The late Paleocene and early Eocene (LPEE) are characterized by long-term (million years, Myr) global warming and by transient, abrupt (kiloyears, kyr) warming events, termed hyperthermals. Although both have been attributed to greenhouse (CO2) forcing, the longer-term trend in climate was likely influenced by additional forcing factors (i.e., tectonics) and the extent to which warming was driven by atmospheric CO2remains unclear. Here, we use a suite of new and existing observations from planktic foraminifera collected at Pacific Ocean Drilling Program Sites 1209 and 1210 and inversion of a multiproxy Bayesian hierarchical model to quantify sea surface temperature (SST) and atmospheric CO2over a 6-Myr interval. Our reconstructions span the initiation of long-term LPEE warming (~58 Ma), and the two largest Paleogene hyperthermals, the Paleocene–Eocene Thermal Maximum (PETM, ~56 Ma) and Eocene Thermal Maximum 2 (ETM-2, ~54 Ma). Our results show strong coupling between CO2and temperature over the long- (LPEE) and short-term (PETM and ETM-2) but differing Pacific climate sensitivities over the two timescales. Combined CO2and carbon isotope trends imply the carbon source driving CO2increase was likely methanogenic, organic, or mixed for the PETM and organic for ETM-2, whereas a source with higher δ13C values (e.g., volcanic degassing) is associated with the long-term LPEE. Reconstructed emissions for the PETM (5,800 Gt C) and ETM-2 (3,800 Gt C) are comparable in mass to future emission scenarios, reinforcing the value of these events as analogs of anthropogenic change.
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Free, publicly-accessible full text available September 3, 2025
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Abstract Stable isotope ratios of H (
δ 2H ), O (δ 18O), and C (δ 13C) are linked to key biogeochemical processes of the water and carbon cycles; however, the degree to which isotope-associated processes are reflected in macroscale ecosystem flux observations remains unquantified. Here through formal information assessment, new measurements ofδ 13C of net ecosystem exchange (NEE ) as well asδ 2H andδ 18O of latent heat (LH ) fluxes across the United States National Ecological Observation Network (NEON) are used to determine conditions under which isotope measurements are informative of environmental exchanges. We find all three isotopic datasets individually contain comparable amounts of information aboutNEE andLH fluxes as wind speed observations. Such information from isotope measurements, however, is largely unique. Generally,δ 13C provides more information aboutLH as aridity increases or mean annual precipitation decreases.δ 2H provides more information aboutLH as temperatures or mean annual precipitation decreases, and also provides more information aboutNEE as temperatures decrease. Overall, we show that the stable isotope datasets collected by NEON contribute non-trivial amounts of new information about bulk environmental fluxes useful for interpreting biogeochemical and ecohydrological processes at landscape scales. However, the utility of this new information varies with environmental conditions at continental scales. This study provides an approach for quantifying the value adding non-traditional sensing approaches to environmental monitoring sites and the patterns identified here are expected to aid in modeling and data interpretation efforts focused on constraining carbon and water cycles’ mechanisms. -
Marzaioli, Fabio (Ed.)Unidentified human remains have historically been investigated nationally by law enforcement authorities. However, this approach is outdated in a globalized world with rapid transportation means, where humans easily move long distances across borders. Cross-border cooperation in solving cold-cases is rare due to political, administrative or technical challenges. It is fundamental to develop new tools to provide rapid and cost-effective leads for international cooperation. In this work, we demonstrate that isotopic measurements are effective screening tools to help identify cold-cases with potential international ramifications. We first complete existing databases of hydrogen and sulfur isotopes in human hair from residents across North America by compiling or analyzing hair from Canada, the United States (US) and Mexico. Using these databases, we develop maps predicting isotope variations in human hair across North America. We demonstrate that both δ 2 H and δ 34 S values of human hair are highly predictable and display strong spatial patterns. Multi-isotope analysis combined with dual δ 2 H and δ 34 S geographic probability maps provide evidence for international travel in two case studies. In the first, we demonstrate that multi-isotope analysis in bulk hair of deceased border crossers found in the US, close to the Mexico-US border, help trace their last place of residence or travel back to specific regions of Mexico. These findings were validated by the subsequent identification of these individuals through the Pima County Office of the Medical Examiner in Tucson, Arizona. In the second case study, we demonstrate that sequential multi-isotope analysis along the hair strands of an unidentified individual found in Canada provides detailed insights into the international mobility of this individual during the last year of life. In both cases, isotope data provide strong leads towards international travel.more » « less
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Abstract. Plant wax n-alkane chain length distribution and isotopeshave been studied in modern ecosystems as proxies to reconstruct vegetationand climate of the past. However, most paleo-proxies focus on eitherconcentrations or isotopes, whereas both carry complementary information onthe mixing sources. We propose a multi-source mixing model in a Bayesianframework that evaluates both chain length distributions and isotopessimultaneously. The model consists of priors that include user-definedsource groups and their associated parametric distributions of n-alkaneconcentration and δ13C. The mixing process involves newlydefined mixing fractions such as fractional leaf mass contribution (FLMC)that can be used in vegetation reconstruction. Markov Chain Monte Carlo isused to generate samples from the posterior distribution of these parametersconditioned on both data types. We present three case studies from distinctsettings. The first involves n-C27, n-C29, and n-C31 alkanes in lake surface sediments of Lake Qinghai, China. The model provides more specific interpretations on the n-alkane input from aquatic sources than the conventional Paq proxy. The second involves n-C29, n-C31, and n-C33 alkanes in lake surface sediments in Cameroon, western Africa. Themodel produces mixing fractions of forest C3, savanna C3, andC4 plants, offering additional information on the dominant biomescompared to the traditional two-end-member mixing regime. The third couplesthe vegetation source model to a hydrogen isotope model component, usingbiome-specific apparent fractionation factors (εa) toestimate the δ2H of mean annual precipitation. By leveraging chain length distribution, δ13C, and δ2H data offour n-alkane chains, the model produces estimated precipitation δ2H with relatively small uncertainty limits. The new framework shows promise for interpretation of paleo-data but could be further improved by including processes associated with n-alkane turnover in plants, transport,and integration into sedimentary archives. Future studies on modern plantsand catchment systems will be critical to develop calibration datasets thatadvance the strength and utility of the framework.more » « less
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Paleo-CO2 reconstructions are integral to understanding the evolution of Earth system processes and their interactions given that atmospheric-CO2 concentrations are intrinsically linked to planetary function. In this talk, we use several case studies, spanning the 3 Phanerozoic Eras, to illustrate the potential of paleo-CO2 records to constrain the magnitude and state-dependency of equilibrium climate sensitivity, to advance our understanding of global biogeochemical cycles, to test the sensitivity of Earth System modeled atmospheric and oceanic circulation to PCO2 over a range of climate states, and to interrogate ecosystem—CO2—climate linkages and physiological responses to CO2. Further advances in these areas, however, are dependent on how well we ‘know’ paleo-CO2 estimates. CO2 estimates exist for much of the past half-billion years, but the degree to which the accuracy and precision of these estimates are constrained is quite variable, leading to substantial uncertainty and inconsistency in paleo-CO2 estimates. Potential sources of this uncertainty and inconsistency include an incomplete understanding of how environmental and ecophysiological conditions and processes imprint the CO2 proxy signals we measure, of the sensitivity of the CO2 estimates to this uncertainty, and differences in approaches to assigning uncertainties to CO2 estimates, among other factors. Application of newly established screening criteria, defined as part of an effort to improve our understanding of how atmospheric CO2 has varied through the Cenozoic, illustrates how the majority of pre-Cenozoic estimates are unreliable in their current form. To address these issues and to advance paleo-CO2 reconstruction, we introduce CO2PIP, a new community-scale project that takes a two-step approach to building the next generation Phanerozoic-CO2 record. Collective efforts are modernizing existing terrestrial-based CO2 estimates through additional analyses, measurements and proxy system modeling to constrain critical parameters used to estimate paleo-CO2. A set of forward proxy system models being developed in collaboration with the CO2 community, will provide a quantified representation of proxy sensitivities to environmental and ecophysiological conditions and processes that govern the CO2 signals. Ultimately, statistical inversion analysis of the simulated and modernized proxy datasets will be used to revise individual CO2 records and to build a new integrated model-data-constrained CO2 record for the Phanerozoic.more » « less
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Abstract The National Ecological Observatory Network (NEON) provides open-access measurements of stable isotope ratios in atmospheric water vapor (δ2H, δ18O) and carbon dioxide (δ13C) at different tower heights, as well as aggregated biweekly precipitation samples (δ2H, δ18O) across the United States. These measurements were used to create the NEON Daily Isotopic Composition of Environmental Exchanges (NEON-DICEE) dataset estimating precipitation (P; δ2H, δ18O), evapotranspiration (ET; δ2H, δ18O), and net ecosystem exchange (NEE; δ13C) isotope ratios. Statistically downscaled precipitation datasets were generated to be consistent with the estimated covariance between isotope ratios and precipitation amounts at daily time scales. Isotope ratios in ET and NEE fluxes were estimated using a mixing-model approach with calibrated NEON tower measurements. NEON-DICEE is publicly available on HydroShare and can be reproduced or modified to fit user specific applications or include additional NEON data records as they become available. The NEON-DICEE dataset can facilitate understanding of terrestrial ecosystem processes through their incorporation into environmental investigations that require daily δ2H, δ18O, and δ13C flux data.
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null (Ed.)Abstract Sampling intervals of precipitation geochemistry measurements are often coarser than those required by fine-scale hydrometeorological models. This study presents a statistical method to temporally downscale geochemical tracer signals in precipitation so that they can be used in high-resolution, tracer-enabled applications. In this method, we separated the deterministic component of the time series and the remaining daily stochastic component, which was approximated by a conditional multivariate Gaussian distribution. Specifically, statistics of the stochastic component could be explained from coarser data using a newly identified power-law decay function, which relates data aggregation intervals to changes in tracer concentration variance and correlations with precipitation amounts. These statistics were used within a copula framework to generate synthetic tracer values from the deterministic and stochastic time series components based on daily precipitation amounts. The method was evaluated at 27 sites located worldwide using daily precipitation isotope ratios, which were aggregated in time to provide low resolution testing datasets with known daily values. At each site, the downscaling method was applied on weekly, biweekly and monthly aggregated series to yield an ensemble of daily tracer realizations. Daily tracer concentrations downscaled from a biweekly series had average (+/- standard deviation) absolute errors of 1.69‰ (1.61‰) for δ 2 H and 0.23‰ (0.24‰) for δ 18 O relative to observations. The results suggest coarsely sampled precipitation tracers can be accurately downscaled to daily values. This method may be extended to other geochemical tracers in order to generate downscaled datasets needed to drive complex, fine-scale models of hydrometeorological processes.more » « less
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Rationale Many insect species undertake multigenerational migrations in the Afro‐tropical and Palearctic ranges, and understanding their migratory connectivity remains challenging due to their small size, short life span and large population sizes. Hydrogen isotopes (
δ 2H) can be used to reconstruct the movement of dispersing or migrating insects, but applyingδ 2H for provenance requires a robust isotope baseline map (i.e. isoscape) for the Afro‐Palearctic.Methods We analyzed the
δ 2H in the wings (δ 2Hwing) of 142 resident butterflies from 56 sites across the Afro‐Palearctic. Theδ 2Hwingvalues were compared to the predicted local growing‐season precipitationδ 2H values (δ 2HGSP) using a linear regression model to develop an insect wingδ 2H isoscape. We used multivariate linear mixed models and high‐resolution and time‐specific remote sensing climate and environmental data to explore the controls of the residualδ 2Hwingvariability.Results A strong linear relationship was found between
δ 2Hwingandδ 2HGSPvalues (r 2 = 0.53). The resulting isoscape showed strong patterns across the Palearctic but limited variation and high uncertainty for the Afro‐tropics. Positive residuals of this relationship were correlated with dry conditions for the month preceding sampling whereas negative residuals were correlated with more wet days for the month preceding sampling. High intra‐siteδ 2Hwingvariance was associated with lower relative humidity for the month preceding sampling and higher elevation.Conclusion The
δ 2Hwingisoscape is applicable for tracing herbivorous lepidopteran insects that migrate across the Afro‐Palearctic range but has limited geolocation potential in the Afro‐tropics. The spatial analysis of uncertainty using high‐resolution climatic data demonstrated that many African regions with highly variable evaporation rates and relative humidity haveδ 2Hwingvalues that are less related toδ 2HGSPvalues. Increasing geolocation precision will require new modeling approaches using more time‐specific environmental data and/or independent geolocation tools.