Organic Geochemistry

In general terms the Organic Geochemistry group (led by Heinz Wilkes since 2015) is investigating the origin, properties, and fate of organic matter in the geosphere. At present, our research focuses on three main areas:

> The role of microbial metabolism in biogeochemical key processes

Organic compounds that serve as sources of carbon and energy for microorganisms are of particular interest for our research. Microbial metabolism is a key component in the biogeochemical carbon cycle. Terminal products are the greenhouse gases carbon dioxide and methane which may enter the atmosphere and thus can influence the Earth’s climate system. Full understanding of these processes requires detailed structural knowledge of the organic compounds involved. We use advanced analytical tools to identify metabolic products and elucidate transformation pathways and mechanisms of new reaction types. We are also developing new approaches to trace microbial metabolism at the field level using compositional alteration of organic matter, signature metabolites and stable isotope fractionation. A major focus is currently on anaerobic transformation of hydrocarbons and petroleum which is of utmost relevance with respect to the elevated pollution load of the oceans from both anthropogenic and natural sources.

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> The use of molecular and isotopic proxies in paleoecology and paleoclimatology

Organic geochemical proxies can be useful to evaluate geological archives of past environmental and climatic conditions. In the running project GeoArchives we are applying this approach to sediments from Kalahari salt pans to fill gaps in the continental climate reconstruction of southwest Africa since the last glacial maximum. The salt-pans are local depressions which according to recent results from our project contain sediments which were quasi-continuously accumulated since the late Pleistocene and thus represent valuable new climate archives for the arid regions of southwestern Africa. Besides the reconstruction of vegetation assemblage based on n-alkane distributions and carbon isotopes, compound specific hydrogen isotopes are used to assess precipitation and water availability in the past. A second focus of this project is to better understand how coastal and continental climate changes in this region are connected. For this purpose sediments from Namibian coastal lagoons are analyzed using the same approach.More information...

> The role of anthropogenic microplastics in marine ecosystems

Over the last 60 years global production and consumption of plastics have increased rapidly and led to a steep rise of plastic litter and its accumulation in the marine environment. Physically, chemically, and biologically driven degradation and fragmentation processes result in a constant decrease of the particle size of plastics whereas the number fragments increases continuously. Together with micro-sized primary plastic litter from consumer products these micro-fragments (secondary plastic) below 5 mm are so called “microplastics”. Its ubiquitous presence, persistence, accumulation, interaction potential with environmental pollutants, and size dependent increasing bioavailability in the marine environment have amplified awareness of the potential risks. However, the impact of plastic particles on aquatic ecosystems is far from being understood. In our work group pyrolysis-gas chromatography-mass spectrometry has been established as a novel and reliable method for highly sensitive qualitative and quantitative analysis of common user plastics representing more than 80 % of the actual plastic demand. The technique has already been applied successfully to marine environmental samples like fishes, sediments, and surface water. In addition to the quantification of microplastics the leaching behavior of different additives from plastics into the aquatic system as well as interactions with surfaces and organisms are under scrutiny.

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