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1. InterCarb: A Community Effort to Improve Interlaboratory Standardization of the Carbonate Clumped Isotope Thermometer Using Carbonate Standards

   https://doi.org/10.1029/2020GC009588  

   Bernasconi, S. M. ; Daëron, M. ; Bergmann, K. D. ; Bonifacie, M. ; Meckler, A. N. ; Affek, H. P. ; Anderson, N. ; Bajnai, D. ; Barkan, E. ; Beverly, E. ; et al ( May 2021 , Geochemistry, Geophysics, Geosystems)

   Increased use and improved methodology of carbonate clumped isotope thermometry has greatly enhanced our ability to interrogate a suite of Earth‐system processes. However, interlaboratory discrepancies in quantifying carbonate clumped isotope (Δ₄₇) measurements persist, and their specific sources remain unclear. To address interlaboratory differences, we first provide consensus values from the clumped isotope community for four carbonate standards relative to heated and equilibrated gases with 1,819 individual analyses from 10 laboratories. Then we analyzed the four carbonate standards along with three additional standards, spanning a broad range of δ⁴⁷and Δ₄₇values, for a total of 5,329 analyses on 25 individual mass spectrometers from 22 different laboratories. Treating three of the materials as known standards and the other four as unknowns, we find that the use of carbonate reference materials is a robust method for standardization that yields interlaboratory discrepancies entirely consistent with intralaboratory analytical uncertainties. Carbonate reference materials, along with measurement and data processing practices described herein, provide the carbonate clumped isotope community with a robust approach to achieve interlaboratory agreement as we continue to use and improve this powerful geochemical tool. We propose that carbonate clumped isotope data normalized to the carbonate reference materials described in this publication should be reported as Δ₄₇(I‐CDES) values for Intercarb‐Carbon Dioxide Equilibrium Scale.

    

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2. Paleogene Paleohydrology of Ellesmere and Axel Heiberg Islands (Arctic Canada) From Palustrine Carbonates

   https://doi.org/10.1029/2023PA004609  

   Padgett, Ashly B. ; Hyland, Ethan G. ; West, Christopher K. ; Burgener, Landon K. ; Greenwood, David R. ; Basinger, James F. ( October 2023 , Paleoceanography and Paleoclimatology)

   Ancient greenhouse periods are useful analogs for predicting effects of anthropogenic climate change on regional and global temperature and precipitation patterns. A paucity of terrestrial data from polar regions during warm episodes challenges our understanding of polar climate responses to natural/anthropogenic change and therefore our ability to predict future changes in precipitation. Ellesmere and Axel Heiberg Islands in the Canadian Arctic preserve terrestrial deposits spanning the late Paleocene to middle Eocene (59–45 Ma). Here we expand on existing regional sedimentology and paleontology through the addition of stable (δ¹³C, δ¹⁸O) and clumped (Δ₄₇) isotope analyses on palustrine carbonates. δ¹³C isotope values range from −4.6 to +12.3‰ (VPDB), and δ¹⁸O isotope values range from −23.1 to −15.2‰ (VPDB). Both carbon and oxygen isotope averages decrease with increasing diagenetic alteration. Unusually enriched carbon isotope (δ¹³C) values suggest that analyzed carbonates experienced repeated dissolution‐precipitation enrichment cycles, potentially caused by seasonal fluctuations in water availability resulting in summer carbonate dissolution followed by winter carbonate re‐precipitation. Stable isotopes suggest some degree of precipitation seasonality or reduction in winter water availability in the Canadian Arctic during the Paleogene. Clumped (Δ₄₇) temperature estimates range from 52 to 121°C and indicate low temperature solid‐state reordering of micritic samples and diagenetic recrystallization in sparry samples. Average temperatures agree with vitrinite reflectance data for Eureka Sound Group and underlying sediments, highlighting structural complexity across the region. Broadly, combined stable and clumped isotope data from carbonates in complex systems are effective for describing both paleoclimatic and post‐burial conditions.

    

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3. A window to the Early Cretaceous North American Climate and Environment: The ‘Lake Carpenter’ lacustrine strata of the Cedar Mountain Formation

   Suarez, M.B. ; Al-Suwaidi, A. ; Kirkland, J.I. ; Snell, K. ; Moller, A. ; McLean, N. ; Suarez, C.A. ; Montgomery, E. ; Paige, M. ( January 2023 , The Anatomical record Supplement)

   The Cedar Mountain Formation is thought to span a significant portion of the lower Cretaceous and the base of the upper Cretaceous (Valanginian to Cenomanian). As such, the Cedar Mountain Formation is important for understanding the transition of terrestrial ecosystems from those characterized by pre-angiosperm ecosystems of the Jurassic to the angiosperm-dominated ecosystems that characterized the height of dinosaur diversity in the later part of the Cretaceous. Lacustrine strata offer unique opportunities to shed light on environmental and climate conditions of the past. This study presents results from a multi-proxy study of lacustrine strata in the Cedar Mountain Formation termed “Lake Carpenter.” The sequence of strata is about ~30 m thick and located near Arches National Park. The lower ~7 m is characterized by dark organic-rich mudstones, shales, and tan limestones and dolostone. The middle portion between about 7 and 25m consists of more massive carbonate-rich strata with abundant aquatic fossils including ostracodes, charophytes, and fish scales. The upper portion to about 30 m consists of green to tan mudstones with carbonate nodules and increases in siliciclastic content. Carbonate mineralogies include calcite, high-magnesium calcite, and dolomite (including dolomicrites) based on XRD analyses. To put the lacustrine sequence into stratigraphic context, bulk organic C isotope values were utilized to construct a chemostratigraphic record. The carbon isotope values range from -32.3‰ to -21.1‰ vs. VPDB. Zircons from four suspected volcanic ash layers were analyzed for U-Pb using LA-ICP-MS. One of these produced concordant Cretaceous dates. The youngest zircons from this sample was analyzed using CA-ID-TIMS and produced a date of 115.65 ± 0.18 Ma. Based on the chemostratigraphic record and the U-Pb date, the deposition of the lacustrine sequence occurs in the mid to late Aptian and spans a time that is thought to have coincided with a cold snap based on marine records. Carbonate analyses of the carbonates within the lacustrine sequence ranges from -9.2‰ to +5.4‰ vs. VPDB for carbon and -9.3 to -0.3‰ vs. VPDB for oxygen. Overall, carbonate isotope data is positively covariant and along with the minerology, seems to suggest that the lake was a closed-basin, alkaline lake and would have likely experience significant evaporation. To investigate paleotemperature, selected samples were analyzed for clumped isotope values (47) to determine temperature of formation. Preliminary temperature estimates of calcite formation range from 27°C to 41°C. Estimates for dolomite range from 19°C to 21°C. Lacustrine carbonate formation typically is biased toward spring and summer and as such some of these temperatures (particularly the values for dolomites) seem slightly lower than expected for a greenhouse climate but may be consistent with a “cold-snap” during the late Aptian. Palustrine carbonates from the type section of the Ruby Ranch Member range 19.8°C to 44.5°C (Suarez et al. 2021) and suggests the lacustrine strata records a similar range in temperatures during the Aptian Stage in this part of North America. REFERENCES CITED: Suarez, MB, Knight, J, Snell, KE, Ludvigson, GA, Kirkland, JI, Murphy, L 2020. Multiproxy paleoclimate estimates of the continental Cretaceous Ruby Ranch Member of the Cedar Mountain Formation. In: Bojar, A-V, Pelc., A, Lecuyer, C, editors. Stable Isotopes Studies of Water Cycle and Terrestrial Environments. Geol Soc, London, Spec Pub, 507: https://doi.org/10.1144/SP507-2020-85 KEYWORDS: Early Cretaceous, lacustrine, stable isotopes, paleoclimate Presentation Mode: Invited Speaker 

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4. Modeling the Measurement: Δ 47 , Corrections, and Absolute Ratios for Reference Materials

   https://doi.org/10.1029/2018GC008166  

   Olack, Gerard ; Colman, Albert S. ( July 2019 , Geochemistry, Geophysics, Geosystems)

   Clumped isotope studies on CO₂, Δ₄₇, that is the excess in the isotopologue containing both¹³C and¹⁸O at mass 47, can be very useful since they can give temperature estimates independent of the bulk isotopic composition. The measurement itself can be affected by a number of items. Here we develop a data processing model to examine the effects different interferences might have on the final calculated value. It incorporates known issues, for example, pressure baseline,¹⁷O excess, and shifts in absolute ratios for primary reference materials and parameters used for¹⁷O correction. We also included linearity effects as well as differences in isotopologue absolute abundances at a givenm/z. What normally would be considered acceptable mass spectrometer⁴⁵Rand⁴⁶Rlinearity can skew Δ₄₇results. That is 0.04‰/V and −0.04‰/V linearity on⁴⁵Rand⁴⁶Rrespectively would also cause an apparent shift in the parameters used for¹⁷O corrections. Measurements were made on CO₂(g) equilibrated with water, and we were able to match up the effects seen with model results. Linearity and small differences in amplitude between sample and working reference gas affected Δ₄₇determination, as did apparent shifts in isotopologue abundances under different conditions. This may (partially) account for discrepancies seen in Δ₄₇‐temperature calibrations curves between laboratories. We also developed an easy way to precisely calculate the δ¹³C and δ¹⁸O that works well in spreadsheets without the need for multiple iterations.

    

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5. Seasonally Variable Aquifer Discharge and Cooler Climate in Bermuda During the Last Interglacial Revealed by Subannual Clumped Isotope Analysis

   https://doi.org/10.1029/2020PA004145  

   Zhang, Jade Z. ; Petersen, Sierra V. ; Winkelstern, Ian Z. ; Lohmann, Kyger C. ( May 2021 , Paleoceanography and Paleoclimatology)

   Faunal analog reconstructions suggest that Last Interglacial (MIS 5e) sea surface temperatures were cooler around Bermuda and in the Caribbean than modern climate. Here we describe new and revised clumped isotope measurements ofCittarium picafossil shells supporting previous findings of cooler than modern temperatures in Bermuda during the Last Interglacial. We resolve temperature and δ¹⁸O_wdifferences between two closely located and apparently coeval sites described in Winkelstern et al. (2017),https://doi.org/10.1002/2016pa003014through reprocessing raw isotopic data with the updated Brand/IUPAC parameters. New subannual‐resolution clumped isotope data reveal large variations in δ¹⁸O_wout of phase with seasonal temperature changes (i.e., lower δ¹⁸O_wvalues in winter). Supported by modern δ¹⁸O_wmeasurements identifying similar processes occurring today, we suggest past variations in coastal δ¹⁸O_wwere driven by seasonally variable freshwater discharge from a subterranean aquifer beneath the island. Taken together, our results emphasize the importance of δ¹⁸O_win controlling carbonate δ¹⁸O, and suggest that typical assumptions of constant δ¹⁸O_wshould be made cautiously in nearshore settings and can contribute to less accurate reconstructions of paleotemperature.

    

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