Isotopologue Network for Early Career Researchers (ECR)
Connect with the speakers from current and previous seminars
Amzad Hussain Laskar
Physical Research Laboratory, Ahmedabad
Reconstruction of past tropospheric oxidants and temperature variation using clumped isotopes in ice core air O2
The reconstruction of past tropospheric oxidants, such as ozone (O3), is possible using clumped isotope (specifically the abundance of 18O18O denoted by ∆36) analysis in molecular O2 trapped in ice core air. We measured ∆36 values in atmospheric O2 extracted from a Greenland ice core, covering the Holocene and the late glacial period, to uncover new insights into past variations of temperature and oxidant levels. While the Holocene is often regarded as climatically stable, discrepancies between temperature proxies and climate model results challenge this assumption. Additionally, the trend of the greenhouse gas methane is poorly understood. Atmospheric oxidants control the atmospheric methane abundance, but variations of oxidants in the past are not known since they are not preserved in paleo-climate archives. Our findings reveal that in the glacial period ∆36 was 0.07 ‰ higher than in the Late Holocene, consistent with the lower temperatures and reduced tropospheric O3 burden. Notably, ∆36 shows pronounced millennial-scale variations over the Holocene, with mid-Holocene ∆36 values being 0.06 ‰ lower than in the Late Holocene, and 0.03 ‰ below present-day conditions. Our analyses with an atmospheric chemistry-climate model and a box model suggest that the low ∆36 values in the mid-Holocene can be explained by a combination of high oxidant levels and high upper tropospheric temperatures, potentially augmented by changes in stratosphere troposphere transport. The millennial scale variability of ∆36 matches the temporal evolution of CH4, which suggests that the mid-Holocene minimum in CH4 is largely driven by tropospheric oxidants. Our ∆36 data suggest that key atmospheric features, notably oxidant levels and temperature, have varied significantly during the Holocene.
Tyler Huth
Washington University in St. Louis
Constraining lake evaporation and associated kinetic isotope fractionation via water vapor and vapor isotope mass balance
Recycled moisture from lakes and the land surface is an important component of the terrestrial water budget but is difficult to measure. Existing measurement methods include water-energy balance modeling, eddy covariance, and vapor isotope mass balance (wherein downwind vapor = upwind vapor + evapotranspiration). In examining lake evaporation, the isotope mass balance approach has traditionally relied on a system of equations with hydrogen isotopes (δD), oxygen isotopes (δ18O), and the derived d‑excess parameter (d‑excess = δD – 8×δ18O). However, the system is generally underconstrained and results can be significantly hampered by imprecise knowledge of critical parameters. We developed a method to estimate three important parameters: the fraction of recycled moisture (F), evaporation rate (E), and the magnitude of kinetic isotope fractionation during evaporation (n, the diffusion-turbulence factor). The model’s Monte Carlo simulations leveraged daily precipitation isotope data (δ18O d‑excess, and the emerging triple oxygen isotope parameter, Δʹ17O), lake water isotope data, and weather data. We tested this approach in the Lake Michigan (USA) region, a locus of previous work. The model identified 24 of 94 precipitation events as clearly influenced by lake evaporation (minimum F > 0.1). These events primarily occurred in the cold season, in agreement with prior work, and could be substantial (up to ≈60 % of total vapor). Estimated evaporation rates ranged between 0–10 mm/day and largely overlapped with independent estimates from a hydrodynamical modeling approach. In terms of kinetic fractionation, most events required lower values for the diffusion-turbulence factor (0.05 ≤ n ≤ 0.5), in agreement with values used for open ocean conditions but in contrast to values of ≥0.5 commonly applied in lake studies. Parameter n also likely varied through time due to variability in environmental conditions like the lake-air temperature gradient. We conclude this isotope-based method is valuable in providing a new perspective on moisture recycling and fulfilling previously unmet needs to estimate evaporation rate and robustly assess error. Investigations of modern lake evaporation via stable isotopes will benefit from the use of vapor isotope data, modeling seasonal or shorter timescales, and incorporating lower, variable values for the diffusion-turbulence factor.
Laetitia Guibourdenche
University of California, Los Angeles
Distinguishing methane's genetic origin
A Bayesian approach using clumped methane isotopes
Methane is an important component of Earth biogeochemical cycle and is found in the atmospheres of extraterrestrial bodies like Mars, Enceladus, and Titan. It can be produced by either microbial activity or non-microbial processes (thermogenesis or mineral-rock interactions). Therefore, it is crucial to develop tools that can identify methane genetic pathway to assess its potential biogenicity on other planets.
In addition to the classic ‘bulk’ isotopic composition of methane (ẟ13C and ẟD) and molecular ratios of alkanes (C1/C2+C3), advances in mass spectrometric measurements have allowed the development of clumped isotopes of methane (Δ13CH3D and Δ12CH2D2) as a new proxy for untangling complex sources of methane.
While thermogenic methane generally has Δ13CH3D and Δ12CH2D2 values close to temperature-dependent thermodynamic equilibrium, microbiogenic methane clumped isotope typically deviate from equilibrium. However, these general rules do not exclude false positive and false negative biosignature.
On one hand, near equilibrium methane clumped isotopic signatures can be produced by microbial activity under conditions favoring reversible intracellular reactions. On the other hand, non-microbial processes can yield Δ12CH2D2 significantly lower than thermodynamic equilibrium and potentially lead to false positive biosignatures. This complicates the distinction between microbiogenic and non-biogenic methane in the clumped isotope space.
To address this conundrum, we compiled data from the literature, for which the genetic origin of methane has been determined independently from clumped isotopes measurements. We used a Bayesian probabilistic approach to rigorously define a posterior probability map for microbial, thermogenic and abiotic fields in the clumped isotope space. This approach allows to provide a first order interpretation for the genetic methane and prompt a quantitative discussion on the potential of clumped isotope measurement as a genuine proxy for biosignature assessment.
Sara Defratyka
University of Edinburgh / National Physical Laboratory
Development of automated preconcentrator to measure clumped isotopologues of methane (Δ13CH3D and Δ12CH2D2) from the atmosphere and sources
The multiply substituted (clumped) isotopes can be used as additional tracers (aside bulk isotopic signatures, δ13C-CH4 and δD-CH4) to better distinguish methane sources, and potentially, better understand methane sinks. Measurement of methane clumped isotopes, Δ13CH3D and Δ12CH2D2 is more challenging than measurements of bulk isotopes and requires more advanced instruments. Currently, a NERC project called POLYGRAM aims to develop the sample preparation and measurement infrastructure to measure atmospheric air samples using High Resolution - Isotope Ratio Mass Spectrometer (HR-IRMS), to determine clumped isotopes collected at the world-recognised global monitoring sites at Cape Point, South Africa and station Zeppelin, Svalbard. Moreover, the project also aims to determine the clumped isotopes ratios of methane sources, like wetlands, agriculture or coal mines, as currently clumped isotopes database is constrained. In this set-up, use of custom-built preconcentrator is a key step in the measurement chain, as HR-IRMS requires ultra-pure methane samples to measure clump isotopes. During the talk, I will focus on technical and scientifical challenges and made progress in developing CH4preconcentrator.
David Zakharov
Western Michigan University
Triple O-isotope geochemistry of hydrothermal alteration and its applications to reconstructions of Earth’s near-surface conditions
Almost every rock found at the surface is altered or modified due to the reaction with liquid water abundantly present on Earth. This modification is driven by the reactivity of the Earth’s rocky shell in near-surface conditions. Modified (or altered) rocks contain information about former climates even in the deep-past (i.e., Archean) when traditional marine sedimentary proxies are challenged due to their proneness to resetting. The water-rock reactions can be traced through geological time using the isotope exchange between silicates [SiO4-—based structures] and H2O, where isotopes of O have masses 16, 17 and 18 Dalton. In this quest, my colleagues and I use O-isotopes as tracers of this fluid reactivity in shallow continental and oceanic crust. Using triple O-isotope geochemistry (δ′18O and Δ′17O) and in-situ isotope methods, we have looked at some of the oldest examples of Yellowstone-type systems, where the heat of magma and surface waters produced distinct low-δ¹⁸O altered rocks. In absence of better proxies, such materials represent a chemically resilient isotope fingerprint of ancient atmospheric precipitation that is in turn reflective of climate in distant geological past. In addition, high-precision U-Pb zircon ages are derived from such rocks pin-point the timing of the proxy. I will also present some of our recent work on submarine samples such as exchanged vent fluids, altered sedimentary rocks, and altered basalts that shed a new light on reactivity of seawater within the seafloor that creates a distinct archive of its isotope composition. Using tectonic and triple O-isotope context, I show that not every sample can be used to reflect Earth’s surface conditions in a straightforward manner. Instead, a new set of questions can be designed to study crustal conditions with materials that are altered in the near-surface environment.
Malavika Sivan
Utrecht University
Clumped isotopologue measurements as a tool to understand the sources and sinks of atmospheric methane.
I, Malavika Sivan, am a final-year PhD candidate at Utrecht University. I originally hail from Kerala, India. In 2019, I completed the BS-MS Dual Degree program at the Indian Institute of Science Education and Research Bhopal, with a major in chemistry and a minor in earth and environmental sciences. Following this, I moved to the Netherlands in 2020 to pursue my PhD in Atmospheric Physics and Chemistry at the Institute for Marine and Atmospheric Research Utrecht. Under the supervision of Dr. Elena Popa and Prof. Thomas Röckmann, my research broadly focuses on characterising geological, biological, and atmospheric methane using clumped isotopologues. Employing this novel technique, we have developed a method and measured samples across these realms to contribute a better understanding of the global methane budget.
Yangrui Guo
Guangzhou Institute of Geochemistry (GIG), Chinese Academy of Sciences
Experimental observations on clumped isotope fractionation during carbon dioxide absorption
The isotope effects observed during CO2 absorption in aqueous solutions are essential for understanding various geochemical, physicochemical, and biological processes. In this seminar, I will present our latest results from experiments that examined clumped isotope fractionation between gaseous CO2 and dissolved carbonate ions. The experiments utilized the BaCO3 precipitation approach to quickly capture newly formed inorganic carbon that is dissolved during CO2 absorption in solutions with consistent pH values. This study may provide insights into the isotope fractionation mechanism of carbon, oxygen, and clumped isotopes during CO2 hydration and hydroxylation reactions. Furthermore, the results may help to explain the commonly observed isotope disequilibrium in natural carbonates.
Tobias Agterhuis
Utrecht University
An early Cenozoic record of Atlantic deep ocean temperatures from clumped isotope thermometry
In my talk, I will present some exciting new early Cenozoic deep ocean temperature reconstructions from clumped isotope thermometry, as part of what will be chapter 2 of my PhD thesis. The deep ocean acts as a large and stable heat reservoir, and as such, the deep ocean is considered to reflect the global climate conditions on Earth. The late Paleocene and early Eocene experienced the warmest climates of the Cenozoic, with highly elevated CO2 levels and the absence of continental ice sheets on both poles. Traditionally, benthic foraminiferal oxygen isotope (δ18O) records have mostly been used to reconstruct deep-sea temperatures. However, interpretations from benthic δ18O records are complicated by influences of factors other than temperature, such as the isotope composition of the seawater (δ18Osw), pH, and species-specific physiological effects. Carbonate clumped isotope thermometry (Δ47) has the major advantage that it is independent of the isotope composition of the fluid source, and is not measurably affected by other non-thermal influences. At Utrecht University, we have been working on establishing a late Paleocene-early Eocene deep-sea temperature record from the South Atlantic ocean based on clumped isotopes. On average, we find warmer temperatures than previously appreciated from oxygen isotopes, which challenges longstanding assumptions on the δ18Osw in these past warm ice-free climates. At the onset of the Early Eocene Climatic Optimum, we observe a remarkable temperature increase in the deep Atlantic, reaching up to ~20°C. Concurring with elevated CO2 levels and changes in carbon, nitrogen and sulfur isotope records, this could suggest a reorganization of the ocean system during peak warmth of the early Cenozoic.
Claudia Voigt
University of Cologne (Germany)/CEREGE (France)/University of Almería (Spain)
How triple oxygen isotopes can enhance our understanding of the water cycle
Tracing the water cycle and understanding external forcing and internal feedback mechanisms to climate is of major importance to better predict the consequences of the current anthropogenic climate change. Triple oxygen isotopes are an emerging tool that complements traditional water isotope analysis (hydrogen, oxygen-18). In particular, the triple oxygen isotope system is a powerful tracer of evaporation. This talk aims to provide an overview on opportunities and challenges of triple oxygen isotopes of water for tracinghydrological processes. Specifically, we will explore how triple oxygen isotopes can help to(i) improve lake water balance estimates in semi-arid and arid environments, (ii) constrain the driving factors of grass leaf water balance from diurnal to seasonal scale and its implications for using phytoliths as a paleo-humidity proxy, and (iii) understand processes influencing the atmospheric water balance. The talk summarizes my research carried out during my PhD at the University of Cologne (Germany) and post-doctoral stays at CEREGE (France) and the University of Almería (Spain).
Ilja J. Kocken
Utrecht University
Clumped isotope thermometry in deep time palaeoceanography
This talk explores clumped isotope thermometry in deep time palaeoceanography. I will summarize the main findings of my PhD thesis, which I completed last January in Utrecht, the Netherlands. We have improved the clumped isotope method, and applied it to gain new absolute temperature estimates for records from the surface oceans across critical climate transitions, as well as insights into deep ocean temperature evolution throughout the late Cenozoic. In the most recent IPCC report, palaeoclimate estimates of ECS were used to weigh the model ensemble mean in AR-6, where models with high ECS were given less weight (Forster et al. 2021). Our new insights from clumped isotopes may indicate that this weighing should be reconsidered. Furthermore, scaling sparse estimates of sea surface temperature from particular sites to a global average is hard, and analysing deep ocean temperatures that scale to changes in GMST may be a way forward. As our palaeoclimate studies are used more and more to anchor climate models, we must become ever more diligent in understanding all the factors that drive our proxy systems. Proper treatment of both measurement and systematic uncertainties will be paramount in the next decades of palaeoceanography research.
Niels J. de Winter
Vrije Universiteit Brussel
Seasonality reconstruction based on clumped isotopes in bivalves
Mitigating the anthropogenic driven biodiversity crisis and/or adapting to climate change requires us to obtain a detailed, accurate understanding of the response of Earth’s climate and ecosystems to warming. To understand how these important ecosystems evolve under future climate change, we can look at shallow marine records past warm climates. The shallow marine realm is important for three reasons:
1. Coastal areas form the interface between the terrestrial and marine realm, are home to a large fraction of the Earth’s human population and are economically important regions.
2. Shallow seas contain the most biodiverse ecosystems on the planet, which are very sensitive to environmental change.
3. The continental shelf experiences more extreme (seasonal) climate variability than the open ocean, from where most of our climate records originate.
However, we need archives that record the complex short-term (seasonal scale and beyond) dynamics to fully appreciate their full scale of climate variability.
In this seminar, I will briefly introduce the field of Sclerochronology, the science of reading the skeletal diaries of carbonate-building organisms such as mollusk shells. Following which, I will show how in combination with stable (clumped) isotope thermometry sclerochronology provides us with the tools to understand short-term climate variability in past shallow seas. I will then present case studies showing how sclerochronology contributes to our understanding of past climates and how it can resolve data-model disagreements in high-CO2 worlds. In closing, I will show some of our ongoing projects on the interface between marine biology and inorganic chemistry with which we aim to enhance our understanding of how mollusks build their shells and how changing climate impacts their ecosystem.
Minger Guo
The University of Western Ontario
17O-excess of grass phytoliths across North America accurately records variations in growing-season relative humidity
Atmospheric water vapor is the most important contributor to the natural greenhouse effect and global water cycle. However, Global Climate Models (GCMs) have trouble reconstructing past continental relative humidity (RH) conditions properly. Recent research has shown that the stable isotope signal, 17O-excess of phytoliths (biogenic silica formed in plants’ cells), can be used as an independent proxy for RH, as it can identify leaf water that has been influenced by transpiration. Recent calibration study (Alexandre et al., 2018) in growing chambers have shown a clear relationship between the 17O-excess of leaf phytoliths and controlled RH. This relationship is complicated in natural systems, however, because of climate variations during phytolith formation. This study will illustrate whether the 17O-excess of grass phytoliths is dependent on RH during the growth of plant over the entire growing season in a natural, temperate environment in Ontario and variable climates across North America prairie. The 17O-excess of phytoliths from grasses grown in 17 different regions across North America at the end of the same growing season have been analyzed to discuss the climate effect. The 17O-excess of phytoliths and soil water collected over a three-year period in London, Ontario were also analyzed to discuss effects of seasonality and soil water. Our results show that 17O-excess in leaf phytoliths was significantly correlated with summer average RH at 16 locations across North America where RH ranged from 47 to 76% (17O-excessleaf phytolith = 5.5 RH - 621, R² = 0.79), which hold promise that the 17O-excess of phytoliths is a good proxy for regional RH.
David Bajnai
University of Göttingen
Triple oxygen and clumped isotope thermometry: when to use which?
David's scientific goals are to reconstruct accurate and precise seawater temperatures in geological times to learn about past and future climates. The stable isotope composition of the fossil remains of marine calcifiers, e.g., belemnites and brachiopods, holds information on the surrounding water temperatures. By measuring this, palaeoceanographers can postulate how warm the oceans were millions of years ago. However, vital effects (stable isotope fractionations that happen during mineralisation) and diagenetic alteration of the of the fossils (physical and chemical changes after deposition) bias these temperature estimates. I am using the clumped isotope (∆47 and ∆48) and the triple oxygen isotope (∆17O) proxies to map these effects, correct for them, and thus determine unbiased, accurate temperature reconstructions.
