Department Surface Waters - Research and Management

Biogeochemical cycling at oxic-anoxic boundaries

Blick über das anoxische Südbecken des Zugersees und ein Highlight der chemischen Struktur des Übergangs vom Oxischen zum Anoxischen.


In the absence of oxygen, other elements such as iron and manganese are used in microbial respiration. This fundamentally ties the cycling of these metals to Earth’s major elements (carbon, oxygen, sulfur, nitrogen). This project will investigate the biogeochemical cycling of iron, manganese, and other trace elements, across the oxic-anoxic interface of Lake Zug using chemical, physical, and microbial techniques. Compared to other anoxic lakes, Lake Zug is unique based on its high manganese but low iron and sulfur concentrations, making it a particularly interesting study site.

Anoxic settings are found throughout the modern Earth, and were the major state of Earth’s waters through most of its history. Therefore, these anoxic settings not only allow unique environments for studying modern processes, but also act as analogs to study biogeochemical cycling through Earth’s history.
Another goal of this project is assessing how the chemical tracers we use to reconstruct major states of the Earth (metal abundance, stable isotopes, and speciation) are affected by anoxic conditions in Lake Zug and other anoxic lakes.

Publications

Biogeochemical cycling of trace elements and nutrients in ferruginous waters: constraints from a deep oligotrophic ancient lake

Iron-rich, ferruginous waters were the dominant geochemical regime for most of Earth's history. Modern ferruginous waters are found in stratified, sulfur-poor lakes, and serve as crucial analogs for biogeochemical cycling throughout Earth's past. Here we present the first depth-resolved data of physical structure, nutrients and trace elements from Lake Poso (Indonesia), a deep oligotrophic ancient lake. Lake Poso is ferruginous, with anoxia below ~ 90 m depth, placing it among the world's largest ferruginous lakes. Physical stratification is weaker than other tropical anoxic lakes, indicating sensitivity for paleoclimate reconstructions. Trace elements and nutrients are predominantly shaped by the oxic–anoxic transition. Manganese– and Fe oxyhydroxide–driven biogeochemical cycling occurs at distinct depth horizons, with Co and Ni controlled by Mn and showing shallow release in anoxic waters, while V, Cr, P, and As are controlled by Fe, with release in surface sediments and diffusive transport. Chromium is nonquantitatively removed in anoxic waters, in contrast to widespread assumptions in Cr-based paleoreconstructions. Oxycline U and Se removal corresponds to a local N minimum, suggesting biological reduction and/or uptake. These first ferruginous water Se data also show removal in sediments, indicating sediment signals reflect multiple removal processes and informing Se-based paleoreconstructions, while the absence of sediment U removal contrasts other anoxic basins. A comparison with other ferruginous lakes demonstrates how local influences drive deviations from expectations in other systems, and highlight common, generalizable ferruginous basin features. Therefore, these data will guide research in ferruginous settings across space and time, and improve paleoreconstructions from ferruginous sediment records.
Janssen, D. J.; Damanik, A.; Tournier, N.; Tolu, J.; Winkel, L.; Cahyarini, S. Y.; Vogel, H. (2024) Biogeochemical cycling of trace elements and nutrients in ferruginous waters: constraints from a deep oligotrophic ancient lake, Limnology and Oceanography, doi:10.1002/lno.12687, Institutional Repository