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#isotope

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Public
Niels de Winter

Check out our latest #preprint in which we use a combination of #clumped and #oxygen #isotope measurements to reconstruct extreme summer temperatures experienced by #fossil #rudist bivalves from the Late #Cretaceous in Oman. All feedback is welcome!
egusphere.copernicus.org/prepr

egusphere.copernicus.orgLiving on the edge: Response of rudist bivalves (Hippuritida) to hot and highly seasonal climate in the low-latitude Saiwan site, OmanAbstract. Earth’s climate history serves as a natural laboratory for testing the effect of warm climates on the biosphere. The Cretaceous period featured a prolonged greenhouse climate characterized by higher-than-modern atmospheric CO2 concentrations and mostly ice-free poles. In such a climate, shallow seas in low latitudes probably became very hot, especially during the summers. At the same time, life seems to have thrived there in reef-like ecosystems built by rudists, an extinct group of bivalve molluscs. To test the seasonal temperature variability in this greenhouse period, and whether temperature extremes exceed the maximum tolerable temperatures of modern marine molluscs, we discuss a detailed sclerochronological (incrementally sampled) dataset of seasonal scale variability in shell chemistry from fossil rudist (Torreites sanchezi and Vaccinites vesiculosus) and oyster (Oscillopha figari) shells from the late Campanian (75-million-year-old) low latitude (3° S paleolatitude) Saiwan site in present-day Oman. We combine trace element data and microscopy to screen fossil shells for diagenesis, before sampling well-preserved sections of a Torreites sanchezi rudist specimen for clumped isotope analysis. Based on this specimen alone, we identify a strong seasonal variability in temperature of 19.2 ± 3.8 °C to 44.2 ± 4.0 °C in the seawater at the Saiwan site. The oxygen isotopic composition of the seawater (δ18Osw) varied from -4.62 ± 0.86 ‰ VSMOW in winter to +0.86 ± 1.6 ‰ VSMOW in summer. We use this information in combination with age modelling to infer temperature seasonality from incrementally sampled oxygen isotope profiles sourced from the literature, sampling multiple shells and species in the assemblage. We find that, on average, the Saiwan seawater experienced strong seasonal fluctuations in monthly temperature (18.7 ± 3.8 to 42.6 ± 4.0 °C seasonal range) and water isotopic composition (-4.33 ± 0.86 to 0.59 ± 1.03 ‰ VSMOW). The latter would strongly bias the interpretation of stable oxygen isotopes in shell carbonate without independent control on either temperature or seawater composition. Combining our seasonal temperature estimates with shell chronologies based on seasonal cyclicity in stable isotope records and daily variability in trace element data, we show that T. sanchezi rudists record temperatures during the hottest periods of the year as well as during the winters, which were characterized by cooler temperatures and enhanced influx of freshwater. Both O. figari and V. vesiculosus plausibly stopped growing during these seasonal extremes. This study aims to demonstrate how high-resolution geochemical records through fossil mollusc shells can shed light on the variability in past warm ecosystems and open the discussion about the limits of life in the shallow marine realm during greenhouse climates. Future work should apply the clumped isotope paleothermometer on incrementally sampled bio-archives to explore the upper-temperature limits experienced by calcifiers in different environments throughout geological history.
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Susan Ville

🗨️ F*ck off, ISR, the new #Isotope of the Nazis! Your entire so called parliament has been involved in #warcrimes and #CrimesAgainstHumanity - since 1948, the world is no longer interested in your sick statements! Everybody KNOWS that you are not representing the Jewish interests!

Kind greets from a #German #resistance fighter against fascists and anti-humanists!

The Hague awaits! #icj #icc #un

#Nurnberg1945 #TheHague2025

nna-leb.gov.lb/en/regional/784

Public
Niels de Winter

Exploring macroevolutionary links in multi-species #planktonic #foraminifera Mg∕Ca and stable #oxygen #isotope from 15 Ma to recent @EGU_BioGeo bg.copernicus.org/articles/22/

bg.copernicus.orgExploring macroevolutionary links in multi-species planktonic foraminiferal Mg∕Ca and δ18O from 15 Ma to recentAbstract. The ratio of the trace element Mg over Ca (Mg/Ca) and the oxygen isotopic composition (δ18O) of foraminiferal calcite are widely employed for reconstructing past ocean temperatures, although geochemical signals are also influenced by several other factors that vary temporally and spatially. Here, we analyse a global dataset of Mg/Ca and δ18O data of 59 middle Miocene to recent species of planktonic foraminifera from a wide range of depth habitats, many of which have never been analysed before for Mg/Ca. We investigate the extent to which Mg/Ca and δ18O covary through time and space and identify several sources of mismatch between the two proxies. Once the data are adjusted for long-term non-thermal factors, Mg/Ca and δ18O are overall positively correlated in a way consistent with temperature being the dominant controller through both space and time and across many different species, including deep dwellers. However, we identify several species with systematic offsets in Mg/Ca values, to which multispecies calibrations should be applied with caution. We can track the appearance of such offsets through ancestor-descendent species over the last 15 Myr and propose that the emergence of these offsets may be the geochemical expression of evolutionary innovations. We find that virtually all of the Mg/Ca- and δ18O-derived temperatures from the commonly used genera Globigerinoides and Trilobatus are within uncertainty of each other, highlighting the utility of these species for paleoceanographic reconstructions. Our results highlight the potential of leveraging information from species lineages to improve sea surface temperature reconstruction from planktonic foraminifera over the Cenozoic.
Public
arthurgessler

A long-term #drought reconstruction based on #oxygen #isotope tree ring data for central and eastern parts of Europe (Romania) bg.copernicus.org/articles/22/

bg.copernicus.orgA long-term drought reconstruction based on oxygen isotope tree ring data for central and eastern parts of Europe (Romania)Abstract. This study investigates the relationship between oxygen isotope ratios (δ18O) in oak tree ring cellulose and past drought variability in Letea Forest, Romania. A δ18O site chronology spanning 1803–2020 was compiled from seven individual time series. δ18O values exhibited a significant negative correlation with moisture-related variables (cloud cover, relative humidity, and precipitation) and a positive correlation with temperature and sunshine duration. This confirms that δ18O from tree rings can be a good proxy for moisture availability. The strongest correlation was found between δ18O and the August Standardized Precipitation Evapotranspiration Index for an accumulation period of 9 months (SPEI9) for central and eastern Europe. This highlights SPEI9 as a superior indicator of drought compared to individual parameters like temperature or precipitation. Using a linear regression model, we reconstructed August SPEI9 variability for the past 200 years. The reconstruction captured interannual and decadal variations, with distinct wet and dry periods. Analysis of large-scale atmospheric circulation patterns revealed a link between high δ18O values (indicating dry conditions) and a high-pressure system over the North Atlantic. Conversely, low δ18O values (indicating wet conditions) corresponded to negative pressure anomalies over Europe. Moreover, extreme values of δ18O are also associated with the prevalence of a hemispheric teleconnection pattern, namely wave number 4. This δ18O chronology and the corresponding August SPEI9 reconstruction offer valuable tools for understanding past climate variability and its relationship with large-scale atmospheric and oceanic circulation patterns.
Public
Niels de Winter

A clumped #isotope calibration of #coccoliths at well-constrained culture temperatures for marine #temperature #reconstructions

cp.copernicus.org/articles/20/

cp.copernicus.orgA clumped isotope calibration of coccoliths at well-constrained culture temperatures for marine temperature reconstructionsAbstract. Numerous recent studies have tested the clumped isotope (Δ47) thermometer on a variety of biogenic carbonates such as foraminifera and bivalves and showed that most follow a common calibration. However, there may be a difference between biogenic-carbonate-based calibrations and the most recent inorganic carbonate calibrations that are assumed to have formed close to isotopic equilibrium. Biogenic calibrations such as those based on foraminifera from seafloor sediments suffer from uncertainties in the determination of the calcification temperatures. Therefore, well-constrained laboratory cultures without temperature uncertainty can help resolve these discrepancies. Although the sample size requirements for a reliable Δ47 measurement have decreased over the years, the availability and preservation of many biogenic carbonates are still limited and/or require substantial time to be extracted from sediments in sufficient amounts. Coccoliths, on the other hand, are abundant and often well-preserved in sediments, and they are a potential interesting target for palaeoceanography. We thus determined the Δ47–temperature relationship for coccoliths due to their relative ease of growth in the laboratory. The carbon and oxygen isotopic compositions of coccolith calcite have limited use in palaeoenvironmental reconstructions due to physiological effects that cause variability in the carbon and oxygen isotopic fractionation during mineralization. However, the relatively limited data available suggest that clumped isotopes may not be significantly influenced by these effects. We cultured three species of coccolithophores under controlled carbonate system conditions with CO2(aq) concentrations between 5 and 45 µM, pH between 7.9 and 8.6 units, and temperatures between 6 and 27 °C. Our well-constrained results agree with a previous culture study that there are no apparent species- or genus-specific vital effects on the Δ47–temperature relationship in coccolithophores despite significant deviations from equilibrium in the C and O isotopic composition. We find that while varying environmental parameters other than temperature does not have a significant effect on Δ47, changing the parameters yields coccolith Δ47–temperature calibrations that agree within 1.2 ppm. Our coccolith-specific Δ47–temperature calibration with well-constrained temperatures shows a consistent, positive offset of 2–3 °C to the inorganic carbonate calibrations, which point to as yet unknown coccolith-specific disequilibrium effects. Thus, we suggest the use of our coccolith-specific calibration for further coccolith palaeoceanographic studies and that calibrations derived from laboratory-grown biogenic carbonates are desirable to reinforce the confidence of clumped-isotope-based temperature reconstructions in palaeoceanography.
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