Project Description
Iron (oxy)hydroxide minerals play a dual role in marine sediments: they effectively bind and sequester organic matter under oxic conditions, yet also serve as electron acceptors during microbial iron reduction in anoxic environments. Despite their importance, the rates at which iron oxides are reduced when bound to organic matter remain poorly constrained—an essential gap in understanding iron-mediated organic matter cycling. In this project, we will employ a novel isotope-based technique to accurately measure iron reduction rates. This method allows for sensitive detection independent of ferrous iron precipitation, thereby enabling quantification of carbon oxidation and sequestration associated with iron oxide minerals, and in addition microorganisms involved in these processes will be identified too using molecular ecology methods.
In order to define the selectivity of iron oxides for adsorbing distinct organic matter molecules, we will characterize the molecular composition of organic matter associated with different iron oxide phases using high-resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICR-MS). Model incubations using glycans derived from phytoplankton and macroalgae adsorbed onto iron oxides will be conducted to trace microbial activity via RNA-based stable isotope probing. Experiments will utilize primarily sediments from the North Sea reflecting a gradient of different particle sizes, but look as well into iron oxides derived from hydrothermal vents as an important source for iron in the oceans. Our project will contribute to a better understanding of the role of iron cycling in organic matter oxidation, when iron oxide mineral sorption is involved.
Further Reading
- Lalonde, K., Mucci, A., Ouellet, A. et al. Preservation of organic matter in sediments promoted by iron. Nature 483, 198–200 (2012). doi: 10.1038/nature10855
- Moore, O.W., Curti, L., Woulds, C. et al. Long-term organic carbon preservation enhanced by iron and manganese. Nature 621, 312–317 (2023). doi: 10.1038/s41586-023-06325-9
- Dong, H., Zeng, Q., Sheng, Y. et al. Coupled iron cycling and organic matter transformation across redox interfaces. Nat Rev Earth Environ 4, 659–673 (2023). doi: 10.1038/s43017-023-00470-5
- Chen, Y., Dong, L., Sui, W. et al. Cycling and persistence of iron-bound organic carbon in subseafloor sediments. Nat Commun 15, 6370 (2024). doi: 10.1038/s41467-024-50578-5
Modalities
The doctoral project will be supervised by Michael Friedrich (University of Bremen) and Matthias Zabel (University of Bremen) within the working group “Microbial Ecophysiology” at the MARUM – Center for Marine Environmental Sciences at the University of Bremen. The remuneration corresponds to pay group TV-L 13 with 75% of the weekly working hours for a fixed-term period of 4 years, starting January 1st 2026 the earliest and until at most December 31, 2029 (according to § 2 WissZeitVG) with the aim of obtaining a doctorate.
The project mentoring team also includes: Lars Wörmer (MARUM) and Marcus Elvert (MARUM).
Main Tasks
- Scientific research in the field of:
Microbial biogeochemistry - Developing a new assay for iron reduction rate measurements, microbial community analyses
- Writing of scientific publications
- Participation in ship expeditions
- Participation in international conferences
Formal Requirements:
Completed scientific university degree (Master/University diploma or comparable) in Biochemistry/Microbiology or Biogeochemistry/Geochemistry or related fields.
You are interested?
Please send your application with your complete and informative documents, quoting the reference number A179-25, by 25.07.2025 as a PDF file (max. 5 MB) by unencrypted electronic mail to: office-exc-oceanfloor@uni-bremen.de
or by mail to:
MARUM – Center for Marine Environmental Sciences, University of Bremen
University of Bremen
Prof. Dr. Heiko Pälike
Leobener Street 8
28359 Bremen
Bremen, Germany
Further questions?
Questions about the project can be addressed to Michael Friedrich (michael.friedrich@uni-bremen.de) or Matthias Zabel (mzabel@marum.de).
Notes for Applicants
Please do not enclose any original certificates or references with your application documents. Please note that no photos are to be attached to the application documents. Please also do not use folders or transparencies. Application documents will only be returned on request if you enclose a sufficiently stamped envelope. Personal data is subject to restrictive access control to ensure that only authorized persons can access your data. In principle, your application data will only be used by the responsible application-processing personnel departments of the partner institutions of the cluster. Your application data will not be used for any other purpose or passed on to third parties. By sending us your application documents, we assume that you consent to the collection of your personal data. As soon as your application data is no longer used for the defined purpose of processing your application, it will be deleted immediately in compliance with data protection regulations. If you receive a written rejection, your application documents will be kept until the deadline in accordance with § 15 Allgemeines Gleichbehandlungsgesetz (AGG) has expired and then destroyed. The extent to which costs for the application can be reimbursed must be checked on a case-by-case basis.
Find out more information about this opportunity here.