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Belemnites, a group of extinct coleoid cephalopods, were important components of Mesozoic marine ecosystems. Their calcitic rostra are extensively used in biostratigraphy and geochemistry. The preservation state of the rostra is a crucial factor for the interpretation of their geochemical data. However, their preservation is difficult to assess, since no modern cephalopod forms calcitic rostra. The biomineralization process of the rostrum, which functioned as an internal skeleton, is poorly understood for most species. This also applies for the epirostrum, a late ontogenetic extension of the rostrum which is only present in some belemnite species. The primary structure and function of this character are still being debated controversially. We have investigated the microstructure, stable isotope (δ 13 C, δ 18 O), and elemental composition (Mg/Ca, Sr/Ca, Fe/Ca, Mn/Ca) of both, ortho- and epirostra of the belemnite species Neohibolites minimus (Early Cretaceous, Albian). For comparison, we studied argonauts ( Argonauta argo ). These recent octopuses build a calcitic shell. Ortho- and epirostra of N . minimus show microstructural and geochemical differences. Cathodoluminescence-microscopy and the microstructures of belemnites and argonauts indicate that blue/orange luminescent growth lines in the studied belemnites are largely a primary biomineralization phenomenon and not solely due to diagenesis. Based in part on analogy to argonaut shell, we suggest that the inner part of the belemnite epirostrum is a continuation of an originally organic apical line. The development and evolution of the epirostrum as a potential sexually selected character is discussed. Well-preserved epirostrum calcite has higher element/Ca ratios than the calcite of the orthorostrum, suggesting a vital effect affecting these values. We further found evidence for vital effects on the stable isotope signatures due to metabolic and kinetic fractionation. Our findings suggest a complex mineralization process of the studied rostra. Different microstructures with distinctive geochemical signatures occur in a single belemnite species. Vital effects played an important role in the rostrum geochemistry, complicating the application of the rostra as paleoclimatic archives. [ABSTRACT FROM AUTHOR]

Abstract: The analysis of δ13C and δ18O from whole rock and the shells of selected foraminifera (Lenticulina and Dentalina) and bairdioid ostracods from Lower Toarcian of the South Iberian Palaeomargin (Western Tethys) is presented with the aim of improving knowledge of the processes and the environmental effects of the Toarcian Oceanic Anoxic Event. In addition, isotopic data are compared with geochemical redox and palaeoproductivity proxies. The microhabitat affected δ13C values, δ13C Lenticulina generally being lower than δ13 CDentalina due to more depleted 13C values for sediment pore-water in the deep infaunal microhabitat. The lowest values of δ13C (lower part of Serpentinum Zone) happen during suboxic conditions, as indicated by redox proxies, low diversity and abundance of foraminifera and higher TOC values. The fine-grained, organic rich sediments allow for conditions favouring pore-water dissolved inorganic carbon that is depleted in 13C with respect to that of the bottom sea-water, particularly during the suboxic conditions. The δ13C of potential deep infauna (Lenticulina) reflects the oxygen restricted conditions better than shallow infauna (Dentalina) and whole sediment. Regarding δ18O, values from bulk rock present stronger fluctuations and lower values than δ18O Dentalina and δ18O Lenticulina . The stratigraphic differences between δ18O Dentalina and δ18O Lenticulina correspond to vital effects, since no important fluctuations in temperature occurred in the bottom sea-water, as deduced from the absence of peaks and stratigraphic trends in the interval studied. The δ18O values do not allow us to infer temperature changes related to the Toarcian Oceanic Anoxic Event in this part of the palaeomargin. [Copyright &y& Elsevier]

Abstract: Uranium concentrations in foraminiferal and coral skeletons track oceanic [CO3 2−] and can be useful as a proxy of ocean acidification, but this pH proxy is yet to be investigated in bivalves. Two Saxidomus giganteus shells from the industrialized Puget Sound (WA, USA) and one from the more pristine Kodiak Island (AK, USA) were sampled through ontogeny for U/Ca using laser ablation inductively coupled mass spectrometry. All three shells show a similar pattern of seasonal U/Ca cycles during the first six years of life, followed by a sharp decrease to below the detection limit for the remainder of the clams life (10–20years), consistent with a biological or ontogenic forcing (vital effect). However, analyses along a growth-line (carbonate formed at the same time) show a decrease in U/Ca from the outside of the shell toward the inside, consistent with diagenesis. Clearly U/Ca is not under environmental control in these aragonite shells, but the cause of the variability is not currently clear. [Copyright &y& Elsevier]

Abstract: 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 374year-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. 5.17mmol/mol) and Mg/Ca values (max. 0.89mmol/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, R 2 =0.41, p <0.0001, growth rate-detrended Mg/Ca data: R =−0.52, R 2 =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. [Copyright &y& Elsevier]

Land snails are widely distributed animals whose clumped isotope (∆ 47) in shell carbonates can serve as a proxy for temperature in terrestrial environments. However, it is unclear whether the ∆ 47 values of snail shells are affected by biological processes known as "vital effects." Here, we report ∆ 47 values of whole Achatina fulica snail shells cultured at different temperatures at different growth ages (samples collected monthly). In general, the mean ∆ 47 values of the snail shells decrease with higher cultivation temperature, which indicates they have potential use in reconstructing temperature changes. However, the mean reconstructed ∆ 47 temperatures (T 47) using the calibrations from Petersen et al. (2019), Bonifacie et al. (2017), and Kelson et al. (2017) are ~6 °C higher than the actual growth temperatures. Interestingly, this overestimation in T 47 disappears when applying Zhai et al.'s (2019) calibration for the Bradybaena snail. This calibration also yields good agreement between the T 47 data of all field-collected snails and their growing season temperatures. The above-mentioned phenomenon indicates the existence of the vital effect in land-snail shells. The variations in ∆ 47 with snail age and the correlations between ∆ 47 , δ18O, and δ13C values also indicate the potential influence of vital effects. Finally, we suggest that the vital effect may be explained by kinetic fractionation through CO 2 degassing associated with dehydration/dehydroxylation during the formation of snail shells. • Land snail shells may suffer from the influence of subtle vital effect. • Dehydration/dehydroxylation may cause vital effect or the depletion of Δ 47. • Land snail shell Δ 47 could reconstruct its formation temperature. [ABSTRACT FROM AUTHOR]

The common whelk, Buccinum undatum , is a commercially important gastropod found throughout the North Atlantic. One method of age and life history analysis for gastropod species is the use of oxygen isotope ratio (δ18O) measurements from their shells, which is a well-established technique for the reconstruction of historical seawater temperatures at the time of shell biomineralization. Palaeotemperature calibrations have been developed for different types of calcium carbonate as well as species-specific equations to produce the most accurate seawater temperature reconstructions. Here we investigate the four-layer internal structure of B. undatum shells and confirm an aragonite composition using Micro-Raman Spectroscopy (MRS). We then calibrate a species-specific palaeotemperature equation for this gastropod species. This was achieved through the isotopic analysis of shells from laboratory reared specimens of known provenance reared at specific seawater temperatures to produce the following: t(°C) = 14.96 (± 0.15) – 4.94 (± 0.22) x (δ18O shell – δ18O water) The calibrated equation differs significantly from previously published data derived from both aragonite and calcite. An offset of 1.04‰ (± 0.41‰) was discovered between observed δ18O Shell values and those expected under equilibrium, suggesting a species-specific vital effect. The calibrated equation was used to reconstruct accurate, high resolution historical seawater temperatures from three sites across the U.K. (Shetland, the Menai Strait and Jersey). With this new accurate calibration, both modern and fossil B. undatum shells now have the potential to be employed as high-resolution archives of recent and historical seawater temperature. • New equation accurately reconstructs seawater temperatures from 3 sites around UK. • B. undatum shells produced equation with a clear offset from previous studies. • Fast growth makes B. undatum ideal for high-resolution reconstructions. [ABSTRACT FROM AUTHOR]

Oxygen and carbon isotopes and trace-element/Ca ratios are presented for the valves of benthic ostracods Palmoconcha agilis and Loxoconcha lepida extracted from two composite sediment cores from the Black Sea shelf. The two cores together provide a complete latest Pleistocene–Holocene sedimentary record, with 16 radiocarbon-dated shells in core M02-45 and 9 in core M05-50. Results reveal environmental changes and evolution of water chemistry associated with the last reconnection of the Black Sea to the global ocean. The δ18O values in composite cores M02-45 and M05-50 exhibit ranges of ~8.0‰ and ~3.0‰, respectively; δ13C values show ranges of ~2.5‰ and ~2.0‰. There are three isotopic substages: (a) substage 1c (12.1–9.4 cal ka) represents conditions in the Neoeuxine Lake with relatively high δ13C and low δ18O, (b) substage 1b (9.4–6.3 cal ka) represents the transition from lacustrine to marine conditions with an increase in δ18O values as small amounts of Mediterranean water flowed into the Black Sea, and (c) substage 1a (6.3 cal ka to Present) represents the establishment of marine conditions like today with near-constant δ18O values and a trend of slowly increasing δ13C. Trace-element/Ca ratios show downcore trends consistent with the three isotopic substages. At ~6.3 cal ka, isotopic data and trace-element/Ca ratios exhibit a major shift, with changes in the Mg/Ca ratio suggesting an increase in water temperature from 12–14 °C to 17–19 °C. These mid-Holocene changes in ostracod-valve composition and environmental conditions coincide with the weakening of Black Sea outflow and the proliferation of marine organisms. • Ostracod trace elements record water-mass evolution in Holocene Black Sea sediments. • Neoeuxine Lake from 12.1 to 9.45 cal ka had high biological productivity & TOC preservation. • Upward increase in redox-sensitive elements at 9.40 ka marks onset of stratification. • Upward Mg/Ca & Sr/Ca increases at 6.3 ka mark sharp temperature & salinity increases. [ABSTRACT FROM AUTHOR]