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Using trace metal isotopes to understand ocean biogeochemistry: ancient and modern

English title Using trace metal isotopes to understand ocean biogeochemistry: ancient and modern
Applicant Vance Derek
Number 184873
Funding scheme Project funding (Div. I-III)
Research institution Institut für Geochemie und Petrologie ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geochemistry
Start/End 01.04.2019 - 31.03.2023
Approved amount 1'066'722.00
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Keywords (5)

Transition metals; Isotope geochemistry; Earth history; Biogeochemistry; Ocean chemistry

Lay Summary (German)

Lead
Anwendung von Spurenmetallisotopen zum Verständnis ozeanischer Biogeochemie - vergangen und modern
Lay summary

Chemische Prozesse in den Ozeanen sind essentiell für die Bewohnbarkeit unseres Planeten.  Das Leben auf der Erde entstand höchstwahrscheinlich in den Ozeanen. Die Ozeane enthalten zudem das grösste Reservoir an Kohlenstoff, welches mit der Atmosphäre auf kurzen und mittleren Zeitskalen interagiert. Biologische Prozesse in den Ozeanen und die Produktion verschiedener Sedimente helfen bei der Regulierung des wichtigen Treibhausgases Kohlenstoffdioxid in der Atmosphäre. 

Der ozeanische Pool biologisch wichtiger Elemente – Kohlenstoff, aber auch Sauerstoff, Phosphor, Stickstoff und Silizium, sowie Spurenelemente wie Eisen, Zink, Molybdän und Nickel –  ermöglicht Leben in den Meeren. Die Entwicklung der Ozeanchemie, aufgezeichnet in marinen Sedimenten, ist eine der wichtigsten Informationsquellen bezüglich Umweltveränderungen durch die Erdgeschichte. Der Fokus dieses Projektes sind Spurenelemente und ihre Isotope in marinen Sedimenten und was sich anhand ihrer Aufzeichnungen über die Umweltbedingungen während der 4.6 Milliarden Jahre Erdgeschichte schliessen lässt.

Die Anwendung der Sedimentgeochemie von Spurenelementen  – Metalle wie Magnesium, Eisen, Zink, Nickel sowie ihre stabilen Isotopen – ist ein Kernanliegen der Forschungsgruppe für Erdoberflächengeochemie an der ETH Zürich. Wir haben die Entwicklungen in dieser neuen Subdisziplin der Isotopengeochemie vorangetrieben und mitgeprägt. Hier streben wir ein vertieftes Verständnis der Metallisotopensysteme an, um sie zu zuverlässigen Archiven der Erdgeschichte  zu machen. Dazu verwenden wir Experimente und Beobachtungen des modernen Systems. Wir wenden die Isotopensysteme auch an,  um zwei Schlüsselperioden der Erdgeschichte zu verstehen, welche geprägt sind durch bedeutende Veränderungen der Umwelt und der Biosphäre.

Direct link to Lay Summary Last update: 01.04.2019

Lay Summary (English)

Lead
Using trace metal isotopes to understand ocean biogeochemistry: ancient and modern
Lay summary

Chemical processes in the ocean are a vital part of making our planet habitable. Life on Earth almost certainly began in the oceans. The ocean contains the largest store or carbon that is exchangeable with the atmosphere on short to medium timescales.  Biological processes in the ocean, and the production of different kinds of ocean sediments, help to regulate the important greenhouse gas, carbon dioxide, in the Earth’s atmosphere.

The oceanic pool of biologically important elements – carbon, but also oxygen, phosporous, nitrogen and silica, as well as trace metals like iron, zinc, molybdenum and nickel, support life in the oceans. In addition, the evolution of ocean chemistry, as recorded in sediments formed in the ocean, provides one of our main sources of information on environmental change through Earth history. The focus of this project is the trace metal chemistry – and isotope geochemistry – of marine sediments, and what they can tell us about the environment of the surface Earth through the 4.6 billion years of its history.

The use of the sedimentary geochemistry of trace metals in this way – metals like magnesium, iron, zinc, nickel – as well as their stable isotope systems - is one of the core research pursuits of the Earth Surface Geochemistry group at ETH Zürich, and we have helped to pioneer this new sub-discipline of isotope geochemistry. Here we seek to continue our effort to develop these metal isotope systems into more faithful records of Earth history, through experiments and observations of modern systems. We also aim to use them to understand two key periods of Earth history that have seen major changes in both the Earth’s environment and its biosphere.

Direct link to Lay Summary Last update: 01.04.2019

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Abstract

The biogeochemistry of the oceans is key to the regulation of the Earth system. For example, the inputs to the oceans respond to important processes such as chemical weathering. The oceanic reservoir of both major nutrients (phosphate, nitrate and silica) and of the trace metal micronutrients (e.g. Fe, Zn, Mo, Ni), have supported the only life on the planet for most of its history. This oceanic biosphere controls crucial aspects of the surface chemistry of the Earth: for example, burial of fixed carbon regulates the pH and the redox state of the oceans and atmosphere. In addition, the secular evolution of ocean biogeochemistry, as recorded in the authigenic and biogenic fractions of chemical sediments, provides one of our main records of environmental change through Earth history. The isotope geochemistry of these sedimentary products is an important component of these records, and isotope studies of elements such as oxygen, carbon, sulphur and nitrogen have fundamentally changed our view of Earth evolution, helping to identify and quantify profound environmental change such as the Great Oxidation Event, Snowball Earth episodes, major perturbations of the carbon cycle associated with Mesozoic volcanism, anoxia and mass extinction, and the descent into the icehouse conditions of the Cenozoic. These issues are the focus of research in the Earth Surface Geochemistry group at ETH Zürich, and the topic of this research proposal. The tools we use, however, go beyond the “traditional” stable isotope systems listed above. Specifically, this proposal seeks to further develop and apply the isotope systems of elements that have been available for study only relatively recently, the metal stable isotope systems that are still denoted “non-traditional” and summarised in the recent volume of Reviews in Mineralogy and Geochemistry (e.g. [1-3]). A key thrust of this proposal is that, though the current utility and future potential of these relatively new isotope systems are already clear, our quantitative understanding of the processes that fractionate them, the operation of their modern cycles, and the best ways to apply them to the study of Earth history, are all still very much under development. We propose 5 sub-projects, summarised below.Sub-project A (post-doctoral researcher): to use oceanic records of Mg isotopes, in combination with an improved understanding of the budget, to clarify the link between dolomitic sedimentation and climate.Sub-project B (post-doctoral researcher): to continue work to establish the controls on biologically-active metal isotopes in the water column of the modern water column, the basis for their application to the past.Sub-project C would fund a new doctoral student to undertake a systematic study of a neglected aspect of oceanic trace metals, the sediment-porewater system, emerging as one of the key players in oceanic budgets.Sub-project D will allow a late-starting doctoral student on our previous SNF project to complete her investigation of trace metals in carbonates, and the application of carbonate-based records to Earth history.Sub-project E will allow a late-starting doctoral student on our previous SNF project to continue her work on the modern controls on the Ni isotope budget of the ocean. This project will also apply the new understanding gained to one of the most remarkable periods of Earth history, the late Archean and early Proterozoic, with the primary aim of using a multi-metal isotopic approach to track a hypothesised switch away from an ocean and atmosphere dominated by methanogenic organisms.
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