Search

Oxygen isotope (δ18O) sclerochronology of benthic marine molluscs provides a means of reconstructing the seasonal range in seafloor temperature, subject to use of an appropriate equation relating shell δ18O to temperature and water δ18O, a reasonably accurate estimation of water δ18O, and due consideration of growth-rate effects. Taking these factors into account, δ18O data from late Pliocene bivalves of the southern North Sea basin (Belgium and the Netherlands) indicate a seasonal seafloor range a little smaller than now in the area. Microgrowth-increment data from Aequipecten opercularis, together with the species composition of the bivalve assemblage and aspects of preservation, suggest a setting below the summer thermocline for all but the latest material investigated. This implies a higher summer temperature at the surface than on the seafloor and consequently a greater seasonal range. A reasonable (3 ∘C) estimate of the difference between maximum seafloor and surface temperature under circumstances of summer stratification points to seasonal surface ranges in excess of the present value (12.4 ∘C nearby). Using a model-derived estimate of water δ18O (0.0 ‰), summer surface temperature was initially in the cool temperate range ( ∘C) and then (during the Mid-Piacenzian Warm Period; MPWP) increased into the warm temperate range (>20 ∘C) before reverting to cool temperate values (in conjunction with shallowing and a loss of summer stratification). This pattern is in agreement with biotic-assemblage evidence. Winter temperature was firmly in the cool temperate range ( ∘C) throughout, contrary to previous interpretations. Averaging of summer and winter surface temperatures for the MPWP provides a figure for annual sea surface temperature that is 2–3 ∘C higher than the present value (10.9 ∘C nearby) and in close agreement with a figure obtained by averaging alkenone and TEX86 temperatures for the MPWP from the Netherlands. These proxies, however, respectively, underestimate summer temperature and overestimate winter temperature, giving an incomplete picture of seasonality. A higher annual temperature than now is consistent with the notion of global warmth in the MPWP, but a low winter temperature in the southern North Sea basin suggests regional reduction in oceanic heat supply, contrasting with other interpretations of North Atlantic oceanography during the interval. Carbonate clumped isotope (Δ47) and biomineral unit thermometry offer means of checking the δ18O-based temperatures.

As part of the HIPPO (HIgh-resolution Primary Production multi-prOxy archives) project, an environmental monitoring was carried out between March and October 2021 in the Bay of Brest. The aim of this survey was to better understand the processes which drive the incorporation of chemical elements into scallop shells and their links with phytoplankton dynamics. For this purpose, biological samples (scallops and phytoplankton) as well as water samples were collected in order to analyse various environmental parameters (element chemical properties, nutrients, chlorophyll, etc.). Here, some of the monitoring data are presented and discussed. The whole dataset is much larger and can potentially be very useful for other scientists performing sclerochronological investigations, studying biogeochemical cycles or conducting various ecological research projects.

The chemical composition of mollusk shells is a useful tool in (paleo)climatology since it captures inter- and intra-annual variability in environmental conditions. Trace element and stable isotope analyses with improved sampling resolution now enable the use of mollusk shells for paleoenvironmental reconstructions at a daily to sub-daily resolution. Here, we discuss hourly resolved Mg/Ca, Mn/Ca, Sr/Ca and Ba/Ca profiles measured by laser ablation ICP-MS through shells of photosymbiotic giant clams (Tridacna maxima, Tridacna squamosa and Tridacna squamosina) and the non-photosymbiotic scallop Pecten maximus. Precise sclerochronological age models and spectral analysis allowed us to extract daily and tidal rhythms in the trace element composition of these shells. We find significant expression of these periodicities but conclude that this cyclicity explains less than 10 % of the sub-annual variance in trace element profiles. Tidal and diurnal rhythms explain variability of at most 0.2 mmol/mol (~10 % of mean value) in Mg/Ca and Sr/Ca, while Mn/Ca and Ba/Ca cyclicity has a median amplitude of less than 2 µmol/mol (~40 % and 80 % of the mean of Mn/Ca and Ba/Ca, respectively). Daily periodicity in Sr/Ca and Ba/Ca is stronger in Tridacna than in Pecten, with Pecten showing stronger tidal periodicity. One T. squamosa specimen which grew under a sunshade exhibits some of the strongest diurnal cyclicity. Daily cycles in trace element composition of giant clams are therefore unlikely to be driven by variations in direct insolation itself but reflect an inherent biological rhythmic process affecting element incorporation. Finally, the large amount of trace element variability unexplained by periodic variability highlights the dominance of aperiodic processes in mollusk physiology and/or environmental conditions on shell composition at the sub-daily scale. Future studies should aim to investigate whether part of this aperiodic variability in shell chemistry reliably records weather patterns or circulation changes in the paleoenvironment.

Molar barium-to‑calcium ratios in bivalve shells (Ba/Cashell) have been proposed in a variety of studies to serve as a potential proxy for the reconstruction of phytoplankton dynamics. However, the link between phytoplankton and Ba/Cashell profiles remains unclear and needs to be deciphered more accurately. In this study, we analyzed the relationship between Ba/Cashell peaks and specific phytoplankton species, and assessed the applicability of Ba/Cashell ratios as a species-specific phytoplankton proxy. The timing of peaks in highly resolved Ba/Cashell time-series in Pecten maximus shells (Bay of Brest, France) from two years (2011, 2012) were compared to the chlorophyll a concentration and the occurrence of individual diatom and dinoflagellate species. In addition, Monte Carlo simulations were used to approximate a species-specific contribution to the measured Ba/Cashell peaks. The results clearly demonstrated that the Ba/Cashell profiles cannot be explained either by the chlorophyll a concentration nor by the total diatom or dinoflagellate abundance. Instead, time-series of specific phytoplankton, especially diatoms, revealed a high degree of synchronicity with Ba/Cashell peaks when temporally lagged by 8 to 13 days (depending on species). The Monte Carlo simulations suggested that the Ba/Cashell peak heights cannot be fully explained by the observed phytoplankton cell concentration, but rather by individually weighted phytoplankton time-series, most likely caused by inter-species differences such as cell size and chemical ability to adsorb Ba. Moreover, the approximated species-specific weighting factors agreed well between the studied years. According to our findings, Ba/Cashell peaks are likely associated with blooms of specific phytoplankton taxa, with a time lag of ca. one to two weeks, and the amount of cell-associated Ba varies between phytoplankton species. These conclusions provide further insights into the formation of Ba enrichments in bivalve shells and improves the applicability of Ba/Cashell profiles as a species-specific proxy of past phytoplankton dynamics.

The stable isotope composition of lacustrine sediments is routinely used to infer Late Holocene changes in precipitation over Scandinavia and, ultimately, atmospheric circulation dynamics in the North Atlantic realm. However, such archives only provide a low temporal resolution (ca. 15 years), precluding the ability to identify changes on inter-annual and quasi-decadal timescales. Here, we present a new, high-resolution reconstruction using shells of freshwater pearl mussels, Margaritifera margaritifera, from three streams in northern Sweden. We present seasonally to annually resolved, calendar-aligned stable oxygen and carbon isotope data from 10 specimens, covering the time interval from 1819 to 1998. The bivalves studied formed their shells near equilibrium with the oxygen isotope signature of ambient water and, thus, reflect hydrological processes in the catchment as well as changes, albeit damped, in the isotope signature of local atmospheric precipitation. The shell oxygen isotopes were significantly correlated with the North Atlantic Oscillation index (up to 56 % explained variability), suggesting that the moisture that winter precipitation formed from originated predominantly in the North Atlantic during NAO+ years but in the Arctic during NAO− years. The isotope signature of winter precipitation was attenuated in the stream water, and this damping effect was eventually recorded by the shells. Shell stable carbon isotope values did not show consistent ontogenetic trends, but rather oscillated around an average that ranged from ca. −12.00 to −13.00 ‰ among the streams studied. Results of this study contribute to an improved understanding of climate dynamics in Scandinavia and the North Atlantic sector and can help to constrain eco-hydrological changes in riverine ecosystems. Moreover, long isotope records of precipitation and streamflow are pivotal to improve our understanding and modeling of hydrological, ecological, biogeochemical and atmospheric processes. Our new approach offers a much higher temporal resolution and superior dating control than data from existing archives.

The Mini Carbon Dating System (MICADAS) represents a flexible AMS system for measuring radiocarbon samples either in the form of graphite or CO2 gas. We used the possibility to attach a carbonate handling system (CHS) to the gas ion source (GIS) to measure smaller amounts of carbonates ( 3) are used to clean the system. We tested the CHS-GIS combination on heated and unheated archaeological shells of Anadara uropigimelana from Kalba, Sharjah Emirate, United Arab Emirates (UAE). Even though the amount of carbon in the samples was small (4–22 µg C) the performance of the CO2 dating system permits the comparison of trends in the 14C data to stable isotope measurements (δ18O and δ13C). With 10–20 µg C, however, our sample sizes were too small, suffering from cross-contamination and elevated blanks, and our blank samples prior to the small samples were not enough. Hence, an interpretation in combination with the stable isotope data was not possible beyond comparison of trends.

Organismal metabolic rates reflect the interaction of environmental and physiological factors. Thus, calcifying organisms that record growth history can provide insight into both the ancient environments in which they lived and their own physiology and life history. However, interpreting them requires understanding which environmental factors have the greatest influence on growth rate and the extent to which evolutionary history constrains growth rates across lineages. We integrated satellite measurements of sea-surface temperature and chlorophyll-a concentration with a database of growth coefficients, body sizes, and life spans for 692 populations of living marine bivalves in 195 species, set within the context of a new maximum-likelihood phylogeny of bivalves. We find that environmental predictors overall explain only a small proportion of variation in growth coefficient across all species; temperature is a better predictor of growth coefficient than food supply, and growth coefficient is somewhat more variable at higher summer temperatures. Growth coefficients exhibit moderate phylogenetic signal, and taxonomic membership is a stronger predictor of growth coefficient than any environmental predictor, but phylogenetic inertia cannot fully explain the disjunction between our findings and the extensive body of work demonstrating strong environmental control on growth rates within taxa. Accounting for evolutionary history is critical when considering shells as historical archives. The weak relationship between variation in food supply and variation in growth coefficient in our data set is inconsistent with the hypothesis that the increase in mean body size through the Phanerozoic was driven by increasing productivity enabling faster growth rates.

A reconstruction of sea surface temperature (SST) spanning 45 years (1966–2011) was developed from δ18O obtained from the aragonitic shells of Glycymeris glycymeris, collected from the Bay of Brest, France. Bivalve sampling was undertaken monthly between 2014 and 2015 using a dredge. In total, 401 live specimens and 243 articulated paired valves from dead specimens were collected, of which 24 individuals were used to reconstruct SST. Temperatures determined using the palaeotemperature equation of Royer et al. compared well with observed SST during the growing season between 1998 and 2010 (Pearson’s correlation: p = 0.002, r = 0.760). Furthermore, a significant negative correlation was found between the reconstructed SST and the North Atlantic Subpolar Gyre (SPG) index ( p = 0.001, r = −0.50), and a significant positive correlation was found with the East Atlantic Pattern (EAP) index when the reconstructed SST was lagged by 1 year ( p = 0.002, r = 0.46). This led to the conclusion that EAP and SPG are major influences on SSTs in the Bay of Brest. As the SPG controls air temperature in Northern Europe and the EAP controls water temperature in Southern Europe, this suggests that the Bay of Brest is an interaction area between these two climate systems. As such, this locality is interesting as the δ18O of the shells can be used as a proxy for both the SPG and EAP, and temperature reconstructions can provide a unique insight into how these climate systems interacted prior to the instrumental era.

Mollusc shell stable isotopes are commonly used to reconstruct past environmental conditions. However, despite being abundant components of natural and anthropogenic fossil accumulations, the geochemical composition of mussel shells ( Mytilus spp.) has rarely received attention in palaeoenvironmental studies. This study tests the suitability of oxygen isotopes (δ18Os) of Mytilus galloprovincialis as palaeothermometer. For 1 year, mussels and water samples were collected twice a month from Berria Beach, in Northern Spain. The geochemical data of the shells indicate that water temperatures can be reconstructed with an average offset of 1.2 ± 0.7°C with respect to the measured values. Furthermore, no prolonged shell growth cessations are observed. These results validate M. galloprovincialis as reliable recorders of seasonal water temperature fluctuations, supporting their use in palaeoenvironmental studies. In addition, further shell and water collections were carried out in the upper and lower areas of a nearby estuary. The geochemical analyses of these shells were aimed to test whether oxygen and carbon stable isotopes (δ13Cs) may be used as novel proxies to identify the shell provenance at local scale. The results show that the δ18Osversus δ13Cscorrelation direction varies along the coast–upper estuary geographical gradient, suggesting it to be a potential new proxy to distinguish between marine and estuarine mussel specimens.

Since magnesium concentration (Mg/Ca) in biogenic calcite is considered to reflect water temperature during precipitation, the magnesium-to‑calcium ratio has been examined as a proxy for water temperature in paleoclimate research, although factors other than temperature may also influence Mg/Ca in biogenic calcite, thereby introducing a potential bias in the relationship between Mg/Ca and temperature observed in inorganic systems. To better understand factors controlling Mg incorporation into the calcitic shells of bivalves, the distribution of Mg in the Mediterranean mussel Mytilus galloprovincialis was studied, being compared with ambient sea surface temperature (SST), shell growth rate and the distribution of organic matter. Although a positive relationship between Mg/Ca and SST was observed, Mg/Ca had been influenced by additional factors, including the enhancement of Mg incorporation by organic matter, evidenced by the growth line being more Mg-enriched than the growth increments. Furthermore, Mg/Ca was relatively enriched in the undulating (higher curvature) shell portion, being linked to neither SST, growth rate or organic matter. Zoning of Mg2+/Ca2+ within extrapallial fluid at the time of undulating shell portion formation was hypothesized, and heterogeneous Mg distribution in contemporaneously formed shell portions concluded as limiting the usability of Mytilus shell Mg/Ca as a proxy for water temperature.

Understanding the recruitment variability of the Atlantic herring North Sea stock remains a key objective of stock assessment and management. Although many efforts have been undertaken linking climatic and stock dynamic factors to herring recruitment, no major attempt has been made to estimate recruitment levels before the 20th century. Here, we present a novel annually resolved, absolutely dated herring recruitment reconstruction, derived from stable carbon isotope geochemistry (δ¹³C), from ocean quahog shells from the Fladen Ground (northern North Sea). Our age model is based on a growth increment chronology obtained from fourteen shells. Ten of these were micromilled at annual resolution for δ¹³C analysis. Our results indicate that the anthropogenically driven relative depletion of ¹³C, the oceanic Suess effect (oSE), became evident in the northern North Sea in the 1850s. We calculated a regression line between the oSE‐detrended δ¹³C results (δ¹³CṠ) and diatom abundance in the North Sea, the regression being mediated by the effect of phytoplankton on the δ¹³C of the ambient dissolved inorganic carbon. We used this regression to build an equation mediated by a nutritional link to reconstruct herring recruitment using δ¹³CṠ. The reconstruction suggests that there were five extended episodes of low‐recruitment levels before the 20th century. These results are supported by measured recruitment estimates and historical fish catch and export documentation. This work demonstrates that molluscan sclerochronological records can contribute to the investigation of ecological baselines and ecosystem functioning impacted by anthropogenic activity with implications for conservation and stock management.

Here we present novel cave-analogue experiments directly investigating stable carbon and oxygen isotope fractionation between the major involved species of the carbonate system (HCO3−, CO2, CaCO3 and H2O). In these experiments, which were performed under controlled conditions inside a climate box, a thin film of solution flew down an inclined marble or glass plate. After different distances of flow and, thus, residence times on the plate, pH, electrical conductivity, supersaturation with respect to calcite, precipitation rate as well as the δ18O and δ13C values of the dissolved inorganic carbon (DIC) and the precipitated CaCO3 were obtained. Progressive precipitation of CaCO3 along the plate is accompanied by degassing of CO2 and stable isotope fractionation, and the system is driven out of isotope equilibrium. We observe a strong enrichment of the δ13C values with increasing residence time and a smaller enrichment in δ18O. The temporal evolution of the δ18O and δ13C values of both the DIC and the precipitated CaCO3 can be explained by a Rayleigh fractionation model, but the observed enrichment in δ13C values is much larger than expected based on isotope equilibrium fractionation factors. Our setup enables to determine the fractionation between CaCO3 and HCO3−, i.e., eCaCO3/HCO3−. Carbon isotope fractionation, 13eCaCO3/HCO3−, is strongly negative for all experiments and much lower than equilibrium isotope fractionation (0–1‰). In addition, 13eCaCO3/HCO3− decreases with increasing residence time on the plate, and thus decreasing supersaturation with respect to calcite. Thus, isotope fractionation depends on precipitation rate and consequently occurs under kinetic conditions. This is in contrast to previous studies, which found no rate-dependence and no or even a positive carbon isotope fractionation between CaCO3 and HCO3−. Oxygen isotope fractionation, 18eCaCO3/HCO3−, is also negative and dependent on precipitation rate. Since no literature values for 18eCaCO3/HCO3− are available, we calculated 18eCaCO3/HCO3− using equilibrium oxygen isotope fractionation factors between water and calcite and water and HCO3−, respectively. At the beginning of the plate, the fractionation is in agreement with the fractionation calculated using fractionation factors determined in cave systems. The observed fractionation between CaCO3 and water, 1000ln18α, is also in good agreement with the values determined in cave systems and shows a very similar temperature dependence 1000 ln 18 α = 16.516 ± 1.267 ∗ 10 3 T − 26.141 ± 4.356 . However, with progressive precipitation of CaCO3 along the plate, the system is forced out of isotope equilibrium with the water, and 1000ln18α increases. The large, negative, rate-dependent isotope fractionations observed in this study suggest that precipitation of speleothem calcite is strongly kinetically controlled and may, thus, have a large effect on speleothem δ18O and δ13C values. Since these values may erroneously be interpreted as reflecting changes in past temperature, precipitation and/or vegetation density, these results have important implications for paleoclimate reconstructions from speleothems.

Oxygen depletion threatens an increasing number of shallow water environments, specifically habitats below the seasonal halocline in coastal settings of the Baltic Sea. To understand the natural variations of dissolved oxygen levels on seasonal and inter-annual time-scales prior to the instrumental era, high-resolution archives are urgently required. The present study evaluates the potential use of Mn/Ca values in shells of the bivalve, Arctica islandica to infer concentrations of past dissolved oxygen concentrations. This study is based on laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) data of six contemporaneous specimens and demonstrates that background variations of shell Mn/Ca are inversely linked to dissolved oxygen concentrations in the water column (r = −0.68; R2 = 0.46, p < 0.0001), which in turn are coupled to the amount of dissolved Mn. The regular seasonal changes were superimposed by sharp Mn/Ca peaks, most likely resulting from the ingestion of a large amount of Mn-rich organic particles. The availability of such particles can increase due to the resuspension of food particles by strong bottom currents or alternatively, result from increased particle flux from surface waters after major river discharges and subsequent phytoplankton blooms. Besides sharp Mn/Ca peaks, often accompanied by sharp Ba/Ca peaks and increased shell growth rate. In addition, after exceptional major barotropic inflows from the North Sea, the biogeochemical steady-state conditions remained disturbed for up to ca. two years, because the redox-sensitive elements were removed from the water column by oxygenated waters, and it took time for them to build up again in the water column. Therefore, subsequent to such Major Baltic Inflows (MBIs), dissolved Mn levels and shell Mn/Ca values were strongly reduced despite summertime low-oxygen conditions. As demonstrated here, Mn/Ca data of A. islandica shells can potentially serve as a proxy for dissolved oxygen levels in the water column. To further develop this proxy, a set of additional environmental and physiological proxies such as shell Ba/Ca values and growth rate should be critically assessed and used in combination with shell Mn/Ca.

The Smooth clam Callista chione is a commercially important venerid bivalve. It is widely distributed in the eastern Atlantic Ocean and the Mediterranean Sea and inhabits sandy sediments in coastal waters at depths down to 180 m. With specimens that can reach 10 cm of shell length and with a lifespan of more than four decades, C. chione represents an interesting archive for sclerochronological research. The aim of this study was to analyse possible variations in δ18Oshell and δ13Cshell values between C. chione specimens collected in different parts of the Mediterranean Sea.Callista chione shells were collected alive from three localities: (1) Caleta de Vélez in the north region of the Alborán Sea, Spain; (2) Gulf of Venice, Italy, North Adriatic, and (3) west coast of the Istrian peninsula, Croatia, also in the North Adriatic. At the first two localities, specimens were obtained from catch of the commercial fishing vessels, while in Istria they were collected by SCUBA diving. Prior to analysis, the external shell surface was physically cleaned by grinding. Shell powder for δ18Oshell and δ13Cshell analysis was then collected by milling narrow sample swaths in the outer shell surface and processed at Mainz University using a GasBench II - IRMS.Modelled daily temperature and salinity values were obtained for each locality and used for calculating the predicted δ18Oshell values. For Caleta de Vélez, daily temperature and salinity values were obtained by MEDSEA model; for the Venetian region by the AdriSC climate model, and for Istria by the 3D numerical model ROMS. Temporal alignment of measured δ18Oshell values was conducted manually in Excel by best-fitting measured isotope data to predicted δ18Oshell curves.Seasonal δ18Oshell cycles were observed in all studied specimens. Temporal alignment of measured and modelled δ18Oshell values clearly showed that C. chione grew fast during the warm part of the year, while slower growth occurred during the winter months. Samples collected in Caleta de Vélez had the narrowest range of δ18Oshell values (-0.43 to +1.73 ‰), while δ18Oshell values in C. chione from Istria showed the largest amplitudes (-1.61 to +2.67 ‰). Growth patterns varied between sampling localities.The δ13Cshell values varied strongly between localities and specimens. Highest δ13Cshell values were obtained for C. chione shells from Caleta de Vélez (0.51 ± 0.03 ‰, range -0.19 to +1.06 ‰). The broadest range of δ13Cshell values (-3.37 to -0.08 ‰) were measured in shells from the Venetian region. These samples also had the lowest mean (-1.42 ± 0.14 ‰). Shells from Istria had δ13Cshell values ranging from -1.57 to +0.38 ‰ (mean: -0.42 ± 0.28 ‰). Observed differences between localities are statistically significant (Kruskal Wallis H = 150.4, p < 0.001). Isotope data obtained for this study were compared with data from a previous study on the same species in the Eastern Adriatic.Research was supported by the Croatian Science Foundation, research project BivACME.

Bivalve shells have a long-standing reputation as archives for high-resolution (seasonal scale) (paleo)climate variability due to their incremental growth, yielding accurate shell chronologies, and their abundance, diversity, and high preservation potential in the fossil record (Schöne and Surge, 2012). Capitalizing on innovations in geochemical techniques, high-resolution sclerochronology can now resolve changes in bivalve shell chemistry beyond the daily resolution (e.g. Sano et al., 2012; Warter et al., 2018). When applied on fossil shells, these ultra-high-resolution records have the potential to bridge the gap between climate and weather reconstructions and yield unprecedented information about bivalve paleobiology, extreme weather events in past climates and even astronomical cycles (Warter and Müller, 2017; de Winter et al., 2020; Yan et al., 2020).However, studies of sub-daily scale shell chemistry are almost exclusively limited to giant clams (Tridacna spp.), due to their high growth rates. It is hitherto unknown if and how such diurnal cycles in chemistry differ in other genera across the bivalve clade and/or whether they are exclusive to photosymbiotic clams. In addition, it is not clear whether the daily cycles are formed in response to environmental conditions (e.g. light or temperature sensitivity) or reflect circadian rhythms.To answer these questions, we combine ultra-high-resolution (hourly scale) Laser Ablation ICP-MS trace element profiles through shells of various tridacnid species from the tropical Gulf of Aqaba with profiles through the giant scallop (Pecten maximus) from the temperate Atlantic coast of northwestern France. We observe trace element cycles on in the daily frequency domain in both tridacnids and pectinids. This shows that these diurnal cycles are formed regardless of shell mineralogy (aragonite vs. calcite), living environment (tropical inter-tidal vs. temperate sub-tidal) and occur in highly unrelated bivalve taxa. Our data helps the interpretation of similar records from fossil shells in terms of past (extreme) weather events, climate, and shell growth. Referencesde Winter, N. J. et al. Paleoceanography and Paleoclimatology 35, e2019PA003723 (2020).Sano, Y. et al. Nature Communications 3, 761 (2012).Schöne, B. R. & Surge, D. M. Treatise Online 24, Volume 1, Chapter 14 (2012).Warter, V., Erez, J. & Müller, W. Palaeogeography, Palaeoclimatology, Palaeoecology 496, 32–47 (2018).Warter, V. & Müller, W. Palaeogeography, Palaeoclimatology, Palaeoecology 465, 362–375 (2017).Yan, H. et al. PNAS 117, 7038–7043 (2020).

Various elements of the biota of the early Pliocene Coralline Crag Formation (southern North Sea Basin, eastern England) have been taken to indicate a warm temperate marine climate, with summer surface temperatures above 20 °C and winter temperatures above 10 °C [1]. However, summer and winter temperature estimates from oxygen-isotope (δ18O) sclerochronology of benthic invertebrates are typically in the respective cool temperate range when calculated using a plausible modelled value for water δ18O of +0.1‰. For instance, examples of the bivalve mollusc Aequipecten opercularis from the Ramsholt Member indicate summer maximum temperatures of 11.0–15.7 °C and winter minimum temperatures of 4.4–7.1 °C [2]. Amongst other evidence, the pattern of microgrowth-increment variation in Ramsholt-Member A. opercularis points to a depth below the summer thermocline, hence the temperatures recorded for that season provide an underestimate of surface temperature; this may well have been in the warm temperate summer range [2], as suggested by the pelagic dinoflagellate biota [3]. However, the cool temperate benthic winter temperatures indicated by isotopic data are likely also to have obtained at the surface, pointing to a greater seasonal range in surface temperature (perhaps > 15 °C) than in the modern North Sea (< 13 °C) [2]. This conclusion is not changed by adoption of a different (invariant) value for water δ18O and also follows from data for a specific late Pliocene interval (Mid-Piacenzian Warm Period) elsewhere in the southern North Sea Basin (Belgium, Netherlands [4]). Here we present isotopic evidence of a seasonal range in surface temperature higher than now at other times in the late Pliocene. Examples of A. opercularis from several horizons in the Lillo Formation (Belgium) and the Oosterhout Formation (Netherlands) indicate seasonal ranges in benthic temperature of 10–14 °C. Seasonal variation in water δ18O can only plausibly account for about 1 °C of these ranges. Taking into consideration microgrowth-increment evidence of a setting below the summer thermocline, the seafloor ranges imply that the surface seasonal range was sometimes 17 °C or more. Other bivalves (Atrina fragilis, Arctica islandica, Pygocardia rustica, Glycymeris radiolyrata) do not indicate such a high seasonal range in benthic (and hence surface) temperature but this can be attributed to inadequate sampling—time-averaging or a failure to recover evidence of seasonal extremes because of growth breaks. The high surface temperature range could reflect a reduction in vigour of the North Atlantic Current and hence diminished oceanic supply of heat in winter.References:[1] Vignols et al. (2019), Chem. Geol. 526, 62–83. https://doi.org/10.1016/j.chemgeo.2018.05.034.[2] Johnson et al. (2020), Palaeogeogr. Palaeoclimatol. Palaeoecol. 561. https://doi.org/10.1016/j.palaeo.2020.110046.[3] Head (1997), J. Paleontol. 71, 165–193. https://doi.org/10.1017/S0022336000039123.[4] Valentine et al. (2011), Palaeogeogr. Palaeoclimatol. Palaeoecol. 309, 9–16. https://doi.org/10.1016/j.palaeo.2011.05.015.

The shell δ18O of young modern Aequipecten opercularis from the southern North Sea provides an essentially faithful record of seasonal variation in seafloor temperature. In this well-mixed setting, A. opercularis shell δ18O also serves as a proxy for seasonal variation in surface temperature. Individuals from less agitated (e.g. deeper) settings in a warm climate would not be expected to record the full seasonal range in surface temperature because of thermal stratification in summer. Such circumstances have been invoked to explain cool isotopic summer temperatures from early Pliocene A. opercularis of eastern England. Support for a sub-thermocline setting derives from high-amplitude variation in microgrowth-increment size, which resembles the pattern in sub-thermocline A. opercularis from the southern Mediterranean Sea. Here, we present isotope and increment profiles from further sub-thermocline individuals, live-collected from a location in the Adriatic Sea for which we provide modelled values of expected shell δ18O. We also present data from supra-thermocline shells from the English Channel and French Mediterranean coast. The great majority of sub-thermocline A. opercularis show high-amplitude variation in increment size, and winter and summer δ18O values are generally quite close to expectation. However, the relatively warm summer conditions of 2015 are not recorded, in most cases due to a break in growth, perhaps caused by hypoxia. The supra-thermocline shells show subdued increment variation and yield isotopic winter and summer temperatures quite close to the local directly measured values. A. opercularis shells therefore provide a fairly good isotopic record of ambient temperature (if not always of relatively warm summer conditions below the thermocline) and their hydrographic setting can be determined from increment data. Early Pliocene examples from eastern England can be interpreted as having lived in a setting below the thermocline, with a higher seasonal range in surface temperature than now in the adjacent southern North Sea.

Geochimica et cosmochimica acta 308, 326-352 (2021). doi:10.1016/j.gca.2021.06.012, Published by Elsevier, New York, NY [u.a.]

Preface to Virtual Special Issue published in Palaeogeography, Palaeoclimatology, Palaeoecology

The shells of long-lived bivalves record environmental variability in their geochemical signatures and are thus used extensively in marine high-resolution paleoclimate studies. To possibly overcome the limitations of the commonly employed temperature proxy, the δ18Oshell value, which requires knowledge of the seawater δ18O signature and is prone to diagenetic overprint, the shell microstructures and the morphological properties of individual biomineral units (BMUs) recently attracted research interest as an alternative paleoclimate proxy. In shells of A. islandica, one of the most extensively used and best studied sclerochronological archives, the size of the BMUs increases in warmer temperatures under laboratory circumstances. This study assesses whether this relationship persists under natural growth conditions or whether additional environmental and physiological factors control the BMU size and bias temperature reconstructions. For this purpose, shells from the surface waters of NE Iceland and the Baltic Sea, as well as from deeper waters of the North Sea (100 and 243 m) were analyzed by means of SEM. The BMU sizes were measured by means of image processing software. Results demonstrate a strong effect of temperature on the BMU size at NE Iceland and in the North Sea at 100 m depth. At 243 m depth, however, temperature variability was likely too low (1.2°C) to evoke a microstructural change. At the Baltic Sea, the BMUs remained small, possibly due to physiological stress induced by low salinity and/or hypoxia. Thus, the size of BMUs of A. islandica shells only serves as a relative temperature indicator in fully marine habitats, as long as seasonal temperature amplitudes exceed ca. 1°C. Furthermore, BMU size varied through lifetime with the largest units occurring during age seven to nine. This pattern is possibly linked to the shell growth rate or to the amount of metabolic energy invested in shell growth.

Bivalve shells serve as powerful high-resolution paleoclimate archives. However, the number of reliable temperature proxies is limited. It has remained particularly difficult to extract temperature signals from shell Sr/Ca, although Sr is routinely employed in other biogenic aragonites. In bivalves, Sr/Ca is linked to the prevailing microstructure and is sometimes affected by kinetics. Here, the hypothesis is tested that temperature can be reconstructed from shell Sr/Ca once microstructure and/or growth-rate-related bias has been mathematically eliminated. Therefore, the relationship between Sr/Ca and increment width, as well as biomineral unit size, has been studied in three different shell portions of field-grown Arctica islandica specimens. Subsequently, microstructure and/or growth-rate-related variation was removed from Sr/Ca data and residuals compared to temperature. As demonstrated, the hypothesis could not be verified. Even after detrending, Sr/Ca remained positively correlated to water temperature, which contradicts thermodynamic expectations and findings from inorganic aragonite. Any temperature signal potentially recorded by shell Sr/Ca is overprinted by other environmental forcings. Unless these variables are identified, it will remain impossible to infer temperature from Sr/Ca. Given the coupling with the biomineral unit size, a detailed characterization of the microstructure should remain an integral part of subsequent attempts to reconstruct temperature from Sr/Ca.

The Kingdom of Portugal was established with the help of military-monastic orders, which provided important defence against Muslim armies during the 12th–13th century Christian conquest. While historical sources document the main events of this period, this research seeks to elucidate individual lifestyles and movement, aspects typically absent from written records. A multi-isotopic approach was used on skeletal material from eight Christian and two Muslim burials from Evora, Portugal (11th–13th centuries). Anthropological and archaeological evidence suggests the Christian adults belonged to the Evora Militia, which we seek to confirm through the reconstructed diet and mobility of these individuals. Stable carbon, nitrogen and sulphur isotopes were measured in bone collagen, and radiogenic strontium, carbonate stable oxygen and apatite stable carbon isotopes were measured in tooth enamel. Results of the stable oxygen and radiogenic strontium isotopes indicated diverse origins of the Christian population, while at least one individual was local. The Muslim adult was local, as anticipated. The δ13Cen (enamel) values provide evidence of childhood consumption of different cereals (C3 and C4), possibly linked to social status. The δ13Ccol (bone collagen) human values indicated mostly C3 diets with varying inputs of C4, while δ15N reflected high protein intake overall. The mean diet-consumer spacing of this population was compared to other isotopic studies from Medieval Iberia and other European monastic/convent populations. A visible trend emerged in populations that likely followed religious fasting rules, including the Evora Christians. The results of this study indicate that the Order of Evora was composed of members from diverse geographic and possibly social origins, an aspect previously unclear in written sources.

Bivalves offer outstanding potential as environmental archives. However, vital effects exert a strong control on the incorporation of many trace and minor elements into the shell so that their use as environmental proxies is currently limited. Furthermore, Sr and Mg show a strong relationship to the micrometer-sized shell architecture (shell microstructure), i.e., near growth lines, which are typically dominated by irregular simple/spherulitic prismatic microstructures, the concentrations of these elements are significantly higher than in portions between growth lines (= growth increments, which are microstructurally more complex). In contrast, Ba is uncoupled from the prevailing shell microstructure. To shed more light on these issues, we conducted a combined element chemical (in-situ analysis by means of LA-ICP-MS) and microstructural analyses (using SEM) of shells of Arctica islandica collected alive in NE Iceland.According to our findings, (1) contemporaneous shell portions in the hinge and ventral margin (both belonging to the outer shell layer) within individual specimens showed nearly identical Sr/Ca and Mg/Ca values, but Ba/Ca was 1.5 – 2.5 times higher in the ventral margin than in the hinge. (2) In agreement with previous studies, Sr and Mg were strongly elevated near annual growth lines. (3) Along an isochronous transect from the inner portion of the outer shell layer near the myostracum toward the outer shell surface (in the ventral margin), Si/Ca values increased, on average, by 75% ± 11%, whereas Na/Ca values decreased by 7% ± 1%. Along this transect, the shell microstructure gradually changed from crossed-acicular to homogeneous suggesting that Si and Na are linked to the prevailing nanometer-sized shell architecture or underlying physicochemical processes controlling their formation. (4) In the hinge, Ba/Ca, Sr/Ca, Mn/Ca and Mg/Ca attained highest values along the axis of maximum growth, but gradually decreased in slower growing (contemporaneous) shell portions away from that axis. (5) In contemporaneous shell portions (in either the hinge or the ventral margin), the concentration of some elements varied significantly among specimens, whereas others showed little variability. For example, in similar and contemporaneous shell portions of different specimens, Na/Ca values exhibited only little variation (17.4 – 23.7 mmol/mol), whereas Sr/Ca and B/Ca differed more severely (0.3 – 1.6 mmol/mol and 0.04 – 0.07 mmol/mol, respectively; both within growth increments). Despite these inter-specimen chemical differences, the shell microstructure remained largely invariant.Our findings firstly suggest that the extrapallial fluid, if it exists at all, is chemically inhomogeneous. This could result from differences in the efficiency of transmembrane ion transport or to differences in shell formation rate along the growing margin (e.g., faster growth in the outer portion of the outer shell layer than in portions closer to the myostracum). Secondly, chemical differences among specimens may be attributed to physiological differences. Thirdly, some elements such as Ba are uncoupled to microstructural properties, but co-vary strongly among specimens suggesting an environmental control on the uptake and incorporation of this element into the shell.

Bivalve shells serve as excellent high-resolution archives of marine paleoclimate. Recently, ultrastructural features of the shells were investigated as potential temperature proxies that can overcome the limitations of the stable oxygen isotope method (i.e., missing data on past seawater oxygen isotope signature and diagenetic overprint). According to previous studies, the size of individual biomineral units of prismatic, nacreous and crossed-lamellar ultrastructures in cross-sections along the axis of maximum growth was solely related to water temperature. Despite being present in 90% of all mollusks, the crossed-lamellar ultrastructure was only studied for environmental relationships in one species (Glycymeris bimaculata) until now. To determine whether this new proxy can be applied to other bivalves with crossed-lamellar ultrastructure, further studies are needed.We analyzed the shells of other Glycymerididae collected at near-shore and shelf environments (G. nummaria and G. pilosa: Adriatic Sea, Croatia; G. glycymeris: Iroise Sea, France; Glycymeris sp: Southern Pacific, New Zealand) by means of SEM, using a previously developed automatic image analysis procedure. Morphological changes of the biomineral units of the shells were assessed for relationships with temperature, salinity and food availability. Additionally, the crossed-lamellar architectures of phylogenetically more distantly related taxa (Venus verrucosa and Callista chione: Adriatic Sea, Croatia) were assessed.Our results show that all studied Glycymerididae species, irrespective of environmental setting and locality, formed larger biomineral units in warmer waters. However, biomineral properties of ontogenetically old shell portions are more difficult to interpret, because declining growth rates condense the shell record and aggravate ultrastructural analyses. The crossed-lamellar shell layers of V. verrucosa and C. chione exhibited hierarchical organizations very similar to those of the Glycymerididae. The ultrastructural temperature proxy can therefore be applied to crossed-lamellar shells of bivalves from a wide range of coastal settings, preferably in ontogenetically young shell portions.

Stable isotope ratios in patelloid limpets of the genus Patella have been established as proxies for coastal environmental change at sub-monthly resolution along the eastern North Atlantic and Mediterranean Sea. Nacella deaurata (Gmelin, 1791) and N. magellanica (Gmelin, 1791) are common intertidal species of patelloid limpets inhabiting the coast of Tierra del Fuego, Argentina/Chile and are commonly found in Holocene archaeological deposits. Here, we examine oxygen and carbon isotope ratios (δ18Oshell and δ13Cshell, respectively) of modern specimens of N. deaurata and N. magellanica to test the hypotheses that: 1) they form their shells in isotopic equilibrium with ambient water; and 2) prominent growth lines form annually. Based on growth margin analysis of δ18Oshell values, we identified a positive offset of 1.3±0.4? (N. deaurata) and 1.3±0.3? (N. magellanica) from expected equilibrium, similar to other patelloid limpets. Because the offset is relatively consistent between observed and expected values, it can be taken into account to reliably reconstruct growth temperature. Seawater temperature estimated from oxygen isotope time series data falls within the observed range. Thus, N. deaurata and N. magellenica shells serve as reliable proxy archives of seasonal variation in coastal seawater temperature. Time series of δ13C shell values do not vary seasonally in all shells; hence, the influence on its variation requires further study. The timing of prominent growth lines contextualized by the δ18Oshell time series form twice a year and therefore cannot be used to estimate lifespan. Future isotopic analysis of archaeological Nacella shells can potentially provide much needed information about Holocene climate change at sub-monthly resolution from high-latitude South American locations, and contribute to our understanding of human behavior and human-climate interactions. Fil: Nicastro, Adam.. University Of North Carolina At Chapel Hill; Estados Unidos Fil: Surge, Donna.. University Of North Carolina At Chapel Hill; Estados Unidos Fil: Briz Godino, Ivan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Alvarez, Myrian Rosa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Schöne, Bernard ,R.. Universidad Johannes Gutenberg; Alemania Fil: Bas, Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Universidad de Barcelona; España

International audience; Records of ocean/atmosphere dynamics over the past centuries are essential to understand processes driving climate variability. This is particularly true for the Northwest Atlantic which is a key region with an essential role in global climate regulation. Over the past two decades, coralline red algae have been increasingly used as environmental and climatic archives for the marine realm and hold the potential to extend long-term instrumental measurements. Here, we investigate the possibility to extract climate and environmental information from annual growth patterns and geochemical composition of the coralline red algae, Clathromorphum compactum, from Saint-Pierre & Miquelon (SPM), a French archipelago southwest of Newfoundland. However, measurements of C. compactum growth trends is challenging due to difficulties in identifying annual growth lines directly. So far, growth pattern investigations were commonly performed based on geochemical data of coralline calcite matrix. Nonetheless, this method is expensive and therefore prevents from analyzing a large number of specimens that would be representative of the population. For this reason, we enhanced the growth line readability by staining polished sections with Mutvei's solution and performed growth analysis based on direct increment width measurements. Geochemical analyses were also carried out in order to validate the assumption that growth lines observed after staining were formed on an annual basis. Moreover, growth pattern and trace element composition were measured on multiple axes of several individuals in order to assess the intra- and inter-specimen variability and validate their use for paleoenvironmental reconstructions. Finally, relationships between the C. compactum sclerochronological records from SPM and environmental datasets covering different geographical areas allow a better knowledge of flow dynamics in the Northwest Atlantic and confirm the findings related to Arctica islandica from the same location.