Focus of my research

Focus of my research

Temporal Evolution of Global Biogeochemical Cycles

 

The geochemistry of the stable isotopes of sulphur, carbon, nitrogen, oxygen and hydrogen in sediments and sedimentary rocks, biominerals, organic material and waters is at the centre of scientific interest. Research focuses on the documentation and interpretation of spatio-temporal variations of the different isotope signatures, which are used as proxy signals for geological and biologically controlled processes. These geochemical fingerprints document the interaction between the atmosphere, hydrosphere, biosphere and lithosphere, i.e. the interactions within the Earth's system.

Here you will find a summary of selected research projects:

  • Sulphur cycling in subduction zones

    Submarine hydrothermalism at intraoceanic plate boundaries and in back-arc basins shows a significantly higher variability than at mid-ocean ridges, resulting from the fundamental differences in the plate tectonic context. Sulphur as an important component in hydrothermal systems is also highly variable in terms of concentration, speciation (sulphide, sulphate, elemental sulphur, intermediate sulphur species) and isotopic composition. The sulphur isotopes of hydrothermal fluids and precipitates reflect the various sulphur sources and sulphur turnover processes. Principal sources are seawater sulphate, sulphur in rocks of the ocean floor and a direct magmatic contribution such as sulphur dioxide. Turnover processes are thermochemical sulphate reduction, water-rock interaction, SO2 disproportionation and synproportionation as well as microbially mediated sulphur turnover.

    The project focuses on the multiple sulphur isotopes (32S, 33S, 34S, and 36S) of selected hydrothermal systems along the Kermadec-Tonga island arc system in the Western Pacific. The objectives include the (isotopic) geochemical characterisation of the hydrothermal fluids and precipitates and the identification of the different sulphur sources and sulphur turnover processes, with a focus on microbial sulphur turnover. For this purpose, extensive sample sets were collected during two cruises along the Kermadec-Tonga island arc and the Northeast Lau Basin (F/S SONNE cruises SO253 and SO263). Samples include hydrothermal fluids and precipitates (various sulphides, sulphates, elemental sulphur), hydrothermal plumes, seawater, lithologically variable oceanic crustal rocks and biological samples. The overall aim of the study is to extend our knowledge of hydrothermal systems at intraoceanic plate boundaries and in back-arc basins, focussing on sulphur as an important element in inorganic and microbially controlled turnover processes.

  • The impact of coal mining on atmosphere, soil, surface water and groundwater

    The impact of coal mining on our environment was and is multi-layered. Surface and groundwater (discharge of mine water, seepage of decomposition products from coke production), soil (wind-blown coal dust) and the atmosphere (coal combustion) are equally affected. In addition to the elements carbon and sulphur, anthropogenic contributions include a wide range of organic pollutants and metals. The aim of our investigations is always to clearly differentiate anthropogenic pollution from the natural, geogenic background. Geochemical methods allow quantifying the pollution. Isotope geochemical investigations are used to clearly identify the origin of dissolved or particulate matter and to characterise relevant turnover processes. A corresponding approach of multiple hydro-, geo- and isotope-geochemical analyses also enables the determination of natural attenuation or monitoring the success of remediation methods. Studies on this overarching topic are being carried out both in Germany and in China.

  • Biogeochemistry of methane seeps on the sea floor

    In many regions, the ocean floor is characterised by methane seepage. This methane is the product of microbial and/or thermal turnover of organic carbon in the sediment. Given the right temperature and pressure conditions, methane is fixed in the sediment in the form of so-called methane hydrates, or the gaseous methane migrates towards the seabed and then escapes into the water column. In the sediment and in the water column, the methane is usually converted microbially under changing redox conditions. Under anoxic conditions, the process of sulphate-driven anaerobic methane oxidation plays a particularly important role. This microbially controlled process links the sulphur and carbon cycles. Preservable products in the sediment, so-called authigenic mineral formations, are carbonates and pyrite. Isotope geochemical studies of these minerals provide clear evidence of respective reactions and allow the prevailing environmental conditions to be characterised. Investigations on sediment cores and pore waters from the South China Sea and the Marmara Sea are being carried out on this overarching topic.

  • Seasonality of biogeochemical processes in stratified lakes

    Seasonally stratified lakes offer the opportunity to study changes in relevant biogeochemical processes under changing redox conditions. As natural laboratories, the two large still waters (Großes Heiliges Meer and Erdfallsee) in a nature reserve near Hopsten, North-Rhine Westphalia, offer excellent conditions for this research. In both lakes, a stable stratification of the water column develops over the course of the early summer due to temperature changes. As a result, the lower half of both lakes is oxygen-free in late summer/autumn. Hydrochemical and isotope geochemical vertical profiles through the water column and the examination of sediment cores clearly demonstrate the turnover of the organic material available in the lake through aerobic respiration (in the upper half) and anaerobic sulphate reduction (in the lower half). Methane in the water column and in the sediment also provides evidence of microbial methane formation in the sediment. Investigations at different times of the year illustrate the seasonal change from stagnation to full circulation and the associated ups and downs of redox zonation and the relevant biogeochemical material turnover.

  • Investigations on the sulphur cycling in hydrothermal systems of the Tyrrhenian Sea

    Based on the findings on sulphur cycling at mid-ocean ridges (own investigations at the Mid-Atlantic Ridge), multiple sulphur isotopes in hydrothermal fluids, massive sulphides and sulphates as well as sediments and pore waters are used to characterise the origin and turnover processes of sulphur in two target regions in the Tyrrhenian Sea: the submarine hydrothermal exhalations and massive sulphides at Palinuro and at Panarea. Especially in the sediments, the focus is on the differentiation between clear hydrothermal precipitates and microbial sulphur turnover.

  • Peering into the Cradle of Life

    One of the most exciting questions in the earth and life sciences is where and when life began on our planet. Well-preserved sedimentary rocks with an age of 3.5 billion years already contain clear traces of life: microscopically small structures of carbonaceous material, which are interpreted as microfossils, stromatolites as well as geochemical and isotope geochemical evidence of a complex microbial ecosystem already in the early phase of the Earth's history. Older evidence is missing due to the significant overprinting of an already sparse rock archive.

    The Barberton Greenstone Belt in southern Africa represents one of the best preserved sequences of supracrustal rocks on Earth with an age between 3.5 and 3.2 billion years. The rock sequence thus provides an insight into the physico-chemical conditions of near-surface habitats in which early life evolved. As part of the International Continental Scientific Drilling Programme (ICDP), the 'Peering into the Cradle of Life' project drilled into this rock sequence in 2011 and 2012 in order to obtain well-preserved sample material for a broad spectrum of geoscientific investigations by an international team of researchers.

    Multiple sulphur isotopes are established as a unique biosignature, both in present-day and especially in geologically ancient systems, including the well-preserved sedimentary sequences in the Barberton Greenstone Belt. In addition, the mass-independent fractionation of sulphur isotopes is an indicator of atmospheric composition, especially with regard to oxygen concentration. Consequently, multiple sulphur isotopes and complementary geochemical analyses will be used to take a look into the cradle of life.
    Further links: Barberton Drilling Project - 1 and Barberton Drilling Project - 2

    Peering into the Cradle of Life

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  • Multiple sulphur isotope analyses reflecting the atmosphere-ocean evolution in the Archean and Palaeoproterozoic

    A very significant increase in our understanding of the global sulphur cycle in early Earth's history can be achieved by analysing multiple sulphur isotopes in Archaean and early Palaeoproterozoic sedimentary rocks. Possible implications are significantly higher than those that were/can be obtained from classical δ34S data. In the sense of a chemostratigraphic approach, important sedimentary sequences in southern Africa, Western Australia and Canada with a geological age >2000 Ma are investigated. Corresponding isotope time series from the simultaneous measurement of all four stable sulphur isotopes (32S, 33S, 34S, and 36S) will make it possible to shed light on critical questions of early Earth history in unprecedented detail: temporal variations in atmospheric composition, the evolution of metabolic pathways of sulphur, and the functioning of the global sulphur cycle as a whole. All this information will significantly advance our overall understanding of the function of the Earth system in early Earth history.

    To determine all four sulphur isotopes, the various sulphur species are first extracted from the original sample and precipitated as silver sulphide. This is then converted to sulphur hexafluoride for the mass spectrometric measurement. As part of a DFG-funded research project, the necessary analytical methods were established, in particular a fluorination system and the associated mass spectrometry.

  • FAR-DEEP: In search of oxygen in northern Russia

    The transition from the Archean to the Proterozoic (approx. 2500 million years ago) is characterised by diverse geological, geochemical and climatic changes. Part of this sequence of substantial changes in the Earth system was a significant increase in the oxygen concentration of the atmosphere-ocean system in the early Palaeoproterozoic around 2350 million years ago (G.O.E. - Great Oxidation Event). This change in the composition of the atmosphere led to the beginning of oxidative weathering on the continents, to an increase in oxygen concentration at least in the near-surface ocean and, as a consequence, to a spatial shift in the biologically controlled redox processes in the water column. The previously predominantly anaerobic processes shifted to the anoxic deep water or the sediment.

    As part of the International Continental Deep Drilling Programme (ICDP), the FAR-DEEP project (Fennoscandian Arctic Russia - Drilling Early Earth Project) will carry out 15 boreholes with a planned total core length of 3740 m in three regions of northern Russia and Karelia in 2007. These boreholes will allow studying the aforementioned changes in the transition from the Archean to the Proterozoic by providing fresh rock material for geological and, above all, geochemical investigations. The work is also being funded by the German Research Foundation.

    Further links: FAR-DEEP homepage and Spiegel-Online article

  • Reconstruction of the temporal evolution of the marine sulphur cycle, reflected by the sulphur isotopic composition of structurally bound trace sulphate in biogenic carbonates and inorganic limestones.

    An understanding of the temporal evolution of the marine sulphur cycle has been achieved by analysing the sulphur isotopic composition of seawater. The classic approach is to analyse marine evaporites from the geological past. As chemical sediments, sulphates represent the isotopic signature of the dissolved seawater sulphate. However, due primarily to the high weatherability of evaporites, but also to periods of non-deposition, the temporal resolution over the course of Earth's history is very fragmentary. In addition, the age constraints of evaporites are often poor.

    Marine carbonates contain sulphate, which is structurally incorporated into the crystal lattice during carbonate precipitation. In biogenic carbonates in particular, concentrations are high enough to allow the sulphur isotopic composition of this trace sulphate to be analysed. At the same time, the calcareous fossils can be used for biostratigraphic purposes. This approach enables the creation of a new time series for the sulphur isotopic composition of Phanerozoic seawater. The improved temporal resolution and greater completeness for this data set results in the documentation of previously unknown temporal variations. The investigations on the sulphur isotopic composition of trace sulphates are funded by the German Research Foundation.

  • The sulphur isotopic composition of dissolved and solid sulphur species in fluids, mineral precipitates, sediments and rocks of the Mid-Atlantic Ridge

    Hydrothermal systems at mid-ocean ridges document the interaction between the hydrosphere, lithosphere and biosphere. Sulphur participates in both inorganic and microbially controlled processes in these vent systems. Sulphur isotope analyses provide important information on sulphur cycling. The principal end members of the sulphur cycle at mid-ocean ridge systems are seawater sulphate (δ34S of +21‰) and basaltic sulphur (δ34S of +0‰). Analysing the sulphur isotope signatures of the different sulphur compounds in fluids, hydrothermal precipitates, altered mafic and ultramafic rocks as well as the associated vent fauna and quantifying the isotopic fractionation will ultimately lead to a comprehensive understanding of the corresponding material fluxes. The aim of the project is to gain a qualitative and quantitative understanding of the sulphur cycling at the Mid-Atlantic Ridge. Long-term observations are an important aspect of this in order to reveal temporal changes in the physico-chemical framework conditions and the resulting changes in the chemical and isotopic composition of the vent fluids and the entire ecosystem.

  • The chemical evolution of the ocean-atmosphere system in the late Neoproterozoic and early Cambrian

    The late Neoproterozoic (Cryogenian and Ediacarian) and the transition to the Cambrian are characterised by substantial changes in paleogeography, in the chemical composition of the ocean-atmosphere system, and in the evolutionary history of life. These substantially affect the global geochemical cycles of carbon and sulphur. Through geochemical (C, S, Fe) and isotope geochemical (C, O, S) studies of relevant sedimentary sequences in southern China and Namibia, these temporal variations will be characterised and quantified.

  • Quantification and geochemical characterisation of mass fluxes and chemical weathering rates in river catchments of the northern Rhenish Slate Mountains

    The chemical composition of rivers reflects the weathering in the catchment area. The aim of a study in the northern Rhenish Slate Mountains is to quantify recent mass fluxes using runoff data and chemical analyses of the dissolved and particulate river load. For this purpose, a selection of main and trace elements as well as some stable isotopes are measured. In parallel to the chemical characterisation of the river load, the erosion rates are determined using cosmogenic nuclides*, specifically the investigation of 10Be in quartz from river sediments. The rates of erosion and sediment transport will be compared with the amounts of sediment that have been deposited in river basin reservoirs over decades. The planned investigations will allow quantitative statements to be made on the late Quaternary landscape evolution of a typical low mountain range in Central Europe as well as on the influence of physical and chemical weathering on the composition of river loads.

    (*joint research project with Prof. Dr. R. Hetzel)

  • The terrestrial carbon cycle in the Upper Paleozoic.

    The evolution of land plants and their rapid spread across continents in the Upper Paleozoic led to substantial changes within the global carbon cycle. The latter is divided into a marine and a terrestrial part, with the characterisation and quantification of the terrestrial carbon cycle being the central topic of this research project. This is done by analysing the carbon isotopic composition of organic carbon, using well-preserved plant fossils as sample material. The connections between the carbon cycle and other geochemical cycles identify important interactions resulting from the colonisation of the continents by land plants and the flux of detrital terrestrial organic matter into the marginal marine sedimentation areas. This study on the terrestrial carbon cycle is funded by the German Research Foundation. The project is part of the DFG priority program "Evolution of the Earth system during the Younger Paleozoic as reflected in sediment geochemistry".

  • Characterisation of the sedimentary sulphur cycle in the Paleozoic.

    Temporal variations of the marine sulphur cycle in the Paleozoic will be identified by analysing structurally bound sulphate of biogenic carbonates, sedimentary sulphides and organically bound sulphur. In particular the biologically controlled processes are in the focus of this investigation, as they enable appropriate identification and characterisation through often substantial fractionations of the sulphur isotopes. Initial results already demonstrate the detail of possible interpretations in connection with a species-dependent differentiation of the sedimentary sulphur pool. The interaction with the carbon cycle leads to interesting questions, especially with regard to the colonisation of the continents by land plants in the Upper Paleozoic. The study of the Paleozoic sulphur cycle is being funded by the German Research Foundation. This project is part of the DFG priority program "Evolution of the Earth system during the Younger Paleozoic as reflected in sediment geochemistry". The studies aim at documenting the geochemistry of the stable isotopes of carbon, sulphur and oxygen in sediments and sedimentary rocks, biominerals and organic material over geological time periods. These signatures are used as proxy signals, or geochemical fingerprints, to reconstruct important developments in the biosphere, hydrosphere, lithosphere, and atmosphere. In combination with the stable isotopes, the isotopes of strontium are also used here.