idw – Informationsdienst Wissenschaft

Nachrichten, Termine, Experten

Grafik: idw-Logo
Science Video Project
idw-Abo

idw-News App:

AppStore

Google Play Store



Instanz:
Teilen: 
10.08.2020 11:00

Exact climate data from the past

Markus Bernards Public Relations und Kommunikation
Goethe-Universität Frankfurt am Main

    FRANKFURT. Corals and cave carbonates are important archives of past climate. This is because the composition of these carbonate deposits can reveal the temperatures that prevailed at the Earth’s surface at the time they formed. An international team of geoscientists led by Goethe University Frankfurt, Germany, has now developed a new method that makes it possible to identify whether the composition of these deposits was exclusively controlled by temperature, or if the formation process itself exerted an additional control. The new method allows scientists to determine past Earth surface temperatures more reliably.

    Corals precipitate their calcareous skeletons (calcium carbonate) from seawater. Over thousands of years, vast coral reefs form due to the deposition of this calcium carbonate. During precipitation, corals prefer carbonate groups containing specific variants of oxygen (chemical symbol: O). For example, the lower the water temperature, the higher the abundance of a heavy oxygen variant, known as isotope 18O, within the precipitated carbonate. Unfortunately, the 18O abundance of the seawater also influences the abundance of 18O in the calcium carbonate – and the contribution of 18O from seawater cannot be resolved when determining temperatures based on carbonate 18O abundances alone.

    A great step forward was the discovery that the isotopic composition of the precipitated carbonate allows temperature determinations independent of the composition of the water if the abundance of a specific, very rare carbonate group is measured. This carbonate group contains two heavy isotopes, a heavy carbon isotope (13C) and a heavy oxygen isotope (18O) which are referred to as “clumped isotopes”. Clumped isotopes are more abundant at lower temperatures.

    However, even with this method there was still a problem: The mineralization process itself can affect the incorporation of heavy isotopes in the calcium carbonate (kinetic effects). If unidentified, the bias introduced by such kinetic effects leads to inaccurate temperature determinations. This particularly applies for climatic archives like corals and cave carbonates.

    An international research group led by Professor Jens Fiebig at the Department of Geosciences at Goethe University Frankfurt has now found a solution to this problem. They have developed a highly sensitive method by which – in addition to the carbonate group containing 13C and 18O – the abundance of another, even rarer carbonate group can be determined with very high precision. This group also contains two heavy isotopes, namely two heavy oxygen isotopes (18O).

    If the theoretical abundances of these two rare carbonate groups are plotted against each other in a graph, the influence of the temperature is represented by a straight line. If, for a given sample, the measured abundances of the two heavy carbonate groups produce a point away from the straight line, this deviation is due to the influence of the mineralization process.

    David Bajnai, Fiebig’s former PhD student, applied this method to various climatic archives. Among others, he examined various coral species, cave carbonates and the fossil skeleton of a squid-like cephalopod (belemnite).

    Today, Dr. Bajnai is a post-doctoral researcher at the University of Cologne. He explains: “We were able to show that – in addition to temperature – the mechanisms of mineralization also greatly affect the composition of many of the carbonates that we examined. In the case of cave carbonates and corals, the observed deviations from the exclusive temperature control confirm model calculations of the respective mineralization processes conducted by Dr. Weifu Guo, our collaborator at the Woods Hole Oceanographic Institution in the USA. The new method, for the first time, makes it possible to quantitatively assess the influence of the mineralization process itself. This way, the exact temperature of carbonate formation can be determined.”

    Professor Jens Fiebig is convinced that the new method holds great potential: “We will further validate our new method and identify climatic archives that are particularly suitable for an accurate and highly precise reconstruction of past Earth surface temperatures. We also intend to use our method to study the effect that anthropogenic ocean acidification has on carbonate mineralization, for instance in corals. The new method might even allow us to estimate the pH values of earlier oceans.” If all this succeeds, the reconstruction of environmental conditions that prevailed throughout Earth’s history could be greatly improved, he adds.


    Wissenschaftliche Ansprechpartner:

    Professor Jens Fiebig
    Department of Geosciences
    Goethe University Frankfurt
    Tel.: +49 (0) 69 798 40182
    Jens.Fiebig@em.uni-frankfurt.de

    Dr. David Bajnai
    Institute of Geology and Mineralogy
    University of Cologne
    Tel.: +49 (0)221 470 89829
    David.Bajnai@uni-koeln.de

    Dr. Weifu Guo
    Department of Geology and Geophysics
    Woods Hole Oceanographic Institution
    Woods Hole, MA
    USA
    Tel.: +1 508 289 3380
    wfguo@whoi.edu


    Originalpublikation:

    Publication: David Bajnai, Weifu Guo, Christoph Spötl, Tyler B. Coplen, Katharina Methner, Niklas
    Löffler, Emilija Krsnik, Eberhard Gischler, Maximilian Hansen, Daniela Henkel, Gregory D. Price, Jacek Raddatz, Denis Scholz, Jens Fiebig: Dual clumped isotope thermometry resolves kinetic biases in carbonate formation temperatures, Nature Communications, DOI 10.1038/s41467-020-17501-0, http://www.nature.com/ncomms


    Bilder

    Merkmale dieser Pressemitteilung:
    Journalisten, Lehrer/Schüler, Studierende, Wirtschaftsvertreter, Wissenschaftler, jedermann
    Biologie, Chemie, Meer / Klima, Umwelt / Ökologie
    überregional
    Forschungs- / Wissenstransfer, Wissenschaftliche Publikationen
    Englisch


     

    Hilfe

    Die Suche / Erweiterte Suche im idw-Archiv
    Verknüpfungen

    Sie können Suchbegriffe mit und, oder und / oder nicht verknüpfen, z. B. Philo nicht logie.

    Klammern

    Verknüpfungen können Sie mit Klammern voneinander trennen, z. B. (Philo nicht logie) oder (Psycho und logie).

    Wortgruppen

    Zusammenhängende Worte werden als Wortgruppe gesucht, wenn Sie sie in Anführungsstriche setzen, z. B. „Bundesrepublik Deutschland“.

    Auswahlkriterien

    Die Erweiterte Suche können Sie auch nutzen, ohne Suchbegriffe einzugeben. Sie orientiert sich dann an den Kriterien, die Sie ausgewählt haben (z. B. nach dem Land oder dem Sachgebiet).

    Haben Sie in einer Kategorie kein Kriterium ausgewählt, wird die gesamte Kategorie durchsucht (z.B. alle Sachgebiete oder alle Länder).