Search

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.

WOS:000582677500029; International audience; Horizon scanning is an increasingly common strategy to identify key research needs and frame future agendas in science. Here, we present the results of the first such exercise for the field of sclerochronology, thereby providing an overview of persistent and emergent research questions that should be addressed by future studies. Through online correspondence following the 5th International Sclerochronology Conference in 2019, participants submitted and rated questions that addressed either knowledge gaps or promising applications of sclerochronology. An initial list of 130 questions was compiled based on contributions of conference attendees and reviewed by expert panels formed during the conference. Herein, we present and discuss the 50 questions rated to be of the highest priority, determined through an online survey distributed to sclerochronology community members post the conference. The final list (1) includes important questions related to mechanisms of biological control over biomineralization, (2) highlights state of the art applications of sclerochronological methods and data for solving long-standing questions in other fields such as climate science and ecology, and (3) emphasizes the need for common standards for data management and analysis. Although research priorities are continually reassessed, our list provides a roadmap that can be used to motivate research efforts and advance sclerochronology toward new, and more powerful, applications.

International audience; High-resolution stable-isotope ratio data (delta O-18, delta O-18) were used to study growth strategies of two bivalve species, Pecten jacobaeus (calcitic shell) and Glycymeris pilosa (aragonitic shell) from the North Adriatic Sea. The principal objectives of this study were to identify the period of the year when the growth line is formed in the shell of two target species, to identify the main growing season of these two species, to identify the environmental drivers of shell growth, and to evaluate the potential applicability of delta O-18 and delta O-18 values for the reconstruction of environmental variability. Samples were collected from the North Adriatic Sea by commercial bean trawl (P. jacobaeus, December 2013 and January 2014, N = 4) and SCUBA diver (Glycymeris pilosa, March 2016, N = 3). Samples for the oxygen (delta O-18) and carbon (delta O-18) isotope composition of the calcium carbonate were collected by drilling the outer shell layer across several annual cycles. Temporal and spatial temperature and salinity values inside the investigated area were simulated using the 3D numerical ocean model - ROMS. The delta O-18 cycles corresponded to the number of seasonal growth marks observed on the external shell surface of both target species, thereby confirming the annual periodicity of these growth patterns. In February 2012, extreme cooling of the water column accompanied by dense water formation occurred in the Adriatic Sea - an event recorded by P. jacobaeus shells. This study indicates that P. jacobaeus and G. pilosa have contrasting shell growth strategies. Pecten jacobaeus grows during winter and slows shell growth during the warmest part of the year, and thereby may be an interesting archive for winter conditions. Due to its longevity and continuous growth during the warmest part of the year, G. pilosa is a promising archive for the reconstruction of summer seawater temperatures.

WOS:000426027100014; Seasonal shell growth patterns were analyzed using the stable oxygen and carbon isotope values of live-collected specimens of the bivalve Callista chione from two sites in the Adriatic Sea (Pag and Cetina, Croatia). Micromilling was performed on the shell surface of three shells per site and shell oxygen isotopes of the powder samples were measured. The timing and rate of seasonal shell growth was determined by aligning the delta O-18(shell)-derived temperatures so that the best fit was achieved with the instrumental temperature curve. According to the data, shells grew only at very low rates or not at all during the winter months, i.e., between January and March. Shell growth slowdown/shutdown temperatures varied among sites, i.e., 13.6 degrees C at Pag and 16.6 degrees C at Cetina, indicating that temperature was not the only driver of shell growth. Likely, seasonal differences in seawater temperature and food supply were the major component explaining contrasting growth rates of C. chione at two study sites. Decreasing shell growth rates were also associated with the onset of gametogenesis suggesting a major energy reallocation toward reproduction rather than growth. These results highlight the need to combine scier-ochronological analyses with ecological studies to understand life history traits of bivalves as archives of environmental variables.

International audience; Food sources of the European abalone Haliotis tuberculata throughout its life cycle are still to be clarified in nature. A novel non-destructive method of digital shell color analysis to reveal the diets of European abalone (ormer) was developed in this study. The method was calibrated using ormers reared under experimental conditions in North Western Brittany in 2012 and fed a controlled monospecific diet to define the shell hues associated with various macroalgae (i.e., Rhodophyta, Chlorophyta, and Phaeophyta). General food preferences were established by comparing the shell hue of wild adult ormers and experimental adult ormers. Shell hue corresponds to the color tint in the HSL color space measured on digital pictures of the shell. Experimentally, shell hue values differed according to treatment, with the most yellow-green hue (72°) for ormers fed Saccharina sp. and the coral hue (25°) for ormers fed Palmaria palmata. High variation in shell color of wild ormers was observed according to the sampling site and/or ontogeny. The diet of wild ormers may be related to the abundance of different drifting algae in their respective habitats. Thus, this non-destructive and easy-to-use technique appears to be a promising tool for determining the diet of Haliotis species and, perhaps, other herbivorous mollusks.

Longevity of bivalves has been an intriguing issue, especially for those species of interest for human consumption. Reliable age and growth estimates often require the combination of several methods. In this study, we analyzed changes in shell structure including ridges on the external shell surface and growth lines observed in acetate peel replicas of shell sections of the European date mussel Lithophaga lithophaga, as well as the oxygen and carbon isotope values (δ18O and δ13C) of the shell. High variations in growth rates between individuals were noted. Ontogenetic ages of analyzed shells varied from 10 to 54 years (30.6–93.6 mm). According to results of generalized von Bertalanffy growth function, L∞ was 107.6 mm, and k was 0.03 year−1. δ18O results strongly suggest that growth ridges visible on the external shell surface of L. lithophaga are formed annually. The δ18O values ranged from −0.2 to 2.7 ‰ ( $$\bar{x} = 1.15 \pm 0.72$$ ‰), which equates to a temperature range of 13 °C. The reconstructed seawater temperatures (Tδ18Oshell) ranged between 12 and 25 °C, a range in good agreement with measured temperature. Stable carbon isotope values decreased through ontogeny and ranged between −2.05 and 2.32 ‰ ( $$\bar{x} = 0.01 \pm 0.89$$ ‰). Results of this study provide the first stable isotope data for L. lithophaga shells and show the potential of this species as a geochemical sclerochronological archive.

International audience

Biogeochemical and growth increment analyses show contrasting seasonal patterns of butter clam collection and rates of harvest intensity between archaeological shell midden sites from the Dundas Islands archipelago and the mainland coast in Prince Rupert Harbour, northern British Columbia. Growth increment analysis shows more intensive clam harvest in the Dundas Islands in comparison to the residential sites in Prince Rupert Harbour. Stable oxygen isotope analysis shows multi-seasonal collection of clams in the Dundas Islands and a more seasonally specific emphasis in Prince Rupert Harbour. Comparison of these results to those of similar studies in the Namu region on the central coast of British Columbia provides a basis for broader regional understanding of variation in shellfish harvesting intensity and seasonality on the Pacific Northwest Coast.

article i nfo To analyze environmental changes and the seasonality of shell collection in British Columbia during the Ho- locene, oxygen isotopes were measured from modern and archeological (1337-7438 cal yr BP) shells of the butter clam Saxidomus gigantea. 1697 discrete isotope samples were taken from two modern and 27 arche- ological shells with a high temporal resolution (sub-seasonal up to daily). Archeological shells were collected from five shell midden sites on the Dundas Islands Group, northern British Columbia, Canada. The oxygen iso- tope data reveal clear annual cycles, with the most positive δ 18 Oshell values occurring during the cold season (slower growth, annual growth line formation) and the most negative δ 18 Oshell values during the warm sea- son (period of faster growth). Whereas the most positive δ 18 Oshell values remained relatively constant throughout the Holocene, the warm season δ 18 Oshell values reflected considerable variability. Summer values observed in the early and late Holocene became approximately 1‰ more negative around 2500-3000 and 5500-6000 BP, implying lower salinity during the Mid-Holocene. Variations in the oxygen isotopic composi- tion of marine shells reflect changes in temperature and salinity. Such large changes in δ 18 Oshell are unlikely being caused by temperature changes alone. Furthermore, the large annual δ 18

Shells of intertidal bivalve mollusks contain sub-seasonally to interannually resolved records of temperature and salinity variations in coastal settings. Such data are essential to understand changing land-sea interactions through time, specifically atmospheric (precipitation rate, glacial meltwater, river discharge) and oceanographic circulation patterns; however, independent temperature and salinity proxies are currently not available. We established a model for reconstructing daily water temperatures with an average standard error of ∼1.3 °C based on variations in the width of lunar daily growth increments of Saxidomus gigantea from southwestern Alaska, United States. Temperature explains 70% of the variability in shell growth. When used in conjunction with stable oxygen isotope data, this approach can also be used to identify changes in past seawater salinity. This study provides a better understanding of the hydrological changes related to the Alaska Coastal Current (ACC). In combination with δ18Oshell values, increment-derived temperatures were used to estimate salinity changes with an average error of 1.4 ± 1.1 PSU. Our model was calibrated and tested with modern shells and then applied to archaeological specimens. As derived from the model, the time interval of 988–1447 cal yr BP was characterized by ∼1–2 °C colder and much drier (2–5 PSU) summers. During that time, the ACC was likely flowing much more slowly than at present. In contrast, between 599–1014 cal yr BP, the Aleutian low may have been stronger, which resulted in a 3 °C temperature decrease during summers and 1–2 PSU fresher conditions than today; the ACC was probably flowing more quickly at that time. The shell growth–temperature model can be used to estimate seasonal to interannual salinity and temperature changes in freshwater-influenced environments through time.

The ability of the ocean to absorb carbon dioxide is likely to be adversely affected by recent climate change. However, relatively little is known about the spatiotemporal variability in the oceanic carbon cycle due to the lack of long-term, high-resolution dissolved inorganic carbon isotope ( δ 13 C DIC ) data, especially for the temperate North Atlantic, which is the major oceanic sink for anthropogenic CO 2 . Here, we report shell carbon isotope values ( δ 13 C shell ), a potential proxy for δ 13 C DIC , of old-grown specimens of the long-lived bivalve mollusk, Arctica islandica . This paper presents the first absolutely dated, annually resolved δ 13 C shell record from surface waters of the North Atlantic (Iceland, Gulf of Maine) covering the time interval between 1753 and 2003. According to our results, the δ 13 C shell data were unaffected by trends related to ontogenetic age. However, the shell carbonate was precipitated with a constant offset from expected equilibrium by − 1.54 to − 2.7 ± 0.2‰ corresponding to a 6.2 to 10.8 ± 0.8% contribution of respiratory CO 2 (− 25‰). The offset did not appear to vary through the lifetime of individual specimens and among specimens. Therefore, the δ 13 C shell data of this species can very likely be used as a measure of δ 13 C DIC . Furthermore, shell stable carbon isotope chronologies exhibited habitat-specific differences and a significant inter-annual and decadal variability related to the natural carbon cycle. In addition, a distinct negative δ 13 C shell shift was found reflecting the oceanic Suess effect, i.e. the admixture of anthropogenic CO 2 . However, this shift only occurred after the early 1920s when a major climate regime shift led to a northward movement of the oceanic Polar Front in the Nordic Seas and a large-scale reorganization of atmospheric and oceanic currents in the North Atlantic. This likely resulted in a reduced admixture of cold Polar water onto the North Icelandic shelf (through the East Iceland Current) and the Gulf of Maine (through the Labrador Current) with an increased volume of warmer, isotopically well-equilibrated Atlantic waters. Our shell-based δ 13 C DIC proxy record provides the basis to quantitatively assess natural and anthropogenically induced patterns of carbon uptake in the North Atlantic.

International audience; The Sr/Ca and Mg/Ca ratios of many biogenic skeletons provide useful paleotemperature estimates. As yet however, it has remained largely impossible to obtain such information from bivalve shells. In the present study, metal-to-calcium values in the hinge plate (aragonite, outer shell layer) of four ontogenetically old (85 to 374 year-old) specimens of the long-lived bivalve, Arctica islandica, were measured on a LA-ICP-MS. The shells were collected alive in 1868, 1986 and 2003 from three different localities around Iceland. With increasing ontogenetic age and decreasing growth rate, a distinct trend toward increasing Sr/Ca (max. 5.17 mmol/mol) and Mg/Ca values (max. 0.89 mmol/mol) and greater variance were observed. Three potential explanations for these trends include a reduced capacity for element selection due to cell ageing, changing metabolism and/or a relative increase in the number of organic-rich (= Mg-rich) and organic-poor (= Sr-rich) shell portions through ontogeny. Partition coefficients however, remained far below 1, indicating that physiology exerted a strong control over the element partitioning between the shells and the ambient water. After mathematical elimination of these vital effects, residuals exhibited a highly significant negative correlation (e.g., age-detrended Sr/Ca data: R = − 0.64, R2 = 0.41, p < 0.0001, growth rate-detrended Mg/Ca data: R = − 0.52, R2 = 0.27, p < 0.0001) with sea surface temperature. These results are in good agreement with results obtained from the precipitation of abiogenic aragonite. The results of the present study can help to develop new techniques to extract environmental signals from the metal-to-calcium ratios of bivalve shells.

International audience; The queen conch, Strombus gigas, is an important fisheries resource in the Western Tropical Atlantic. In order to maintain harvesting success, improve fisheries management and contribute to mariculture pursuits, a detailed understanding of the life history traits of this species is required. Traditionally, this has been achieved by tedious and time-consuming long-term field observations. This study presents a highly versatile and rapid technique to estimate the timing and rate of shell growth based on sclerochronology. The Belizean S. gigas specimens (N = 2) from the offshore atoll, Glovers Reef, reached their final shell size (maximum shell height: 22.7 and 23.5 cm, respectively; completed formation of the flared lip) after only two years. However, seasonal growth rates varied considerably. Shells grew up to 6 mm d−1 during spring (April-June) and fall (September-November) but only 1 to 2 mm d−1d uring July and August. Furthermore, shell growth ceased between December and March. Fastest shell growth occurred nearly contemporaneously with times of maximum precipitation which probably resulted in increased food availability. Slowest shell growth however, occurred during times of reduced rainfall and reduced riverine runoff, i.e. during times of reduced food supply. Sea-water temperature apparently did not exert a major control on shell growth. Notably, the slow winter growth was marked by a distinct purple-colored growth line in the cross-sectioned flared lip. Formation of a second major growth line (brown) fell together with the main reproduction period (late October/early November). Shell microgrowth patterns potentially represent daily or semidiurnal periods but cannot be used to assign exact calendar dates to each shell portion, because they were not visible across the entire cross-section of the whorl. Also, the protruding spines developed on the outer shell surface do not function as time gauges. The time represented by the shell portion between consecutive spines varies greatly from 1 to 72 days. Sclerochronology can potentially facilitate maricultural strategies and aid in site pre-testing and selection to grow S. gigas.

Annual growth increments were examined from shells of the ocean quahog (Arctica islandica L.) from northwest Norway and from tree-ring samples of the Scots pine (Pinus sylvestris L.) from nearby coastal areas. The reconstructed annual growth increments were used to compare growth variability in marine and terrestrial ecosystems. Spatiotemporal comparison of the growth records showed statistically significant correlation during the 19th century A.D., indicative of ecosystem-independent response to pre-anthropogenic climate variations. Geographical correlation between marine and terrestrial records was only observed at the local scale. Years with particularly low winter or high summer North Atlantic Oscillation (NAO) indices showed the best synchronization of marine and terrestrial growth. Despite strong correlation during historical time, our palaeoecological evidence suggests that marine and terrestrial ecosystems may show dissimilar growth reaction to recently observed positive winter-NAO phases.

Muschelschalen eignen sich hervorragend für raumzeitlich hochaufgelöste Paläoumweltrekonstruktionen. Umweltbedingungen der Vergangenheit können aus dem Schalenzuwachs und den stabilen Sauerstoff- und Kohlenstoffisotopenverhältnissen rekonstruiert werden, welche Archive für Temperatur, Süßwassereintrag und Primärproduktivität darstellen. Das Ziel dieser Doktorarbeit besteht darin, holozäne Klima- und Umweltschwankungen im nordpazifischen Sektor mit einer hohen räumlichen und zeitlichen Auflösung mittels Muschelschalen zu rekonstruieren. Diese Arbeit fokussiert sich dabei auf verschiedene holozäne Zeitabschnitte und mehrere Regionen im Nordpazifik, darunter Japan, Alaska (AK), Britisch-Kolumbien (BC) und Washington, welche vom Monsun, der Pazifischen Dekadischen Oszillation (PDO) und der El Niño/Southern Oscillation (ENSO) beeinflusst werden. Derartig hochauflösende Proxydaten aus dem marinen Bereich der mittleren und hohen Breiten sind jedoch selten. Somit trägt diese Arbeit zur Optimierung und Verifikation von Klimamodellen bei. Bevor Muschelschalen allerdings zur Umweltrekonstruktion und in Studien zur Saisonalität verwendet werden können, müssen life-history-Eigenschaften untersucht werden, um die geochemischen Daten zeitlich anzuordnen und zu interpretieren. Solche Kalibrierungsstudien sind notwendig, um die Nutzbarkeit ausgewählter Muschelarten als Paläoklimaarchive zu untersuchen. Im Fokus dieser Arbeit stehen zwei Muschelarten: die kurzlebige Buttermuschel Saxidomus gigantea und die langlebige Elefantenrüsselmuschel Panopea abrupta. Verschiedene Schalenlagen von P. abrupta wurden sklerochronologisch und sauerstoffisotopisch untersucht, um die Eignung dieser Art als Klimaarchiv zu prüfen. Die jährlichen Inkrementbreiten sind im Schalenwirbel klar erkennbar und sollten dort gemessen werden. Eine verlässliche Rekonstruktion von Paläotemperaturen kann nur durch die ausschließliche Beprobung der äußeren Schalenlage von mehreren kontemporären Muschelschalen erreicht werden. Eine detaillierte Untersuchung der life-history-Eigenschaften (z.B. Timing der Wachstumslinien, Dauer der Wachstumssaison und Wachstumsraten) und der stabilen Isotopenverhältnisse erfolgte für rezente S. gigantea Schalen aus AK und BC. Des Weiteren wurde ein Wachstums-Temperatur-Modell basierend auf S. gigantea Schalen aus AK aufgestellt, welches ein besseres Verständnis der hydrologischen Veränderungen der Strömung entlang der Küste Alaskas (Alaska Coastal Current, ACC) bietet. Dieser Ansatz erlaubt die unabhängige Messung von Wassertemperatur und Salinität aus Variationen in der Breite der Tagesinkremente in S. gigantea. Der Schalenzuwachs ist bis zu 70% temperaturgesteuert. Das Modell wurde mit rezenten Muschelschalen kalibriert und getestet und dann auf archäologische Schalen angewandt. Die Sommer in der Zeit zwischen 988 und 1447 Jahren vor heute waren kälter (~1-2°C) und viel trockener (2-5 PSU) und der ACC floss wahrscheinlich viel langsamer als heute. Im Gegensatz dazu waren die Sommer zwischen 599-1014 Jahren vor heute kälter (bis zu 3°C) und frischer (1-2 PSU) als heute. Das Aleutentief war wahrscheinlich stärker zu dieser Zeit und der ACC floss voraussichtlich schneller., Bivalve mollusk shells are useful tools for multi-species and multi-proxy paleoenvironmental reconstructions with a high temporal and spatial resolution. Past environmental conditions can be reconstructed from shell growth and stable oxygen and carbon isotope ratios, which present an archive for temperature, freshwater fluxes and primary productivity. The purpose of this thesis is the reconstruction of Holocene climate and environmental variations in the North Pacific with a high spatial and temporal resolution using marine bivalve shells. This thesis focuses on several different Holocene time periods and multiple regions in the North Pacific, including: Japan, Alaska (AK), British Columbia (BC) and Washington State, which are affected by the monsoon, Pacific Decadal Oscillation (PDO) and El Niño/Southern Oscillation (ENSO). Such high-resolution proxy data from the marine realm of mid- and high-latitudes are still rare. Therefore, this study contributes to the optimization and verification of climate models. However, before using bivalves for environmental reconstructions and seasonality studies, life history traits must be well studied to temporally align and interpret the geochemical record. These calibration studies are essential to ascertain the usefulness of selected bivalve species as paleoclimate proxy archives. This work focuses on two bivalve species, the short-lived Saxidomus gigantea and the long-lived Panopea abrupta. Sclerochronology and oxygen isotope ratios of different shell layers of P. abrupta were studied in order to test the reliability of this species as a climate archive. The annual increments are clearly discernable in umbonal shell portions and the increments widths should be measured in these shell portions. A reliable reconstruction of paleotemperatures may only be achieved by exclusively sampling the outer shell layer of multiple contemporaneous specimens. Life history traits (e.g., timing of growth line formation, duration of the growing season and growth rates) and stable isotope ratios of recent S. gigantea from AK and BC were analyzed in detail. Furthermore, a growth-temperature model based on S. gigantea shells from Alaska was established, which provides a better understanding of the hydrological changes related to the Alaska Coastal Current (ACC). This approach allows the independent measurement of water temperature and salinity from variations in the width of lunar daily growth increments of S. gigantea. Temperature explains 70% of the variability in shell growth. The model was calibrated and tested with modern shells and then applied to archaeological specimens. The time period between 988 and 1447 cal yrs BP was characterized by colder (~1-2°C) and much drier (2-5 PSU) summers, and a likely much slower flowing ACC than at present. In contrast, the summers during the time interval of 599-1014 cal yrs BP were colder (up to 3°C) and fresher (1-2 PSU) than today. The Aleutian Low may have been stronger and the ACC was probably flowing faster during this time.

International audience; Interannual and intra-annual variations in lithium-to-calcium ratio were investigated with high temporal resolution in the aragonitic outer shell layer of juvenile Arctica islandica (Mollusca; Bivalvia) collected alive in 2006 off northeast Iceland. Li/Cashell ranged between 7.00 and 11.12 µmol mol-1 and presented well-marked seasonal cycles with minimum values recorded at the annual growth lines; a general pattern was a progressive increase in Li/Cashell from March to May, followed by a plateau in June and a decrease down to minimum values in July-August. Li/Cashell was correlated with d18Oshell-derived temperature, but the strength of this relationship was weak (r2 < 0.25 and p < 0.05). It covaried significantly with microgrowth increment width and with the discharge from one of the closest rivers. Seasonal variations of Li/Cashell in A. islandica may most likely be explained (1) by calcification rate and/or (2) by significant river inputs of Li-rich silicate particles flowing to the sea as soon as snow melts. In the first case, Li/Cashell may be a useful proxy for addressing seasonal variations of growth rate in bivalves that lack discernable microgrowth patterns. Abrupt decreases of Li/Cashell may, in turn, help identify growth retardations due to harsh environmental conditions. Alternatively, if Li/Cashell variations are linked to particulate Li inputs by rivers, this could be a new proxy for the intensity of mechanical weathering of Icelandic basalts, with interesting perspectives for the reconstruction of frequency and intensity of past jökulhlaups (subglacial outburst floods). Further works, including experimental studies, are needed to test these hypotheses.