Research: Low-Temperature Aqueous Geochemistry
Elevated concentrations of “exotic” trace elements in surface-, ground- and drinking water are potentially hazardous, but might also be used as pseudo-natural tracers. Gadolinium is such an exotic trace element. All river and lake waters in densely populated and developed countries are contaminated by a Gd-compound used as a medical diagnostic in magnetic resonance imaging. A current project aims at quantifying the amounts of anthropogenic Gd delivered to the North Sea by major German rivers and at utilizing anthropogenic Gd to locate major leakage sites in municipal sewage systems. Another project involving a variety of laboratory experiments aims at helping to understand how trace metals in aquatic systems are controlled in their solid-solution distribution by various reactions (complexation, precipitation, sorption on solids, and redox reactions). Trace metals can be either essential or toxic and some are significantly enriched in certain deposits. Our special interest lies in the investigation of redox-sensitive trace metal couples, such as the partly essential element selenium and the toxic metal tellurium
The research activity of the group in the field of marine geochemistry forms the link between geosciences and oceanography. At present and in the near future, the focus of this work lies on the geochemical investigation of marine hydrothermal systems. The volcanically active mid-ocean ridges play a very special geological and also biological role in the oceans. Approximately 90% of the volcanism on Earth is concentrated along this 60.000 km long plate boundary, releasing ca. 25% of the Earth´s inner heat. Most present-day ore-forming processes are also occurring along these spreading axes, associated with hydrothermal systems which exert a strong influence on the chemistry of seawater and support unique exotic ecosystems. Also hot spot systems and back-arc basins can host hydrothermal systems. The circulation of fluids in the oceanic crust and the emerging hot, mineral- and gas-rich fluids from the ocean floor are the fundament of the unique hydrothermal communities. Within the scope of GEOTRACES, which is an international programme to improve the understanding of biogeochemical cycles and large scale distribution of trace elements and their isotopes in the marine environment, we focus on the elements Ti-Zr-Hf, V-Nb-Ta, and Cr-Mo-W. These transition metals are of biological importance as micronutrients or microtoxins. Additionally several of them contribute to the formation of valuable ore deposits on the seafloor such as ferromanganese nodules and crusts. Some of these metals also serve as proxies for elemental sources into the ocean, water mass movements or paleo redox conditions. As they represent important resources for many high-tech applications, they might also be target elements for future marine mining and might enter the ocean as future contaminants.
Research: Chemical Evolution of Atmosphere and Oceans
The chemical composition of the Earth’s atmosphere and oceans underwent several significant changes resulting from events as diverse as meteorite impacts, onset of oxic photosynthesis, and supercontinent break-up, for example. Current projects focus on the utilization of marine sedimentary iron and manganese oxides and carbonates from southern Africa and Western Australia, and on cherts and phosphates as recorders of atmospheric change and evolution of life on Early Earth. These projects are closely connected with studies of the genesis and distribution of major sedimentary ore deposits (Fe, Mn). Studies look at the systematics of directly or indirectly redox-sensitive elements and element pairs, such as Ce-Eu-REE, Se-Te, Th-U, Ge-Si.