Isotopologue Network for Early Career Researchers (ECR)
Connect with the speakers from current and previous seminars
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.
