The cycle of tungsten (W) in modern environments and implications for W isotopes as palaeoredox proxy

• Applicant: Professor Dr. Carsten Münker, since 1/2024
• Subject Area: Geology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 519341517

The oxygenation of the oceans is distinctly linked to the emergence of life on Earth. In early Earth history the near absence of oxygen (O2) prevented the development of higher life forms. Only the appearance of O2-producing photosynthetic bacteria enabled a stepwise increase in environmental O2-concentrations. The reconstruction of changes in atmospheric and marine O2-abundances mainly relies on the geochemical information preserved in rock records, such as the isotope composition of redox-sensitive elements (e.g. Molybdenum). Tungsten (W) is a promising new candidate among these redox-sensitive elements comprising unique geochemical characteristics such as high solubility in euxinic (H2S-bearing) environments but particle-reactive behaviour in oxic environments. Only the latter characteristic and thus the extension of oxic marine settings seems to cause large stable W isotopic variability. However, for a wider application of stable W isotopes as palaeoredox proxy a more detailed knowledge of the processes that control the abundance of W and its isotope composition in various ecosystems is strongly required. In this project we plan to obtain a holistic picture of the cycling of W (isotopes) in the semi-restricted Baltic Sea. This marginal sea provides key settings to evaluate burial and release mechanisms of W under different redox-regimes and their implications for W isotope systematics and therefore serves as an ideal modern analogue for early Earth’s ecosystems. For example, Baltic Sea water is predominantly oxic but also hypoxic, ferruginous (Fe2+-bearing) and even euxinic in the bottom waters of some deep basins. Our proposed study includes the detailed investigation of sinks and sources of marine W by analysing surrounding bedrocks, river water, sediments, pore water and seawater and also aims to understand the burial path of W down to the mineral scale. This pioneering approach will evaluate potential sedimentary archives for the reconstruction of palaeoenvironmental redox conditions using W isotopes and improve our understanding of the geochemical cycling of W in past and present marine regimes.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Olaf Dellwig
• Ehemaliger Antragsteller: Dr. Florian Kurzweil, Ph.D., until 12/2023