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Hinrichs Lab - MARUM-GB3

MARUM - GB3: Transformation of matter and the role of microbes in subsurface sediments

Duration:July 2009 - June 2013
Funding:Deutsche Forschungsgemeinschaft (DFG)
DFG-Research Center/Excellence Cluster "The Ocean in the Earth System" (MARUM)
Principal Investigator(s):Kai-Uwe Hinrichs
Involved scientists in the Hinrichs Lab:Yu-Shih Lin, Marcus Elvert, Verena Heuer
Partners:A. Boetius (Max-Planck-Institut für Marine Mikrobiologie/MARUM, Bremen), B. Brunner (Max-Planck-Institut für Marine Mikrobiologie/MARUM, Bremen), T. Ferdelman (Max-Planck-Institut für Marine Mikrobiologie/MARUM, Bremen), Boris Koch (Alfred-Wegener-Institut/MARUM, Bremerhaven), Matthias Zabel (MARUM/Universität Bremen)
Abstract

In the last decade, research on the marine deep biosphere has provided first insights into the taxonomic composition and distribution of microbial populations in the subseafloor and into the metabolic rates that sustain them. With this project, we aim to (1) constrain the geomicrobial relevance of novel reactions coupling the sedimentary C- and S-cycles, (2) examine how and what fraction of refractory organic carbon is being utilized by microbial activity, and (3) test and apply new isotopic assays for constraining rates and importance of S-based respiration. Our studies employ a combination of field observations and laboratory-based experiments with subsurface sediments.

(1) Novel reactions coupling sedimentary C and S cycles: We have recently observed a range of both biologically and abiologically mediated reactions that result in the formation of alkylated sulfur compounds under reducing conditions, one of them involving formation of dimethyl sulfide (DMS) from CO2, H2, and H2S. Biological formation of these compounds could potentially provide sufficient energy to sustain microbial growth but also provides potential substrates for the formation of corresponding hydrocarbons. The spectrum of reactions and products appears to be linked to the type of sediment, microbial community, and induced physicochemical condition. In this project we investigate (i) both biological and abiological mechanisms involved in production of alkylated S-compounds, (ii) their role as substrates for microbial communities, (iii) and the relevance of the underlying processes in marine sediments.
(2) Chemical alteration of refractory organic matter by subsurface microbial communities: Subsurface microbial seem to depend on the slow degradation of refractory organic matter as an energy and carbon source. Constraining the alteration of organic matter on a chemical level will be key to understanding the limitations of subsurface microbial activity and its role in the geological carbon cycle. We monitor changes in the chemical composition of dissolved organic matter (DOM) during incubations of deeply buried sediments by ultra-high Resolution Mass Spectrometry (FT-ICR-MS). Its ultra-high mass resolution enables simultaneous detection of ~2000 compounds and determination of their elemental composition in typical marine pore water samples (Schmidt et al., 2009). In long-term incubations, we test how microbial processes influence the molecular spectrum of DOM.

(3) The dual isotope system of sulfate as a recorder of S-based respiration: Sulfate is a major source of oxidizing power in the global redox balance of the ocean, including the subseafloor ocean, and involves not only dissolved sulfate in seawater, but also sulfatebearing minerals such as barite, gypsum, carbonates, and phosphorites. Our research indicates that the dual S-O isotope systematics of sulfate holds great promise to quantitatively constrain sulfur-based respiratory processes, even when these occur at slow rates that are inaccessible to conventional techniques for rate determination. Therefore, we use this tool for the exploration of the relative importance of oxidative and reductive sulfur cycling in the deep biosphere. In more extreme deep biosphere environments, large excursions towards high temperature or low pH may occur and may impact microbial S-O isotope fractionation. Therefore, additional laboratory studies help us to address how factors such as pH and temperature affect abiotic and microbial isotope effects. This part of the project is lead by Dr. T. Ferdelman at the Max-Planck-Institute for Marine Microbiology in Bremen.

The project is following up MARUM B2.