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Paleo-proxy reconstructions reveal a moistening of the American Southwest during the Last Glacial Maximum (LGM; 21 ka). However, the primary mechanisms driving the moistening trend are still debated, with relatively few studies focused on hypotheses related to synoptic changes in precipitation. Analysis of the Paleoclimate Intercomparison Model Project (PMIP3) simulations shows enhancement of precipitation in the southwest and south-central United States during the winter and summer. Here, we suggest that summertime eastward phase shifting of stationary waves at the LGM enhanced precipitation in the south-central United States and dried the southeastern United States. Mechanism denial experiments performed with version 3 of the Hadley Centre Coupled Model (HadCM3) indicate that the thermodynamic effect of the Laurentide Ice Sheet forced eastward phase shifting of stationary waves. By comparing a synthesis of LGM proxies to the PMIP3 ensemble, we find models that compare more favorably to the reconstructions simulate a weaker Laurentide ice thermodynamic effect, smaller eastward phase shifting of stationary waves, and weaker jet stream anomalies. Significance Statement Our study is motivated by the impact of climate change on hydroclimate in North America, especially in the semiarid areas near the southwestern United States, and the persistent problem of significant disagreements among CMIP model projections. Yet modern models and observations alone cannot tell us the likeliest climate change outcome in this region. Here we analyze precipitation during the LGM reconstructed from proxies and as simulated by the PMIP3, which reveal a precipitation trend with wetting in the southwestern United States and drying in the southeastern United States. Our interpretation of the PMIP3 simulations involves application of simple theories for midlatitude stationary waves, and indicates that the LGM precipitation is generated by the phase shift of stationary waves from the enhancement of jet speeds. Our model–data comparison also suggests that in the PMIP3 simulations, weak LGM jet stream anomalies, due to weak polar amplification, compare more favorably to the proxies.

Constraints on the evolution of atmospheric CO2 levels throughout Earth's history are foundational to our understanding of past variations in climate. Despite considerable effort, records vary in their temporal and spatial coverage and estimates of past CO2 levels do not always converge, and therefore new records and proxies are valuable. Here we reconstruct atmospheric CO2 values across major climate transitions over the past 16 million years using the boron isotopic composition (δ11B) of planktic foraminifera from 89 samples obtained from two sites in the West Pacific Warm Pool, Ocean Drilling Program (ODP) Sites 806 and 807, measured using high-precision multi-collector inductively coupled plasma mass spectrometry. We compare our results to published data from ODP Site 872, also in the Western Equatorial Pacific, that goes back to 22 million years ago. These sites are in a region that today is near equilibrium with the atmosphere and are thought to have been in equilibrium with the atmosphere for the interval studied. We show that δ11B data from this region are consistent with other boron-based studies. The data show evidence for elevated pCO2 during the Middle Miocene and Early to Middle Pliocene, and reductions in pCO2 of ∼200 ppm during the Middle Miocene Climate Transition, ∼250 ppm during Pliocene Glacial Intensification and ∼50 ppm during the Mid-Pleistocene Climate Transition. During the Mid-Pleistocene Transition there is a minimum pCO2 at marine isotopic stage (MIS) 30. Our results are consistent with a coupling between pCO2, temperature and ice sheet expansion from the Miocene to the late Quaternary.

Background: Editorial board members of academic journals are often considered gatekeepers of knowledge and role models for the community. Editorial boards should have sufficiently diverse backgrounds to facilitate the publication of manuscripts with a wide range of research paradigms, methods, and cultural perspectives.Objectives: This study critically evaluates changes in the representation of binary gender and geographic diversity over time for the editorial boards of Chemical Geology and Geochimica et Cosmochimica Acta. These are the two flagship geochemistry journals from the European Association of Geochemistry and the Geochemical Society, respectively.Methods: Composition of editorial boards was taken from the first issue of the year in question and editorial board members were coded for country of affiliation and binary gender. Results: Gender parity, limited to men and women, and geographic representation of the editorial boards of Chemical Geology and Geochimica et Cosmochimica Acta, have steadily increased between the late 1980’s and 2021. However, geographic distribution remains largely dominated by affiliations from North America and Western Europe. The Editor-in-Chief or board of editors have a significant impact on the level of diversity of the editorial board. With nearly every newly appointed editor, both geographic and gender diversity may evolve. However, the persisting substantial underrepresentation of editorial board members from outside of North America and Europe is of concern and needs to be the focus of active recruitment and ongoing monitoring. This approach will ensure that traditionally low levels of geographic diversity are mitigated and representation of our global communities is improved and maintained in the future. Conclusions: Improving diversity and inclusion among editorial boards as well as strengthening journal and disciplinary reputations will reinforce one another. Instituting a rotating editorship with an emphasis on embedding broader geographic networks and more equitable international recruitment could ensure sustained and improved geographic, gender, and wider representation, which, as a consequence, may lift scientific originality and the quality of published research.

Supplementary Tables, information about clumped isotope quality assurance, and code to accompany "Dual carbonate clumped isotopes (Δ47-Δ48) constrains kinetic effects and timescales in peridotite-associated springs at The Cedars, Northern California" published inGeochimica et Cosmochimica Acta.

Code to accompany Equilibrated gas and carbonate standard-derived dual (Δ47 and Δ48) clumped isotope values The R script findcutpoints.R contains the functions that should be loaded into memory ahead of data quality control. Analyses_Lucarelli_et_al.R contains script for each data cleaning step and instructions for exporting final data to spreadsheets. Inter-instrumental_comparisons_Lucarelli_et_al.R contains inter-instrumental comparisons and power analyses.

It has been proposed that the northeastern Tibetan Plateau (NETP) was the most recent plateau sub-region to gain elevation, leading to profound environmental changes in northern East Asia around the mid-Pliocene (ca. 3.6 Ma). Alternatively, environmental changes in the region have been linked to ongoing global cooling and glacial intensification after 3.3 Ma. Here, we test these hypotheses using Plio-Pleistocene estimates of paleotemperatures and paleoelevations in the NETP derived from oxygen and carbon stable isotopic composition (n = 792) and clumped isotope measurements (n = 32) of carbonates from a Lake Qinghai Basin sediment core, eastern NETP. From 5 to 2 Ma, basinal mean annual air temperatures (MAATs) decreased by 4.9 ± 2.8 °C at rates of 1.6 °C ± 0.5 °C/myr, concurrently with regional and global cooling. However, the largest MAAT decline occurs between ca. 4.8−3.7 Ma (4.1 ± 3.2 °C) and ca. 3.4−2.0 Ma (−0.3 ± 2.8 °C) and may correspond with an elevation change of 1.0 ± 1.0 km at 3.6 Ma, coincident with tectonic activity in the Lake Qinghai Basin and several other basins in the NETP and its foreland. Taken together, these results suggest a combination of global cooling and a small magnitude of surface uplift (

Upper Cretaceous-Cenozoic marine sequences preserved between 30 and 350 masl across southern South Africa record a complex history of climatic and tectonic changes. In this study, we measure the strontium (Sr) isotope composition of fossil shark teeth, echinoderms, corals and oyster shells to chronostratigraphically constrain the ages of these sequences. The method requires careful petrographic screening and micro-drilling of the samples to avoid possible alteration by diagenesis. To assess palaeoenvironmental effects in the shells we measured the Mg/Ca elemental ratios and O isotope values using electron microprobe analysis (EMPA) and secondary ion mass spectrometry (SIMS). In addition, we employed carbonate clumped isotope thermometry to test palaeotemperatures reconstruction. The analysis of recent to modern stromatolites by clumped isotopes yields an average temperature of 20.2°C, in agreement with present day observations. The fossil oyster shells suggest a warmer (23.0°C) seawater palaeotemperature, possibly due to major deglaciation and sea-level rise during the Neogene. We also find that transgressions occurred above 200 to 350 m elevation during: 1) the Campanian-Maastrichian (~75 Ma); 2) the mid-Oligocene (32 to 26 Ma); and 3) the Messinian-Zanclean (6 to 5 Ma). These three episodes are linked to well-known variations in global sea level and regional tectonic processes that could have affected the continental margin differently. The most recent transgression coincides with a maximum global sea-level rise of ~50 m at ca. 5.3 Ma, and a worldwide plate kinematic change around 6 Ma, which in Eurasia led to the closure of the Mediterranean Sea. In the Eastern Cape of South Africa, the new dates of analyzed oyster shells constrain a minimum uplift rate of ca. 150 m/Myr during this tectonic activity. The results have important implications for robust calibration of relative sea level in southern Africa.

Water, weather, and climate affect everyone. However, their impacts on various communities can be very different based on who has access to essential services and environmental knowledge. At the same time, structural discrimination, including racism and other forms of privileging and exclusion, affects people's lives and health, with ripples across all sectors of society. In the United States, the need to equitably provide weather, water, and climate services is uplifted by the Justice40 Initiative (Executive Order 14008), which mandates 40% of the benefits of certain federal climate and clean energy investments flow to disadvantaged communities. To effectively provide such services, particularly given increasing weather-related disasters, public health impacts of climate change, and disparities in terms of which population subgroups are most affected, systemic reform is required that centers equity in all undertakings. It is imperative that those with positional authority and resources manifest responsibility by: (1) recognizing, including, and prioritizing community expertise; (2) building a stronger and more equitable workforce; (3) communicating about climate risk in equitable, relevant, timely and culturally responsive ways; and (4) developing new models of relationships between communities and the academic sector.

Boron isotope systematics of planktonic foraminifera from core-top sediments and culture experiments have been studied to investigate the sensitivity of δ11B of calcite tests to seawater pH. However, our knowledge of the relationship between δ11B and pH remains incomplete for many taxa. Thus, to expand the potential scope of application of this proxy, we report δ11B data for seven different species of planktonic foraminifera from sediment core tops. We utilize a method for the measurement of small samples of foraminifera and calculate the δ11B -calcite sensitivity to pH for Globigerinoides ruber, Trilobus sacculifer (sacc or without sacc), Orbulina universa, Pulleniatina obliquiloculata, Neogloboquadrina dutertrei, Globorotalia menardii, and Globorotalia tumida, including for unstudied core tops and species. These taxa have diverse ecological preferences and are from sites that span a range of oceanographic regimes, including some that are in regions of air–sea equilibrium and others that are out of equilibrium with the atmosphere. The sensitivity of δ11B carbonate to δ11B borate (e.g., Δδ11Bcarbonate∕Δδ11Bborate ) in core tops is consistent with previous studies for T. sacculifer and G. ruber and close to unity for N. dutertrei, O. universa, and combined deep-dwelling species. Deep-dwelling species closely follow the core-top calibration for O. universa, which is attributed to respiration-driven microenvironments likely caused by light limitation and/or symbiont–host interactions. Our data support the premise that utilizing boron isotope measurements of multiple species within a sediment core can be utilized to constrain vertical profiles of pH and pCO2 at sites spanning different oceanic regimes, thereby constraining changes in vertical pH gradients and yielding insights into the past behavior of the oceanic carbon pumps.

International audience; There is increasing concern with anthropogenic greenhouse gas emissions that ocean warming, in concert with summer and winter precipitation changes, will induce anoxia in multiple ocean basins, such as in the Mediterranean Sea. Although the hydrological changes in the eastern Mediterranean are quite well constrained, quantitative evidence of changes in sea surface temperature (SST) and winter rainfall in the western Mediterranean across the past interglacials is relatively scarce. In this study, we use a combination of trace element (Ba/Ca and Mg/Ca) and stable oxygen isotope composition of planktonic foraminifera from a sediment core located off the Golo River, Corsica (northern Tyrrhenian Sea) to reconstruct variations in SSTs and sea surface salinities (SSS) during the Holocene (MIS 1) and warm periods of the past two interglacials (MIS 5, 7). We also analyse PMIP3 model simulations for the mid-Holocene to investigate the mechanism for moisture transport in the western Mediterranean. Our Mg/Ca-SSTs, Ba/Ca-salinity and derived δ18O-seawater records suggest that the warm periods of the past interglacials were characterized by high river discharge and lower SSS in the northern Tyrrhenian Sea. Since this region is ideally located on the trajectory of wintertime storm tracks across the North Atlantic into the Mediterranean Sea and is also outside the influence of the ITCZ-controlled summer monsoon rains, we suggest enhanced winter rainfall during the past interglacials. Our analysis of PMIP3 model simulations for mid-Holocene also support increased south-westerly moisture transport into the western Mediterranean originating from the North Atlantic. We also find evidence that long-term amplitude of the salinity decrease tightly follows eccentricity. We suggest that these hydrologic changes in the western Mediterranean, and the northern Mediterranean borderlands as a whole, were a contributing factor, together with local cyclogenesis and African summer monsoon rainfall, to basin-wide anoxia in the past. Our findings offer new constraints to the amplitude and cause of winter rainfall changes in the Mediterranean during past warm periods.

During the Last Glacial Maximum (LGM) and subsequent deglaciation, the Great Basin in the southwestern United States was covered by numerous extensive closed-basin lakes, in stark contrast with the predominately arid climate observed today. This transition from lakes in the Late Pleistocene to modern aridity implies large changes in the regional water balance. Whether these changes were driven by increased precipitation rates due to changes in atmospheric dynamics, decreased evaporation rates resulting from temperature depression and summer insolation changes, or some combination of the two remains uncertain. The factors contributing to these large-scale changes in hydroclimate are critical to resolve, given that this region is poised to undergo future anthropogenic-forced climate changes with large uncertainties in model simulations for the 21st century. Furthermore, there are ambiguous constraints on the magnitude and even the sign of changes in key hydroclimate variables between the Last Glacial Maximum and the present day in both proxy reconstructions and climate model analyses of the region. Here we report thermodynamically derived estimates of changes in temperature, precipitation, and evaporation rates, as well as the isotopic composition of lake water, using clumped isotope data from an ancient lake in the northwestern Great Basin, Lake Surprise (California). Compared to modern climate, mean annual air temperature at Lake Surprise was 4.7 °C lower during the Last Glacial Maximum, with decreased evaporation rates and similar precipitation rates to modern. During the mid-deglacial period, the growth of Lake Surprise implied that the lake hydrologic budget briefly departed from steady state. Our reconstructions indicate that this growth took place rapidly, while the subsequent lake regression took place over several thousand years. Using models for precipitation and evaporation constrained from clumped isotope results, we determine that the disappearance of Lake Surprise coincided with a moderate increase in lake temperature, along with increasing evaporation rates outpacing increasing precipitation rates. Concomitant analysis of proxy data and climate model simulations for the Last Glacial Maximum are used to provide a robust means to understand past climate change, and by extension, predict how current hydroclimates may respond to expected future climate forcings. We suggest that an expansion of this analysis to more basins across a larger spatial scale could provide valuable insight into proposed climate forcings, and aid in climate model process depiction. Ultimately, our analysis highlights the importance of temperature-driven evaporation as a mechanism for lake growth and retreat in this region.

The high-precision analysis of the abundance of the dominant m/z 47 CO2 isotopologue derived from acid digestion of carbonate minerals (13C18O16O; denoted by Δ47) forms the basis for carbonate clumped isotope thermometry. Since the first measurements were published 16 years ago, considerable effort has gone into characterizing the relationship between Δ47 and carbonate precipitation temperature, and in identifying carbonates that do not achieve isotopic equilibrium. Mass spectrometry is now capable of the paired measurement of the primary m/z 47 and m/z 48-isotopologues (Δ47 and Δ48; 12C18O2 is denoted by Δ48), which has the potential to place additional constraints on kinetic isotope effects in carbonate minerals and trace distinct reaction pathways. Here, we explored factors that contribute to calcite mineral equilibrium and disequilibrium in Δ47 and Δ48 using a combination of experiments and theoretical calculations with three types of models. We precipitated calcite at pH 8.3 with carbonic anhydrase (CA) to approach quasi-isotopic equilibrium in the dissolved inorganic carbon pool and report values for Δ47, Δ48, and oxygen isotopes (δ18O) for calcite grown over a temperature range from 5 to 25 oC and compare our findings to predictions from an ion-by-ion model that support equilibrium precipitation. We also compare results to the Devils Hole slow-growing cave calcite, and other published temperature calibration data. We report the following combined equilibrium calibration relationships: Δ48 CDES 90 = (0.429 ± 0.010) Δ47 CDES 90 - (0.006 ± 0.006); r2 = 0.98; Δ47 I-CDES = (0.037 ± 0.001) × 106T-2 + (0.178 ± 0.009); r2 = 0.99; Δ48 CDES 90 = (0.015 ± 0.0005) × 106T-2 + (0.078 ± 0.006); r2 = 0.98. We used paired measurements of Δ47 and Δ48 to constrain kinetic isotope effects in calcite precipitated at pH ranging from 8.3-11 and temperatures from 5 to 25 oC, with and without CA present, and observe kinetic enrichments in Δ47, negative (hyperstochastic) values for Δ48, and depleted values of δ18O, compared to equilibrium values. Experimentally constrained kinetic trajectories, when compared with an ion-by-ion model and IsoDIC theoretical predictions, are consistent with CO2 hydration/hydroxylation. Mixing drives elevated Δ47 and Δ48 values and was assessed using mixing experiments with endmembers of varying isotopic compositions and compared to a Δ47 and Δ48 mixing model that constrains nonlinear mixing trajectories for calcite. While mixing may induce artifacts in two-component mixtures when endmember bulk compositions differ by more than 7 ‰, or if endmember Δ47 and Δ48 differ by more than 0.03 ‰, this should be detectable and potentially correctible using paired clumped isotope measurements and is unlikely to be important for some materials.

Carbonate clumped isotope thermometry (Δ47) is a temperature proxy that is becoming more widely used in the geosciences. Most calibration studies have used ordinary least squares linear regressions...

Picking foraminifera from sediment samples is an essential, but repetitive and low-reward task that is well-suited for automation. The first step toward building a picking robot is the development of an automated identification system. We use machine learning techniques to train convolutional neural networks (CNNs) to identify six species of extant planktic foraminifera that are widely used by paleoceanographers, and to distinguish the six species from other taxa. We employ CNNs that were previously built and trained for image classification. Foraminiferal training and identification use reflected light microscope digital images taken at 16 different illumination angles using a light-emitting diode (LED) ring. Overall machine accuracy, as a combination of precision and recall, is better than 80% even with limited training. We compare machine performance to that of human pickers (six experts and five novices) by tasking each with the identification of 540 specimens based on images. Experts achieved comparable precision but poorer recall relative to the machine, with an average accuracy of 63%. Novices scored lower than experts on both precision and recall, for an overall accuracy of 53%. The machine achieved fairly uniform performance across the six species, while participants' scores were strongly species-dependent, commensurate with their past experience and expertise. The machine was also less sensitive to specimen orientation (umbilical versus spiral views) than the humans. These results demonstrate that our approach can provide a versatile ‘brain’ for an eventual automated robotic picking system.

Rationale: Clumped isotope geochemistry examines the pairing or clumping of heavy isotopes in molecules and provides information about the thermodynamic and kinetic controls on their formation. The first clumped isotope measurements of carbonate minerals were first published 15 years ago, and since then, interlaboratory offsets have been observed, and laboratory and community practices for measurement, data analysis, and instrumentation have evolved. Here we briefly review historical and recent developments for measurements, share Tripati Lab practices for four different instrument configurations, test a recently published proposal for carbonate-based standardization on multiple instruments using multi-year data sets, and report values for 21 different carbonate standards that allow for recalculations of previously published data sets. Methods: We examine data from 4628 standard measurements on Thermo MAT 253 and Nu Perspective IS mass spectrometers, using a common acid bath (90°C) and small-sample (70°C) individual reaction vessels. Each configuration was investigated by treating some standards as anchors (working standards) and the remainder as unknowns (consistency standards). Results: We show that different acid digestion systems and mass spectrometer models yield indistinguishable results when instrument drift is well characterized. For linearity correction, mixed gas-and-carbonate standardization or carbonate-only standardization yields similar results. No difference is observed in the use of three or eight working standards for the construction of transfer functions. Conclusions: We show that all configurations yield similar results if instrument drift is robustly characterized and validate a recent proposal for carbonate-based standardization using large multiyear data sets. Δ values are reported for 21 carbonate standards on both the absolute reference frame (ARF; also refered to as the Carbon Dioxide Equilibrated Scale or CDES) and the new InterCarb-Carbon Dioxide Equilibrium Scale (I-CDES) reference frame, facilitating intercomparison of data from a diversity of labs and instrument configurations and restandardization of a broad range of sample sets between 2006, when the first carbonate measurements were published, and the present.

Carbonate clumped isotope thermometry has been applied to fossil mollusk shells from Tibet to reconstruct the paleoclimate and paleoelevation of the region. However, inferred paleoelevation and climatic conditions from this proxy are inconsistent with paleontological evidence. Here, we report new clumped isotope data from both modern and fossil (5–4 Ma) freshwater mollusk shells with the results of X-ray diffraction (XRD) analyses of fossil shells from the Himalayan-Tibetan Plateau. Although all of the fossil shells analyzed in this study appeared pristine based on visual inspection, XRD data reveal that more than half of these apparently “pristine” fossil shells contain trace amounts of calcite. Clumped isotope temperatures derived from the fossil shells display a large range of variation (>22 °C). Among the fossil shells analyzed, those containing traces of calcite have yielded temperatures that are on average ∼10 °C lower than those with no detectable calcite from the same strata. These observations suggest that clumped isotope alteration can occur in aragonite shells in low-temperature environments and even in shells with no visible signs of alteration that contain only traces of calcite. The temperatures derived from fossil shells with no detectable calcite are on average 4 °C higher than those derived from modern shells, indicating that southwest Tibet was warmer 4–5 Ma than today. After accounting for temperature change due to global cooling, the difference in clumped isotope temperatures between pristine fossil shells and modern shells suggests that the paleoelevation of the southwestern Tibetan Plateau in the Pliocene was similar to its present-day elevation.

International audience

With the development of the carbonate clumped isotope () geothermometer, many –temperature calibrations based on biogenic and abiogenic carbonates have been generated in recent years. However, there is still not a robust empirical calibration relationship derived from lacustrine authigenic carbonates that can be used to calculate lake water temperatures from values. In this study, we present a new calibration dataset that is comprised of measurements of the clumped isotope composition of 33 lacustrine authigenic carbonates collected from terminal lakes primarily in Western China that cover a substantial altitudinal gradient, and 5 samples from other regions. These data allow us to directly derive a temperature calibration for lacustrine authigenic carbonates. Our results show a robust correlation between modern lacustrine authigenic carbonate clumped isotope composition (Δ47carb) values and independently measured mean summer water surface temperatures (Twater) (ranging from 9.8 to 26.0 °C), which confirms the utility of mass-47 clumped isotope measurements of lacustrine authigenic carbonates as a lake water temperature indicator and allows for the derivation of the following calibration equation: Δ47carb (‰) = 0.0521 ± 0.0071 × 106/ (K) + 0.0904 ± 0.0870 (R2 = 0.6224, P < 0.0001, n = 33). We observe that Δ47carb is significantly correlated to lake elevation at 35°N from 270 to 5,156 m a.s.l. The change in –derived water temperature differences through elevation gradients (i.e. lapse rate) is around 3.2 °C/km. We do not observe a significant correlation between Δ47carb and carbonate oxygen isotopic composition or independently measured lake surface water oxygen isotopic composition. Additionally, in our dataset, we find that water chemistry, carbonate precipitation rate, carbonate content and mineral-specific differences do not significantly affect Δ47carb values. Hence, the mass-47 clumped isotope signal of lacustrine authigenic carbonate can be used in paleotemperature and paleoaltimetry studies if post-depositional diagenesis did not modify the isotopic composition.

Constraints on the evolution of atmospheric CO2 levels throughout Earth's history are foundational to our understanding of past variations in climate. Despite considerable effort, estimates of past CO2 levels do not always converge and therefore new records and proxies are valuable. Here we reconstruct atmospheric CO2 values across major climate transitions over the past 17 million years using the boron isotopic composition (δ11B) of planktic foraminifera from 89 samples obtained from two sites in the West Pacific Warm Pool, Ocean Drilling Program (ODP) Sites 806 and 807. These sites are in a region that today is in equilibrium with the atmosphere and are thought to have been in equilibrium with the atmosphere for the interval studied. We use high-precision multi-collector inductively-coupled plasma mass spectrometry and show that data from these sites can reproduce the ice core record. Estimates of early Miocene pCO2 are generally higher than published reconstructions from other sites, while values for the Pliocene and Pleistocene are more similar to other datasets. We find evidence for reductions in pCO2 of ~280 µatm during the Middle Miocene Climate Transition, ~270 µatm during Pliocene Glacial Intensification, and ~50 µatm during the Mid-Pleistocene Climate Transition. There is possible evidence for a larger reduction in glacial pCO2 during the Mid-Pleistocene Transition compared to interglacial pCO2, and a minimum in pCO2 during glacial MIS 30. Our results are consistent with a coupling between pCO2, temperature and ice sheet expansion throughout the past 17 million years.

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 δ47 and Δ47 values, 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., Key Points The exclusive use of carbonate reference materials is a robust method for the standardization of clumped isotope measurementsMeasurements using different acid temperatures, designs of preparation lines, and mass spectrometers are statistically indistinguishableWe propose new consensus values for a set of seven carbonate reference materials and updated guidelines to report clumped isotope measurements