Shell δ13C Values Research Articles

Stable carbon and oxygen isotope-based sclerochronology of bivalve mollusk shells from the Upper Cretaceous (upper Campanian) Coon Creek Formation in Tennessee, USA: Implications for paleoecology and paleoenvironment

Stable carbon and oxygen isotope-based sclerochronology was carried out on well-preserved fossil shells of bivalve mollusks Crassatella vadosa and Cucullaea vulgaris from the Upper Cretaceous (upper Campanian) Coon Creek Formation in Tennessee, USA, to reconstruct their life-history traits and sedimentary settings on an intra-annual time scale. The δ13CShell values along with the shell growth showed the cyclic variation with downward convex to lower value, likely reflecting the seasonal cycle of ambient seawater dissolved inorganic carbon (DIC) or metabolism of the bivalve or both. The δ13CShell cycles were largely associated with the strong growth disturbance lines, supporting hypothesis that the growth lines were formed annually. We estimated the ages of the shells based on both δ13C cycle or the growth cessation line. The modeled relationship between age and shell growth showed that Cr. vadosa and Cu. vulgaris grew up to about 40 mm at 7 years old and about 65 mm at 10 years old, respectively. The paleotemperatures estimated from the δ18OShell profiles of the examined specimens ranged from 16.2 °C to 24.2 °C and from 18.8 °C to 27.0 °C when assuming the bottom seawater δ18O to be −1.00‰ and −0.46‰ (VSMOW), respectively, and showed no clear seasonal cycle. The bottom seawater temperatures reconstructed from the specimens of the two bivalve species were lower than the near-surface seawater temperatures (29.0–30.6 °C) estimated from the planktic foraminiferal δ18O. We inferred that the benthic bivalve habitat of the Coon Creek Formation was at least 10 m or deeper below the thermocline.

Stable carbon isotopes in scallop shells: A proxy of Antarctic sea-ice persistence

Sea ice is fundamental to global climate and its multiannual persistence or seasonal absence shapes Antarctic marine ecosystems. With sea ice in rapid decline in the Southern Ocean, it is imperative to understand its variability prior to satellite data. The Antarctic scallop Adamussium colbecki has a broad geographic distribution and long fossil history in the Southern Ocean, and its shells could be ideal bioarchives for sea ice with the potential to resolve subannual sea-ice dynamics over multiple years or decades. Here, we evaluate stable isotopes of carbon in A. colbecki shells from two sites on western McMurdo Sound. Each site maintains stable, frigid seawater temperatures, but they differ in sea-ice duration. Explorers Cove has semi-permanent multiannual sea ice, whereas Bay of Sails has annual sea ice that breaks out every year. Our results indicate that seasonal variation in δ13Cshell values may proxy sea-ice persistence. Scallops living under annual sea ice — adults from Bay of Sails and juveniles collected during a fortuitous recent sea ice breakout at Explorers Cove — had higher δ13Cshell values during summer growth than winter growth. Scallops living under multi-annual sea ice had no difference in δ13Cshell values between winter and summer growth. We posit that phytoplankton blooms leverage the seasonal δ13C values of the dissolved inorganic carbon under ice-free conditions, which is in turn recorded in δ13Cshell values and that A. colbecki shells could be used to understand past variability in sea-ice persistence in coastal Antarctica.

Mytilus galloprovincialis shell growth – Insights from shell geochemistry

Despite the wide geographic distribution of mussels and their importance in fisheries and aquaculture, understanding of temporal and spatial variations of their growth is still limited. This can be, at least partly, attributed to the lack of distinct growth lines in their shells. Our study uses geochemical properties of shells, particularly oxygen (δ18Oshell) and carbon (δ13Cshell) stable isotope values, to reconstruct mussel growth. Mytilus galloprovincialis specimens were collected from two of the most important bivalve aquaculture sites in the eastern Adriatic - Krka River estuary and Mali Ston Bay. The first site has variable environmental conditions, influenced mainly by the Krka River, resulting in a strong temperature and salinity gradient along the estuary. In contrast, Mali Ston Bay is a relatively shallow enclosed bay with more stable conditions. Samples for δ18Oshell and δ13Cshell analysis were acquired by manual microdrilling cross-sectioned shells from three similar sized shells from each site. In addition, analysis of elemental profiles (Mg/Ca, Sr/Ca, and Ba/Ca) in shells from the Krka River estuary was conducted using laser ablation ICPMS. Temperature and salinity values were obtained for each site through research and monitoring projects and used to calculate predicted δ18Oshell values. By aligning the measured δ18Oshell data along the predicted δ18Oshell curve, it was possible to reconstruct the timing and rate of seasonal shell growth. Results show that M. galloprovincialis shell deposition slows down and/or ceases during high temperature and low salinity periods. Specimens from the Krka River estuary had faster shell growth rates and were characterised by higher δ13Cshell values. Mg/Ca profiles of M. galloprovincialis specimens from the Krka River estuary, confirm growth periodicity data obtained by δ18O analysis. Ba/Ca peaks were also discussed by comparison with δ13C time-series and environmental data. Results have potential applications in fisheries studies as well as in palaeoecology and palaeoceanography research.

Carbon isotope values of hazelnut shells: a new proxy for canopy density

Hazel (Corylus avellana) has been abundant in the vegetation of northern and central Europe since the early Holocene and has provided food and materials for humans ever since. Here we use stable carbon isotope (δ13C) values of hazelnut shells to infer woodland openness based on the premise of the “canopy effect”. It is well established that plants growing in dense, shaded forests have lower carbon isotope (δ13C) values than plants growing in open areas. By measuring δ13C values in hazelnuts collected from trees growing in different levels of light intensity, we show that the canopy effect is preserved in hazelnuts and that their δ13C values can be used to infer woodland openness in the past. We apply the method to hazelnuts recovered from sites dated to between the Mesolithic and Iron Age (c. 7000 BCE−1000 CE) in southern Sweden. Our results show that the nuts dated to the Mesolithic were harvested from hazels growing in a range of closed to open settings while nuts from subsequent periods were harvested from progressively more open environments. Given the abundance of hazelnuts recovered from many archaeological contexts, this method has the potential to reconstruct the microhabitats exploited by humans in the past and explore the impact of humans on their environment.

Late glacial–Younger Dryas climate in interior Alaska as inferred from the isotope values of land snail shells

AbstractThe isotope values of fossil snail shells can be important archives of climate. Here, we present the first carbon (δ13C) and oxygen (δ18O) isotope values of snail shells in interior Alaska to explore changes in vegetation and humidity through the late-glacial period. Snail shell δ13C values were relatively consistent through the late glacial. However, late-glacial shell δ13C values are 2.8‰ higher than those of modern shells. This offset is best explained by the Suess effect and changes in the δ13C values of snail diet. Snail shell δ18O values varied through the late glacial, which can be partially explained by changes in relative humidity (RH). RH during the snail growing period was modeled based on a published flux balance model. Results suggest a dry period toward the beginning of the Bølling–Allerød (~14 ka) followed by two distinct stages of the Younger Dryas, a wetter stage in the early Younger Dryas from 12.9 to 12.3 ka, and subsequent drier stage in the late Younger Dryas between 12.3 and 11.7 ka. The results show that land snail isotopes in high-latitude regions may be used as a supplementary paleoclimate proxy to help clarify complex climate histories, such as those of interior Alaska during the Younger Dryas.

Implications of submonthly oxygen and carbon isotope variations in late Pleistocene Melanopsis shells for regional and local hydroclimate in the upper Jordan River valley

AbstractMany water-stressed regions of the globe have a highly seasonal precipitation regime. However, seasonality in the past and under changing climates is little studied. Submonthly records of sclerochronological δ18O and δ13C values of Melanopsis shells from the Jordan River Dureijat archaeological site (JRD) in the upper Jordan River valley presented here document the hydrology of paleo-Lake Hula. These records were assessed for changes in seasonal hydrology in the lake and compared with modern shells collected from present-day waterbodies in northern Israel and with models of δ18Oshell. Results from shells in sediments dating from the last glacial maximum (LGM) to the Bølling-Allerød imply changes in waterbody size that qualitatively parallel changes in the late Pleistocene Lake Lisan levels; Hula Lake was well buffered when Lake Lisan stood at a high stand and poorly buffered when water levels were lower. Furthermore, data from shells dated to the LGM suggest inflowing water with lower δ18O values than local rainfall, providing evidence for a greater proportion of snow in the catchment than today. Reconstruction of water δ18O and mixing-model calculations suggest that snowmelt contribution to spring water during the LGM may have been more than twice the amount in the modern-day catchment.

Symbiotic Zooxanthellae Drive the δ13C Changes of Tridacna gigas Shell in the Southern South China Sea

AbstractThe carbon isotope (δ13C) in marine biogenic carbonate is a valuable tool for comprehending the marine carbon cycle. However, the absence of monthly resolved δ13C records before the instrumental era (since 1850) hinders us to fully understand the global carbon cycle. In this study, we present a δ13C record from a modern Tridacna gigas shell (δ13Cshell) collected from the southern South China Sea (SCS) with an average resolution of ∼10 days. The δ13C record illustrates seasonal and interannual cycles which are superimposed by long‐term decreasing trend. We investigate the environmental controls influencing the δ13Cshell on different time scales. We suggest that more positive δ13Cshell values observed during the juvenile stage (first 8–10 years), which correspond to a high growth rate, can be attributed to 13C enrichment of the internal dissolved inorganic carbon pool. This resulted from the exponential increase of symbiotic zooxanthellae, and preferential 12C sequestration by the accelerated buildup of productive tissues. On the interannual time scale, changes in δ13Cshell were likely affected by both internal (vital effect) and external processes (sea water δ13C), as well as being disturbed by the super El Niño‐La Niña event. Seasonal changes of δ13Cshell were mainly dominated by the intensity of photosynthesis and respiration of symbiotic zooxanthellae, which depend on the seasonal solar irradiance variations in association with precipitation and the South Asian summer monsoon. Our study sheds light on the controlling factors of δ13Cshell variations on seasonal timescale and the long‐term trend, providing insight into the carbon cycle over geological history.

100 k.y. pacing of the East Asian summer monsoon over the past five glacial cycles inferred from land snails

Abstract The effects of orbital forcing on the East Asian summer monsoon (EASM) after the mid-Pleistocene transition are controversial. Chinese cave δ18O records only show low-latitude ∼20 k.y. cycles, while pedogenic proxy records from Chinese loess are dominated by highlatitude 100 k.y. cycles. This discrepancy may result from the multicomponent origin of proxies, particularly for pedogenic signals in loess deposits, where the primary climatic signals are modified by pedogenic smoothing, leaching, and changes in sedimentation rate, and the latter are also being forced by 100 k.y. cycles. We present an EASM record spanning the past 470 k.y. from the central Chinese Loess Plateau based on the δ13C values of land snail shells (δ13Cshell), which eliminates the influence of the above processes and exclusively records the local past EASM precipitation. The δ13Cshell record is dominated by the 100 k.y. cycle, with more depleted values during interglacials compared to glacials. At the end of marine isotope stage (MIS) 11, δ13Cshell-based precipitation remained at an interglacial level following the MIS 11 super-interglacial climate in the Northern Hemisphere, although a glacial period had commenced on a global basis. Overall, our δ13Cshell record is highly coupled with high-northern-latitude ice-volume variations, possibly supporting the high-latitude forcing of the EASM.

Looking upstream with clumped and triple oxygen isotopes of estuarine oyster shells in the early Eocene of California, USA

Abstract The δ18O of carbonate minerals that formed at Earth's surface is widely used to investigate paleoclimates and paleo-elevations. However, a multitude of hydrologic processes can affect δ18O values, including mixing, evaporation, distillation of parent waters, and carbonate growth temperatures. We combined traditional carbon and oxygen isotope analyses with clumped (Δ47) and triple oxygen isotopes (Δ′17O) analyses in oyster shells (Acutostrea idriaensis) of the Goler Formation in southern California (USA) to obtain insights into surface temperatures and δ18O values of meteoric waters during the early Eocene hothouse climate. The Δ47-derived temperatures ranged from 9 °C to 20 °C. We found a correlation between the δ18O of growth water (δ18Ogw) (calculated using Δ47 temperatures and δ18O of carbonate) and the δ13C values of shells. The Δ′17O values of shell growth waters (0.006‰–0.013‰ relative to Vienna standard mean ocean water–standard light Antarctic precipitation [VSMOW-SLAP]) calculated from Δ′17O of carbonate (−0.087‰ to −0.078‰ VSMOW-SLAP) were lower than typical meteoric waters. These isotopic compositions are consistent with oyster habitation in an estuary. We present a new triple oxygen isotope mixing model to estimate the δ18O value of freshwater supplying the estuary (δ18Ofw). The reconstructed δ18Ofw of −11.3‰ to −14.7‰ (VSMOW) is significantly lower than the δ18Ogw of −4.4‰ to −9.9‰ that would have been calculated using “only” Δ47 and δ18O values of carbonate. This δ18Ofw estimate supports paleogeographic reconstructions of a Paleogene river fed by high-elevation catchments of the paleo–southern Sierra Nevada. Our study highlights the potential for paired Δ47 and Δ′17O analyses to improve reconstructions of meteoric water δ18O, with implications for understanding ancient climates and elevations.

Nitrogen Isotope Sclerochronology—Insights Into Coastal Environmental Conditions and Pinna nobilis Ecology

Pinna nobilis is a large bivalve endemic to the Mediterranean Sea that lives in shallow coastal areas. Due to its size and relatively fast shell growth rates, it is an interesting taxon for high-resolution study of nitrogen isotopes of carbonate bound organic matter (δ15NCBOM). In this study we tested if P. nobilis shells can be used as an indicator of the nitrogen isotope baseline of the system, if it can provide high-resolution data on environmental δ15N variability, and if the chemical properties of the shell and biomineralization process change in response to mass mortality events spreading in the Mediterranean. Shells were opportunistically collected during 2019 and 2020 by skin diving, as a part of a project on mortality monitoring, from four shallow coastal localities in the eastern Adriatic. Shell powder for δ15NCBOM analysis was collected by milling sample swaths from the internal (low-resolution) and external (high resolution) shell surface. Significant differences in δ15NCBOM, obtained from the internal shell surface, were observed between sampling localities with different anthropogenic influences, with lowest values (∼3–4‰) recorded for shells obtained from Pag Bay, and highest (∼6–8‰) for shells sampled in Lim and Kaštela Bays. High-resolution samples from the external shell surface of Pinna nobilis showed spatial and temporal variations in δ15NCBOM values, with temporal resolution of 1–3 weeks. High-resolution δ15NCBOM data obtained from the shell Kas1 corresponded to a time interval from spring 2018 to summer 2019 and had a pronounced increase of δ15NCBOM values closest to the shell margin coupled with a decrease in δ13Cshell values, indicating that this animal was experiencing stressful conditions several months prior to its death. According to our findings, δ15NCBOM values from P. nobilis shells can serve as an indicator of the isotopic baseline of the ecosystem potentially as a powerful tool to study bivalve physiology.

Small Size Gastropod Fauna from the Matli Geothermal Spring, Bhagirathi Valley, Garhwal Himalaya, Uttarakhand: Ecological Implications

Abstract The occurrence of freshwater molluscs in the geothermal springs is reported by numerous workers in different parts of the world. However, reports of such occurrences in the Indian subcontinent are either scanty or are not available in the published literature. In this study, a swarm of small size gastropod community have been encountered in the vicinity of Matli geothermal spring, which is located on the right bank of the downstream Bhagirathi river in the Garhwal Himalaya in Uttarakhand, India. Gastropod samples were collected from 3 locations near the spring and water samples were collected from the spring and the river. The samples were identified as belonging to the species Lymnaea acuminata Lamarck, 1822 according to their form and habitat. The abundance, size and thickness of the snails were higher near the spring than near the Bhagirathi river. The δ18Oshell and δ13Cshell values of all the bulk samples range from – 8.2 to – 7.8‰ (VPDB) and from – 9.5‰ (VPDB) to – 6.5‰ (VPDB), respectively. Since the temperature of the geothermal spring remains constant irrespective of seasons, no significant intra-shell variation in δ18O is observed, while intra–shell δ13C values show shell shell significant variation reflecting season change. Lymnaea accuminata is originally a freshwater gastropod which is found all along the Ganga-Brahmaputra watersheds. This species prefers a habitat near the geothermal spring owing to the abundance of nutrients in spring water and other physiological factors.

Changes in Paleovegetation and Climate Seasonality in Central China Over Last Two Glacial Cycles: A Stable Isotope Perspective From Land Snails

AbstractModern investigations have shown that oxygen and carbon isotopes of land snail shells are useful indicators of climate and vegetation in monsoonal regions. However, stable isotope studies on snail fossil shells have seldom been done, and the reliability of those indicators needs further verification. Moreover, intrashell stable isotope analysis of individual snails is rather scarce, and seasonal variation in the glacial‐interglacial monsoonal climate remains unclear. Therefore, we performed δ18O and δ13C analyses on fossil shells of cold‐aridiphilous Cathaica pulveratrix and subhumidiphilous Metodontia yantaiensis from the loess section over the last two glacial cycles at the Beiyao site on the southern Chinese Loess Plateau. The δ18O values of fossil shells reflected monsoonal rainfall amounts and more rainfall during MIS3 and MIS7 than during MIS4 and MIS6. Meanwhile, the δ13C values of fossil shells indicated the relative abundance of C3/C4 plants and more C4 biomass during MIS3 and MIS7 than during MIS4 and MIS6. The δ18O and δ13C values of the two species from the same horizon are significantly different, reflecting differences in their growing season and/or physiological habits. Intrashell variations in stable isotopes showed that climatic seasonality was much stronger during the glacial periods than during the interglacials. Our findings provide an environmental background for explaining past human activities at the Beiyao site. The investigation of stone artifacts showed that ancient human activities were relatively strong during MIS3 and MIS7. During these stages, the warm and humid climate with smaller seasonal contrast was favorable for the regional expansion of human activities.

Evaluating Freshwater Mussel Shell δ13C Values as a Proxy for Dissolved Inorganic Carbon δ13C Values in a Temperate River

AbstractThe stable isotope ratio of dissolved inorganic carbon (δ13CDIC) in rivers reflects the dominant vegetation type in the surrounding watershed, rates of chemical weathering, atmospheric CO2 fluxes, and the relative rates of photosynthesis and respiration. Reconstructing past δ13CDIC values may reveal changes in these characteristics before watersheds experience land‐use change and/or climate change. This study uses freshwater mussels, Elliptio complanata, and coeval environmental data to assess how high‐resolution changes in the oxygen and carbon isotope ratios of shell carbonate (δ18Oshell and δ13Cshell, respectively) can be used as proxies of paleotemperature and paleo‐DIC in rivers. To test our hypotheses, we analyzed time‐series δ18Oshell and δ13Cshell values, δ13C values in bivalve tissues, and environmental data collected fortnightly from the Neuse River, North Carolina. Shell microsamples milled every 150 μm along the maximum growth axis represent an average of 12 ± 5 days (n = 524; excluding periods of growth cessation of >30 days), which is similar to the environmental data resolution (∼14 days). Serially sampled δ18Oshell and δ13Cshell values did not capture the full range of environmental conditions due to growth cessation during winter shutdown and extreme weather events. Low water temperature and elevated turbidity appear to be significant drivers of growth cessation. Spatial and temporal differences in the amount of metabolic carbon incorporated in the shell (∼0%–44%) likely occur due to variable mussel metabolic rates within and among study sites. Though high‐resolution δ13Cshell values did not reflect variations in δ13CDIC values, average δ13Cshell values were indicative of average δ13CDIC values in the Neuse River.

Evaluating Freshwater Mussel Shell δ13C Values as a Proxy for Dissolved Inorganic Carbon δ13C Values in a Temperate River

Evaluating Freshwater Mussel Shell δ13C Values as a Proxy for Dissolved Inorganic Carbon δ13C Values in a Temperate River

Oceanic cooling recorded in shells spanning the Medieval Climate Anomaly in the subtropical eastern North Atlantic Ocean

The Medieval Climate Anomaly (MCA; 900–1300 AD) was the most recent period of pre-industrial climatic warming in the northern hemisphere, and thus estimations of MCA signals can illuminate possible impacts of anthropogenic climate change. Current high-resolution MCA climate signals are restricted to mid- and high-latitude regions, which confounds inferences of how the MCA impacted some global/hemispheric climate mechanisms (e.g. North Atlantic Oscillation; NAO). To address this knowledge gap, we estimate seasonally-resolved sea surface temperatures (SSTs) from the oxygen isotope composition (δ18O) of serially sampled Phorcus atratus shells from archaeological sites spanning the MCA in the Canary Islands. Twelve archaeological and six modern P. atratus shells were analyzed, and archaeological shells were dated using carbonate-target radiocarbon dating. SSTs were estimated using the published aragonite-water equilibrium fractionation equation. Modern shells showed a mean SST of 20.0 ± 1.5 °C, with a seasonal amplitude of 5.3 ± 0.9 °C. Archaeological shells exhibited a mean SST of 18.2 ± 0.7 °C, with a mean seasonal amplitude of 5.5 ± 1.0 °C. Thus, shells that span the MCA in the Canary Islands recorded SSTs that were significantly cooler than the modern (P < .05), contrasting with warming estimates and model predictions elsewhere in the Northern Hemisphere. We propose that the observed cooling resulted from increased upwelling in NW Africa due to a strengthening of the prevailing westerlies and coastal winds along the African shoreline. The intensified upwelling scenario during the MCA is partially supported by in-situ carbon isotope data (δ13C) retrieved from the archaeological shells, which was compared to the δ13C values of modern shells and dissolved inorganic carbon in the ambient seawater. These results are consistent with other low-latitude temperature/precipitation anomalies associated with a positive NAO mode, suggesting a transition to a positive NAO index during the middle and late MCA that possibly extended later into the 13th century AD.

Olympia oyster, Ostrea lurida, in Puget Sound: stable isotope shell profiles as potential indicators of a changing climate

There is a need to monitor environmental changes in situ across aquatic ecosystems. Sclerochronology, a systematic biogeochemical method that assesses variations in the accretionary hard tissues of invertebrates, can be useful in studying these changes. Further studies are needed to evaluate whether an equilibrium relationship exists between seasonal annual temperature variations in bivalve shells of species with multiple geographic ranges. We present one of the first sclerochronology reports to characterize the δ18O and δ13C shell profiles of the Olympia oyster, Ostrea lurida Carpenter, 1864. We evaluated its utility as a proxy for past water temperature relating to seasonal cycles. The objectives were to: (1) assess shell δ18O and δ13C values from specimens sampled over time; and (2) evaluate whether δ18O shell profiles correlate with seasonal temperature patterns. Seven O. lurida specimens were collected, and measurements were taken across shell growth. Results from generalized linear mixed models (GLMM) showed that O. lurida produced δ18O profiles consistent with a sinusoidal time pattern. The δ18O values ranged from –2.74‰ to –1.05‰, and there was a significant third-order polynomial temporal relationship. Covariation between profiles of shell δ18O and δ13C values was observed over time. Two independently estimated measures of δ18Owater, accounting for salinity, temperature, and shell carbonate, were also positively correlated over time. Implications support the theory that O. lurida shell δ18O profiles may be in isotopic equilibrium with ambient water conditions with applications for monitoring programs.

Implications of the apparent 14C age of cultured Achatina fulica and the spatial features of 14C ages among modern land snail shells in China

It has long been known that many terrestrial snail shells are subject to the so-called “limestone effect”. However, the magnitude and impact of this effect on the δ13C values of snail shells and soft body tissue (δ13Cshell and δ13Cbody) are still unknown. In this study, Achatina fulica snails were hatched and cultured under controlled conditions and supplied with 14C-free calcium carbonate and lettuce (a C3 plant) as a calcium source and food supply, respectively. The snail shells and soft body tissues were sampled monthly for 5 months, and δ13C and radiocarbon dating analyses were conducted to trace carbon source variations at different growth stages. Our results show that the apparent 14C age of the shells and the corresponding δ13Cshell values increased progressively from the 1st to 3rd months and subsequently decreased during the 4th and 5th months. The results demonstrate for the first time that carbonate ingestion has a straightforward influence on the 14C ages and δ13C values of shells and that the “limestone effect” changes over the lifetime of snails. Moreover, the apparent 14C ages of snails sampled in the field are older than modern ages when taken from the northern carbonate region and relatively young or the same as modern ages when collected from ferralic soils. This further supports our findings from cultured snails and suggests that snail shells are good archives for radiocarbon dating purposes in southern China.Although the δ13C values of the soft body tissues of cultured snails vary synchronously with those of the shell, this seemingly common phenomenon cannot be easily explained by carbonate ingestion, as the snail bodies are of more recent origin than the shells. Atmospheric CO2 may be another candidate explaining the synchronicity between δ13Cshell and δ13Cbody, as well as the F 14C variations of snail bodies. However, it is still unclear how snails differentially incorporate carbon from different sources (e.g., carbonate and atmospheric CO2) at different growth stages, since carbon from different sources is combined in the bicarbonate pool in the hemolymph before being used by snails.

High-resolution records of growth temperature and life history of two Nacella limpet species, Tierra del Fuego, Argentina

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 δ13Cshell 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.

New insight into light-enhanced calcification in mytilid mussels, Mytilus sp., infected with photosynthetic algae Coccomyxa sp.: δ13C value and metabolic carbon record in shells

The posterior shell edge (PSE) of wild mytilid mussels that are highly infected with unicellular photosynthetic green algae Coccomyxa sp. exhibits an extra shell material (ESM). A recently proposed mechanism of ESM formation shows similarity with light-enhanced calcification (LEC), i.e., algae photosynthesis mediates low respiratory CO2 level in shell calcification site (PSE) to promote ESM precipitation. The present study evaluates if infection with algae may affect the δ13C content and metabolic carbon (CM) contribution to shells (PSE) in mussels from the Lower St. Lawrence Estuary, Québec, Canada. Environmental conditions may influence shell δ13C records. To underline possible algae photosynthesis effects, mantle, adductor muscle and shell δ13C are analyzed in infected and non-infected mussels collected from two sites with different salinities, seawater dissolved inorganic carbon (DIC) content, and hydrodynamic regimes. Shell δ13C and tissue δ13C correlate with seawater DIC and salinity. Shell δ13C values are lowest in non-infected mussels, whereas tissues δ13C values show the opposite relationship; in both cases, differences between δ13C values in non-infected and infected mussels are about 0.5‰. The percentage of CM incorporated into shell is higher (ca. 18%) for non-infected mussels than infected mussels (ca. 15%). Literature on the subject suggests that increased δ13C content and decreased %CM in shells of infected mussels must be related to algal photosynthetic activity. Our findings show that shell δ13C records permit the interpretation of ESM formation via LEC.

Glycymeris pilosa (Bivalvia) – A high-potential geochemical archive of the environmental variability in the Adriatic Sea

Due to its outstanding longevity (decades), the shallow-water bivalve Glycmeris pilosa represents a prime target for sclerochronological research in the Mediterranean Sea. In the present study, we analyzed the microgrowth patterns and the stable carbon (δ13Cshell) and oxygen (δ18Oshell) isotopes of the outer shell layer of live-collected G. pilosa specimens from four different sites along the Croatian coast, middle Adriatic Sea. Combined analysis of shell growth patterns and temporally aligned δ18Oshell data indicated that the main growing season lasts from April to December, with fastest growth rates occurring during July and August when seawater temperatures exceeded 22 °C. Slow growth in the cold season (<12 °C) coincided with the formation of winter growth lines on the outer shell surface. The growth cessation occurred in winter, but on the outer shell surface the brown summer bands are more pronounced than the winter lines. Mutvei-staining of cross-sections facilitated the recognition of the growth lines. δ13Cshell values reflect ontogenetic changes in physiology as well as seasonal changes in primary production and salinity.