogenous (non-environmental) growth rhythms that persist throughout ontogeny, and analysis in two papers of variability through ontogeny in the season of growth and the implications of such variability for temperature reconstruction. One paper presents a new network of bivalve chronologies for UK waters, with a 200-year seawater temperature reconstruction. Three papers cover trace element geochemistry, including a novel approach to sampling for LA-ICP-MS that enables giant clam shells to be sampled at daily resolution, an attempt to identify an independent temperature proxy for coastal waters using limpet shells, and a detailed study of the drivers of variability in Sr/Ca and Ba/Ca ratios. One study looks at shell microstructure as a temperature proxy, finding a coherent temperature response in the shape of the prisms.

Trace elements of bivalve shells can potentially serve as proxies of environmental change. However, to reconstruct past environments using the geochemical properties of the shells and determine the degree to which the element levels are biologically influenced, it is essential to experimentally determine the relationship between environmental variables and the element composition of the shells. To disentangle possible controls on the incorporation of strontium and barium into freshwater bivalve shells, we conducted controlled laboratory experiments using the extremely salinity and temperature tolerant Asian clam, Corbicula fluminea as a model species. Bivalves were reared for five weeks in two sets of experiments: (1) combinations of different water temperature (10, 16 and 22 °C) and food levels (0.2, 2, 4 and 8 × 104 cells/ml) with constant Sr/Cawater (2.45 mmol/mol) and Ba/Cawater (367 μmol/mol) levels; and (2) combinations of different water temperature (10, 16 and 22 °C) and different Sr/Cawater (ca. 4, 8 and 12 mmol/mol) and Ba/Cawater levels (ca. 600, 1150 and 1500 μmol/mol) with constant food level (4 × 104 cells/ml). The Sr/Cashell ratio of C. fluminea exhibited a statistically significant negative correlation with temperature and a positive correlation to Sr/Cawater, but was not affected by changing food level or shell growth rate. On the contrary, Ba/Cashell was influenced by a complexly intertwined set of variables including temperature, food level, Ba/Cawater and shell growth rate. Partition coefficients of KDSr/Ca (0.19 to 0.29) and KDBa/Ca (0.03 to 0.19) confirmed the control of vital effects over strontium and barium incorporation into the shells. As indicated by the findings, Sr/Cashell of C. fluminea from freshwater environments can serve as a reliable proxy for past water temperature if the spatiotemporal variability of strontium-to-calcium in the water is small, well-known or can be estimated from other proxies. Interpreting Ba/Cashell values, however, is much more challenging because they are controlled by a large number of environmental and physiological variables. Sr/Cashell and Ba/Cashell of C. fluminea specimens from estuarine settings in which element-to-calcium ratios are more conservative and stable can potentially function as paleoenvironmental proxies. Findings of this study can be useful to better understand the element incorporation into shells of other bivalves including marine species.

Ba/Ca shell time-series of marine bivalves typically show flat background levels which are interrupted by erratic sharp peaks. Evidence from the literature indicates that background Ba/Ca shell ratios broadly reflect salinity conditions. However, the causes for the Ba/Ca shell peaks are still controversial and widely debated although many researchers link these changes to primary productivity, freshwater input or spawning events. The most striking feature is that the Ba/Ca shell peaks are highly synchronous in contemporaneous specimens from the same population. For the first time, we studied Ba/Ca shell in mature and ontogenetically old (up to 251 year-old) specimens of the long-lived Arctica islandica . Also, we analyzed specimens from surface water and deeper water. The typical pattern of low background and erratic peaks persisted throughout ontogeny. However, due to decreasing sampling resolution and greater time-averaging in older, slower growing shell portions, the background Ba/Ca shell values appeared to gradually increase with ontogenetic age, whereas the peaks became attenuated and broader. Despite that, Ba/Ca shell maxima were still highly synchronous among contemporaneous specimens from the same locality and habitat confirming previous reports from short-lived species. Computing of annual Ba/Ca shell averages largely eliminated any bias introduced by time-averaging and sampling resolution. Strongly elevated annual Ba/Ca shell peaks in specimens from surface waters (Iceland, Faroe Islands, Isle of Man) during the 1980s appear to coincide with an extreme primary productivity pulse recorded by remote sensing. However, due to the lack of in vivo experiments, we cannot ultimately test a causal link between annual Ba/Ca shell excursions and primary productivity. We propose that Ba/Ca shell time-series, specifically the highly synchronous Ba/Ca shell peaks and annual Ba/Ca shell values in contemporaneous specimens from the same locality can serve as a tool to verify crossdating and facilitate the construction of statistically robust growth increment width master chronologies. Long-term environmental reconstructions based on bivalve shell growth chronologies can likely greatly benefit from this new technique.

The knowledge of seasonal temperature variability in the ocean is essential for understanding climate and its response to forcing factors. Time intervals with highly dynamic climate and increased seasonal forcing such as the early Holocene are of particular interest. Yet, the temporal resolution of most existing climate records is not sufficient to reconstruct temperature seasonality. Here, we present the first seasonally resolved, early Holocene, bottom-water temperature record from the Viking Bank in the northern North Sea. The reconstruction is based on the stable oxygen isotope data (δ18Oshell) of two crossdated, radiocarbon-dated subfossil shells of Arctica islandica (Bivalvia). Oxygen isotope data were combined into a 21-year long record, dated at 9593–9573 (±55) cal yr BP The record indicates an early Holocene seasonal temperature amplitude up to ca. 4.5 °C. To estimate changes in the mean state and seasonality of temperature conditions between the present and early Holocene, the record and temperatures inferred thereof are compared with modern δ18Oshell profiles and instrumental temperature data. The results indicate that the seasonal amplitude of δ18Oshell signal in the subfossil shells reflects sea-level changes. The reconstruction suggests that the long-term average and seasonal variability of temperature were similar to modern times when considering changes in the relative sea level. Our data also confirm that δ18Oshell records are reproducible and track seasonal amplitude of bottom-water temperature variability, thus demonstrate the potential for application in reconstructions of past seasonality. Furthermore, our results show that δ18Oshell records can be used to reconstruct seasonal stratification dynamics. This novel application of sclerochronological data has the potential to be used to validate and constrain paleotidal models. publishedVersion

High-resolution stable isotope data (δ18O, δ13C) were used to study growth strategies of the bivalve Venus verrucosa collected from three sites of the eastern coast of the Adriatic Sea. The principal objectives of this study were to identify the main growing season and to evaluate the potential applicability of δ18Oshell values to reconstruct the seasonal temperature variability. Calcium carbonate for oxygen and carbon isotope analyses was obtained by drilling the outer shell layer. Temporal and spatial variations in temperature and salinity values at the study sites were simulated using the 3D numerical ocean model ROMS. Annual periodicity of growth patterns was confirmed by δ18Oshell cycles which corresponded to the number of observed seasonal growth marks. Temporal alignment of stable oxygen data with modelled seawater temperature data indicates that V. verrucosa deposits shell material from March/April to December. Shell growth slowdown and/or cessation occurred between late winter and early spring when the seawater temperature dropped below 12 °C at the two northern sites, Istria and Pag Bay, and below 13 °C at the southern site, Kastela Bay. Summer temperatures reconstructed from V. verrucosa agreed well with modelled summer temperatures, but lowest reconstructed temperatures were consistently higher than the modelled winter values. The range of δ18Oshell values obtained from V. verrucosa shells is higher than the range obtained previously from other species in the eastern Adriatic Sea, indicating the high potential of V. verrucosa for temperature reconstructions.

The North Atlantic Ocean and adjacent shelf seas play a crucial role in global climate. To better constrain long-term natural variability and marine-terrestrial linkages in this region, a network of highly resolved marine archives from the open ocean and continental shelves is needed. In recent decades, bivalve sclerochronology has emerged as a field providing such records from the mid- to high latitudes. In May 2014, dead valves and young live specimens of the bivalve Glycymeris glycymeris were collected at St Kilda, Scotland. A floating chronology spanning 187 years was constructed with fossil shells and radiocarbon dated to 3910–3340 cal yr before present (BP), with a probability density cluster at ca. 3700–3500 cal yr BP. Sub-annual δ18O data were obtained from five fossil and three modern specimens and showed a strong seasonal signal in both time intervals. The growth season of G. glycymeris at this location today lasts from May to October, with most growth occurring before the temperature peak in August. Thus, the modern specimens and the fossil chronology represent late-spring and summer sea surface temperatures (SST). The annual temperature range was 4.4 °C in the fossil shells, which is similar to the range observed today (3.8 °C). Average SSTs reconstructed from the fossil shells were 1 °C cooler than in 2003–2013 CE and similar to the early 20th century CE. The radiocarbon age of the floating chronology coincides with a climatic shift to wetter conditions on the British Isles and with a cold interval observed in palaeoceanographic records from south of Iceland. However, our data do not provide evidence of a cold interval on the Scottish shelf. The similarity in growth season and temperature range between the fossil and modern specimens are attributed to similar boundary conditions in the fourth millennium BP compared to today.

The δ18O record of well-preserved shells of the inoceramid Inoceramus hercules from the Upohlavy working quarry (Czech Republic) provides an insight into the climate variability in the late Turonian benthic environment of the Bohemian Cretaceous Basin. Similar to modern bivalves, this inoceramid species built its shell near equilibrium with the oxygen isotope value of the ambient water. Due to the nearly year-round shell growth, sequentially sampled δ18O values allowed to estimate the narrowest sub-annual temperatures fluctuations that prevailed during lifetime of the organisms. In accordance with previous studies, reconstructed temperatures suggest colder water conditions (19.0 ± 0.9 °C) during the earliest late Turonian (coinciding with the Hyphantoceras Event; also known as Hitch Wood Event) than during the later part of the substage (20.9 ± 1.1 °C). Climate warming, however, did not affect the sub-annual temperature fluctuations evenly, but predominantly affected the warmest part of the year (at least +4.0 °C). On the contrary, the coldest recorded temperatures remained more or less invariant, varying not (much) more than +1.0 °C across the studied time interval. The observed changes in the benthic temperature estimates likely reflect shifts in seasonal sea surface temperature amplitudes in response to climate forcing. Given the widespread distribution of I. hercules in the upper Turonian–lower Coniacian hemipelagic strata of Europe, the present study sets the basis for future continent-wide sub-annually-resolved climate reconstructions.

CO2-induced global warming will affect seasonal to decadal temperature patterns. Expected changes will be particularly strong in extratropical regions where temperatures will increase at faster rates than at lower latitudes. Despite that, it is still poorly constrained how precisely short-term climate dynamics will change in a generally warmer world, particularly in nearshore surface waters in the extratropics, i.e., the ecologically most productive regions of the ocean on which many human societies depend. Specifically, a detailed knowledge of the relationship between pCO2 and seasonal SST is crucial to understand interactions between the ocean and the atmosphere. In the present investigation, we have studied for the first time how rising atmospheric pCO2 levels forced surface temperature changes in Central Europe (paleolatitude ~45 °N) during the mid-Oligocene (fromca. 31 to 25Ma), a time interval of Earth history during which global conditions were comparable to those predicted for the next few centuries. For this purpose, we computed numerical climate models for the Oligocene (winter, summer, annual average) assuming an atmospheric carbon dioxide rise from 400 to 560 ppm (current level to two times pre-industrial levels, PAL) and from 400 to 840 ppm (= three times PAL), respectively. These models were compared to seasonally resolved sea surface temperatures (SST) reconstructed from δ18O values of fossil bivalve shells (Glycymeris planicostalis, G. obovata, Palliolum pictum, Arctica islandica and Isognomon maxillata sandbergeri) and shark teeth (Carcharias cuspidata, C. acutissimaand Physogaleus latus) collected fromthe shallow water deposits of the Mainz and Kassel Basins (Germany). Multi-taxon oxygen isotope-based reconstructions suggest a gradual rise of temperatures in surface waters (upper 30 to 40m), on average, by asmuch as 4 °C during the Rupelian stage followed by a 4 °C cooling during the Chattian stage. Seasonal temperature amplitudes increased by ca. 2 °C during the warmest time interval of the Rupelian stage,withwarming beingmore pronounced during summer (5 °C) than during winter (3 °C). According to numerical climate simulations, the warming of surface waters during the early Oligocene required a CO2 increase by at least 160 ppm, i.e., 400 ppm to 560 ppm. Given that atmospheric carbon dioxide levels predicted for the near future will likely exceed this value significantly, the Early Oligocene warming gives a hint of the possible future climate in Central Europe under elevated CO2 levels.

Inoceramid prisms are among the most common microfossils that can be found in Late Cretaceous strata. Since these biomineral units were formed by sequential accretion in the outer shell layer of the bivalves, they potentially serve as archives of short-term (circa-annual) paleowater temperature fluctuations. In the present study, we tested to what extent intra-prismatic stable isotope variations of individual inoceramid prisms reflect sub-annual δ13C and the δ18O patterns. We obtained multiple carbonate samples from prisms recovered from the sediment and from a cross-sectioned inoceramid shell fragment and compared data from these samples to data from classical sclerochronological sampling (i.e., sequential drilling). The analyzed shell material belonged to the species Platyceramus platinus from the Smoky Hill Chalk Member (Niobrara Formation, Kansas, USA). Scanning electron microscopy (SEM) was used to evaluate the diagenetic alteration of the studied prisms and allowed to identify suitable material for stable isotope analyses. The δ18O values of drilled carbonate samples (δ18ODrill) and of prisms (δ18OIP) compare very well to each other when temporally aligned (R2 = 0.98). The stable carbon isotope values (δ13CDrill; δ13CIP), however, show less agreement (R2 = 0.28), which is likely attributable to different time-averaging of the samples. We discuss how to identify the most suitable prisms for sub-annual paleotemperature reconstructions from disarticulated material using microgrowth patterns and geometrical features of the prisms as proxies for changing growth rates. Finally, we apply the novel sampling strategy to naturally occurring disarticulated prisms from the sediment and compare their intra-prismatic isotope values (δ13CIPS and δ18OIPS) to those of bulk-analyzed prism fragments from the sediment (δ13CBPS and δ18OBPS). Sclerochronological analysis of the prisms from the sediment yields δ18OIPS fluctuations of 1.89‰, virtually identical to the δ18OIP chronologies of the prisms extracted from the shell cross-section (1.90‰). The overall ranges of the δ18OIP and δ18OIPS values are identical (2.60‰) and capture very well the expected seasonal stable oxygen isotope oscillation derived from the δ18ODrill values (2.61‰). The range of the δ18OIPS data is two-fold larger than that of the δ18OBPS values (1.19‰), suggesting a strong effect of time-averaging on the stable oxygen isotope data of the bulk-analyzed prisms fragments. According to our novel statistical model, the resolution of δ18OBPS data can be increased by preferentially analyzing short (ca. 300 μm) individual prisms fragments (at least n = 20).

Absolutely dated, annually resolved sea surface temperature records from middle to higher latitudes covering long time intervals are crucial to better understand the climate system. Such data can potentially be obtained from variations in shell growth of long-lived bivalves such as Arctica islandica. This study presents the first statistically robust 178-yr long composite chronology (covering 1835–2012) based on sixteen live-collected and subfossil specimens of A. islandica from unpolluted, shallow waters of Northeast Iceland. Between 1875 and 1996, up to 43% of the variation in annual shell growth was explained by SST during February to September. Faster growth occurred when temperatures were warmer and food supply was elevated. However, the correlation was subject to strong temporal variations. Likewise, the inter-series correlation (synchrony among time series) was intermittently stronger and weaker. If more uniform environmental conditions prevailed over a longer time interval and the habitat was solely influenced by one of the major currents in this region – the warm, nutrient-rich Irminger Current or the cold, nutrient-poor East Iceland Current – the agreement between growth records of contemporaneous specimens broke down and the correlation between shell growth and SST was at minimum. However, when the habitat was under the alternating influence of both currents, the inter-annual variability of shell growth and synchrony in growth among the specimens were at maximum, and the correlation between SST and shell growth strengthened. As demonstrated here, the relationship between shell growth of A. islandica and environmental variables is highly complex and depends on oceanographic parameters. These findings should be taken into account in subsequent studies in order to reliably reconstruct SST and other environmental variables from shells of this species.

Incremental δ 18 O and δ 13 C signals were obtained from three well-preserved specimens of Cylindroteuthis puzosiana and from three well-preserved specimens of Gryphaea ( Bilobissa ) dilobotes from the Peterborough Member of the Oxford Clay Formation (Cambridgeshire, England). Through-ontogeny (sclerochronological) δ 18 O data from G. ( B. ) dilobotes appear to faithfully record seasonal temperature variations in benthic Callovian waters of the study area, which range from c . 14 °C to c . 17 °C (arithmetic mean temperature c . 15 °C). Water depth is estimated to have been in the region of c . 50 m, based upon comparisons between these data, previously published non-incremental sea surface δ 18 O values, and a modern analogue situation. Productivity in Callovian waters was comparable with that in modern seas, based upon δ 13 C data from G. ( B. ) dilobotes , with 13 C depletion occurring during warmer periods, possibly related to an interaction between plankton blooms and intra-annual variations in mixing across a thermocline. Incremental δ 18 O data from C. puzosiana provide temperature minima of c . 11 °C for all specimens but with maxima varying between c . 14 °C and c . 16 °C for different individuals (arithmetic mean values c . 13 °C). Temperatures for late ontogeny, when the C. puzosiana individuals must have been living close to the study site and hence the analysed specimens of G. ( B .) dilobotes , are closely comparable to those indicated by the latter. However, for significant portions of ontogeny C. puzosiana experienced temperatures between c . 2 °C and c . 3 °C cooler than the winter minimum as recorded by co-occurring G. ( B. ) dilobotes . Comparisons with modern seas suggest that descent to a depth of c . 1000 m would be necessary to explain such cool minimum temperatures. This can be discounted due to the lack of deep waters locally and due to estimates of the depth tolerance of belemnites. The most likely cause of cool δ 18 O signals from C. puzosiana is a cosmopolitan lifestyle including migration to more northerly latitudes. Mean δ 13 C values from C. puzosiana are comparable with those from G. ( B. ) dilobotes . However, the incrementally acquired data are highly variable and probably influenced by metabolic effects. The probable identification of migratory behaviour in C. puzosiana calls into question the reliability of some belemnite species as place-specific palaeoenvironmental archives and highlights the benefits of adopting a sclerochronological approach.

Sr/Ca, Mg/Ca and Ba/Ca values are heterogeneously distributed in shells of Arctica islandica. These patterns are largely associated with crystal fabrics (size, habit and orientation of crystals) or the processes controlling them. The outer sublayer of the outer shell layer (oOSL; homogenous and irregular simple prismatic crystal fabrics,) contained element/Ca values up to 62% higher than the inner sublayer (iOSL; crossed-acicular, crossed-lamellar, fine crossed-lamellar and irregular simple prismatic crystal fabrics). A gradual decrease in Sr/Ca and Mg/Ca values was observed from the outer portions of the oOSL toward the oOSL/iOSL transition zone. This chemical shift was accompanied by a gradual transition from homogenous crystal fabrics into crossed-lamellar/acicular crystal fabrics. Near annual growth lines (irregular simple prisms), i.e., during periods of slow growth, Sr and Mg seemed to be deposited in equilibrium with the ambient environment because the Sr/Ca and Mg/Ca values approached values typical for seawater. During the remainder of the growing season, Sr/Ca and Mg/Ca remained far below values expected for thermodynamic equilibrium. Ba/Ca peaks, however, occurred erratically at different times of the year without any noticeable changes in crystal fabrics. Likely, the environmental information contained in these peaks was less severely filtered by vital effects than in Sr and Mg. The findings of the present study can help to develop new techniques with which extract environmental signals from the metal-to-calcium ratios of bivalve shells.

High-resolution proxy archives from aquatic settings are essential to better understand processes and mechanisms of global change. During the last decade, it has become increasingly evident that calcified tissues of bivalve mollusks and cold-water corals, in particular, can significantly increase our knowledge of seasonal to multi-decadal paleoclimate and paleoenvironmental variability in the extratropical oceans and coastal marine settings. Daily, tidal, fortnightly and annual growth patterns of periodically formed skeletal hard parts provide a means to place the proxy record in a precise temporal context. Their extreme longevity coupled with the running similarity between growth increment time-series of contemporaneous bivalves opens the possibility of constructing stacked chronologies covering centuries to millennia which provide information on decadal climate and environmental variability and magnitudes of climate variability through time. A current major research focus is on how to translate geochemical properties of the skeletons into quantifiable environmental proxy data and how to eliminate the adverse influence of vital effects on the proxy records. This special issue presents the most recent advances in the field of sclerochronology, specifically calcified tissues of bivalve mollusks, cold-water corals and tropical shallow water corals. The majority of the contributions deal with the potential reconstruction of temperature, pH and productivity through the analysis of variable growth rates, Sr/Ca, Mg/Ca, Ba/Ca, U/Ca, Li/Ca, δ13C, δ18O and δ44/40Ca. Four papers present composite chronologies of two long-lived bivalve species and discuss inherent decadal climate variability, and one study demonstrates that sclerochronology can shed light on socioeconomic patterns of past human populations as well as resource use and resource management by people.

Due to the lack of suitable high-resolution archives, regional and continental-scale climate dynamics of southern South America are not well understood. Shells of the long-lived, shallow-marine bivalve mollusk, Eurhomalea exalbida (Dillwyn), are likely to contain information on the past water temperatures. As yet, however, no rigorous calibration study has been presented so that growth history traits and the reliability of shell oxygen isotope-based temperature estimates remain unknown. Shell growth patterns and oxygen isotope ratios of four young specimens of E. exalbida from the Falkland Islands (Southwest Atlantic) were analyzed and cross-calibrated with environmental parameters. Results indicate that E. exalbida likely captured the full seasonal temperature amplitude in its shell. Annual growth line formation occurred between fall and early winter. The most remarkable finding, however, was that E. exalbida formed its shell with an offset of − 0.48 to − 1.91‰ from expected oxygen isotopic equilibrium with the ambient water. If this remained unnoticed, paleotemperature estimates would overestimate actual water temperatures by 2.1–8.3 °C. With increasing ontogenetic age, the discrepancy between measured and reconstructed temperatures increases exponentially, irrespective of the seasonally varying shell growth rates. We attribute this finding to a pH increase in the extrapallial fluid during ontogeny favoring a dominance of the (isotopically lighter) carbonate ions over (isotopically heavier) bicarbonate ions. When this disequilibrium fractionation effect is taken into account, E. exalbida can serve as a high-resolution paleoclimate archive for mid to high latitudes of southern South America providing quantifiable temperature estimates, even from single fossil specimens.

article i nfo In this study, we use subannually resolved oxygen isotope values of fossil (dead-collected) and modern (live- caught) bivalve shells (Arctica islandica L.) from the northwestern Atlantic (Gulf of Maine, USA) to reconstruct past seasonal changes in seawater temperature. Our results indicate decreased seasonal temperature amplitude of about 1.6 °C (or ∼21%) during Medieval times (ca. AD 1033-1062) compared to shells from the early Little Ice Age (ca. AD 1321-1391) and during the late 19th century (AD 1864-1886). Additionally, seasonal oxygen isotope data suggest that summers were cooler and winters were warmer in the Gulf of Maine during the 11th century compared to summers and winters in the 14th century and the late 19th century. The inferred decreased seasonality during Medieval times likely resulted from increased stratification of the coastal waters due to warmer seawater temperatures. As seawater cooled during the Little Ice Age, we suggest that increased vertical mixing of the coastal surface waters was a major driving factor for the observed increase in the amplitude of the seasonal seawater temperature cycle.

Records of environment contained within the accretionarily deposited tissues of fossil organisms afford a means of detailed reconstruction of past climates and hence of rigorous testing of numerical climate models. We identify the environmental factors controlling oxygen and carbon stable-isotopic composition, and microgrowth-increment size, in the shell of modern examples of the Queen Scallop, Aequipecten opercularis. This understanding is then applied in interpretation of data from mid-Pliocene A. opercularis from eastern England. On the basis of oxygen-isotope evidence we conclude that winter minimum seafloor temperature was similar to present values (typically 6–7 °C) in the adjacent southern North Sea and that summer maximum seafloor temperature was a few degrees lower than present values (typically 16–17 °C). This contrasts with evidence from other proxies that winter and summer temperatures were higher than present. The pattern of seasonal variation in microgrowth-increment size suggests the existence of intense thermal stratification in summer. We therefore conclude that summer surface temperatures were much higher (maxima well over 20 °C) than those recorded isotopically on the seafloor and that the annual range of surface temperature (probably over 14 °C) was greater than now at the times in the mid-Pliocene when the investigated A. opercularis were alive. Taken in conjunction with other proxy evidence of warmer winters as well as summers, the data point to substantial fluctuation (up to 10 °C) in winter minimum temperatures during the mid-Pliocene in the north-east Atlantic region. This fluctuation may be attributable to variation in the strength of the Gulf Stream/North Atlantic Drift. Since the Pliocene has been widely used as a test-bed for numerical models of a greenhouse Earth, the results have implications for prediction of future climate in the north-east Atlantic region under the influence of anthropogenic global warming.

The late Paleozoic ice age can be considered an important analogue to the modern ice age, but comparisons between the two time intervals have been hampered by the difficulty of resolving climatic changes that occur over short (e.g., seasonal) time scales in the Paleozoic record. As a first step toward overcoming these limitations, this study employed Mg/Ca trace element ratios sampled across the growth bands of six specimens of the brachiopod Composita to assess differences in tropical marine mean temperature and seasonality in Visean and Moscovian time. These time intervals bracket the onset of the late Paleozoic ice age, which occurred in mid-Serpukhovian time, and thus provide a snapshot of climate changes from a greenhouse to an icehouse world. Shells were screened for diagenetic alteration by cathode luminescence and by comparing the values of Mn, Sr, Na, and B to those reported for modern brachiopods. In addition, a 87Sr/86Sr value, measured for one specimen, agreed with a published strontium isotope curve for the late Paleozoic Era. Both the mean and range of Mg/Ca values were larger in Visean than Moscovian time, suggesting colder and less seasonal temperatures during the late Paleozoic ice age. The decline in seasonality was due to a greater proportional reduction of maximum values (which presumably represent summer temperatures) than minimum values. These relative differences between the pre-ice age and ice age tropical climate provide a first step toward understanding the broad patterns of seasonal-scale changes in temperature during a critical time in Earth's history.

Annual growth increment patterns of cardinal teeth (CT) of Panopea abrupta (Conrad) can reportedly provide information about past climate variations. However, little is known about the intra-annual timing and rate of shell growth necessary to interpret such records. In addition, it remains unclear whether actual temperatures can be reliably inferred from δ18O values of geoduck {goo'e-duk} shells. This study compared high-resolution environmental records (hourly to monthly resolved temperature, bi-weekly to monthly δ18Owater and salinity data) with temperatures reconstructed from oxygen isotope values of the outer shell layer (Tδ18OOSL) and cardinal tooth portions (Tδ18OCT) of different contemporaneous specimens alive at the same locality. Results indicate that shell growth mainly occurred between March/April and November/December with a maximum during May–August. This finding must be considered when comparing the “annual” growth increment width chronologies to environmental parameters. In addition, intra-annual δ18Oshell values require the calculation of weighted averages instead of arithmetic means. During ontogeny, the duration of the growing season remained nearly unchanged; an important finding for paleoclimate studies based on inter-annual growth patterns. Seasonal shell growth was strongly correlated with temperature (R = 0.93, R2 = 0.86, p

We measured annual shell growth rates of a 374-year-old (radiometrically confirmed) bivalve mollusk specimen of Arctica islandica (Linnaeus). This bivalve represents the oldest ever reported individual animal. In addition, we analyzed 1051 individual powder samples from ontogenetic years two to 40 (=80% of the entire shell height) for isotope analyses. Oxygen and carbon isotopes exhibit clear intra-annual cycles. The highest measured carbon isotope values (on average+2.73x) occurred during summer, i.e., during maximum primary productivity. The d 18 Oaragonite-derived temperature time-series cover the period of AD 1496–1533. Temperatures calculated from oxygen isotopes ranged from 4.5 to 9.3 8C and exhibit a mean value of 6.2 8C. The latter coincides well with the 1854–2003 mean value of 6.81 8C for sea-surface temperature between February and September (=growing season of A. islandica). Neither oxygen nor carbon isotopes exhibit age-related, unidirectional trends. However, d 13 Caragonite and d 18 Oaragonite values fluctuated at decadal periods of four, six and eight to nine years (NAO-type periods) as well as 12–14 years which may represent teleconnections to cycles in the tropical Atlantic. Annual shell growth is positively correlated to intra-annual d 18 Oaragonite minima, i.e., warm summer temperatures (R 2 =0.34), and to intra-annual d 13 Caragonite minima (higher food supply; R 2 =0.42). Using a linear multiregression model, 65% of the variation in annual shell growth can be explained by summer temperature and food supply. The formation of extremely narrow annual increments coincides with major volcanic eruptions (e.g., Tambora 1815). A period of extremely variable growth occurred during the culmination of the Little Ice Age in Iceland between ca. AD 1550 and 1620. Shell growth during AD 1765–1780, however, was characterized by very little year-to-year variability, probably as the result of extremely mild climate near the end of the Little Ice Age. This study demonstrates that shells of A. islandica provide

Accretionary hard parts of many organisms provide excellent archives of past climate and environmental conditions or life history traits. Variable growth rates function as environmental and physiological proxies, and growth increments as calendars. Recognition of growth structures is thus a prime necessity for sclerochronological studies. Here we present a new, handy, easy-to-use and time-efficient technique that resolves annual and sub-annual growth structures in skeletons of a wide range of different organisms. Mutvei's solution simultaneously etches biogenic carbonates and calcium phosphates, fixates the soluble and insoluble organic matrices and fibers, and stains mucopolysaccharides. It produces a filigreed three-dimensional relief of etch-resistant ridges (growth lines) and etched depressions (growth increments) and stains skeletal growth structures in shadings of blue. Growth lines stand out as crisp, darker-blue stained lines. Reflected optical light microscopy (axial and oblique illumination) and scanning electron microscopy can be used to analyze the microgrowth structures. We demonstrate the use of the technique on hard tissues of various marine and freshwater bivalves, a coral, a sclerosponge, a barnacle, gastropods, a cephalopod, a fish otolith and a whale's ear bone. This technique may be of interest for paleoclimatologists, geochemists and biologists. It can significantly expand the use of biogenic hard parts as environmental and physiological indicators because it reveals microgrowth structures of biogenic skeletons that potentially form on a periodic basis and thus function as calendars.

Although climate system modeling cannot be imagined without long sea surface temperature (SST) records, observational data is spatiotemporally incomplete and inhomogeneous prior to about 1950. Moreover, almost no high-resolution SST proxies exist from temperate and boreal marine settings. Here, we present a temporally equidistant, high-resolution SST proxy record of the southern North Sea during the period 1884–1983 calculated from oxygen isotope ratios (δ18Oaragonite) of Arctica islandica (L.), a bivalve mollusk shell. Arctica islandica produces daily growth increments, which enable precise intraannual dating. The growing season of specimens from about 25 m water depth (upper well-mixed layer of the ocean) started in February and ended in September. Observational (COADS, etc.) and δ18Oaragonite-derived SST data during February through September compare well to each other, especially after 1950. Apart from similar overall SST trends, we found North Atlantic Oscillation-type cycles of 7–9 years in our proxy SST record and in various different instrumentally determined SST chronologies. No vital effects exist, so that δ18Oaragonite ratios determined across the shell (i.e., throughout lifetime) of the studied specimen reflect ambient water temperatures that occurred during shell growth. Results of our study demonstrate that A. islandica provides long, independent and high-resolution SST proxy chronologies from higher latitudes. Such records can complement and further validate observational SST data and help improving climate system models.

In principle, bivalve mollusks living at the same time and in the same place will experience the same temperature and salinity regimes and will have identical annual oxygen isotope ( δ 18 O) profiles. Bivalve mollusks living at different times or in different places are more likely to have different annual δ 18 O profiles. Thus, differences in annual δ 18 O profiles can be used to detect temporal or spatial mixing. We devised eight metrics to quantitatively compare sclerochronologically calibrated annual δ 18 O profiles from different shells: difference in maximum value, difference in minimum value, difference in amplitude, the number of non-contemporaneous isotopic enrichment events (NNEE), the average fortnightly difference (AD), the standard deviation of the average fortnightly differences (SDD), the maximum fortnightly difference (MaxD) and the number of fortnights separating the minimum values. These metrics vary among northern Gulf of California shells from four temporal and spatial categories: (1) same time and same place; (2) same time and different place; (3) different time and same place; and (4) different time and different place. Different time/different place comparisons include comparisons of live-collected shells with shells alive during times of Colorado River flow and shells from a Pleistocene interglacial deposit. The same time/same place comparison has the most similar metric values, whereas comparisons among the different time/different place shells are usually the least similar. Between-shell oxygen isotope differences can reveal temporal or spatial mixing of shells that would be undetectable with radiocarbon or amino-acid racemization dating. Application of the technique to a Holocene deposit with shells in life position reveals that the bivalves were alive at different times, despite indistinguishable radiocarbon ages. Two adjacent but disarticulated Pleistocene shells appear to be both temporally and spatially mixed. The method can detect temporal or spatial mixing in any shell material unaffected by diagenesis, regardless of the age of the specimens.

We establish a model for the reconstruction of average daily sea surface temperatures from calcification rates of an intertidal bivalve mollusk. The rate of shell production in Chione cortezi (Carpenter, 1864, ex Sloat MS) is mainly controlled by water temperature, ontogenetic age and the effect of tidal cycles. Statistical methods developed by dendrochronologists can successfully extract the water temperature signal from daily growth increment chronologies. After removal of noise, the growth rates are expressed as scaled daily growth indices. Average daily water temperatures during the first half of the year are highly correlated with the scaled daily growth index values of recent and subrecent specimens, using the multi-valued function presented here. Increment width analysis can reconstruct daily average water temperatures with a mean error of less than 3%. This technique provides an independent method for reconstructing temperatures in fossil specimens of species with living representatives and can supplement high-resolution temperature reconstructions based on geochemical analysis.