The long-term sequestration of carbon in the deep ocean depends on the selective preservation of organic compounds during microbial degradation of sinking particulate organic matter (POM). However, the molecular mechanisms and environmental drivers that control the transformation, degradation, and preservation of organic matter in sinking aggregates remain poorly understood. This project will address this gap by 1) identifying which classes of organic molecules are selectively degraded or preserved during microbial processing of sinking aggregates and their role in long-term carbon storage, 2) assessing how sequential microbial colonization by different microbial taxa shape degradation dynamics, element fluxes, and changes in organic matter composition, and 3) quantifying how environmental gradients, including temperature, salinity, nutrient availability, and microbial community structure, affect aggregate transformation during simulated 40-day descent through the water column. The research combines in situ observations with advanced laboratory experiments and high-resolution molecular analyses, including FT-ICR-MS, GC-MS, LC-MS, and single-aggregate sequencing. Respiration and settling velocities will be directly measured under varying environmental conditions. This project builds on analytical pipelines developed during Phase I to track how microbial degradation alters the stoichiometry, lipid, protein, and polysaccharide content, as well as the 3D structure of organic aggregates. By linking molecular-scale changes to microbial activity and environmental context, this work will advance the mechanistic understanding of the biological carbon pump and its efficiency. Ultimately, it will improve our ability to predict the fate of organic carbon in the mesopelagic ocean and its role in climate regulation.
Further Reading
- Arandia-Gorostidi N., Berthelot H., Calabrese F., Stryhanyuk H., Klawonn I., Iversen M. H., Nahar N., Grossart H.-P., Ploug H, Musat N. (2022). Efficient carbon and nitrogen transfer from marine diatom aggregates to colonizing bacterial groups. Scientific Reports, 12(1), 14949, doi: 10.1038/s41598-022-18915-0
- Iversen M. H. (2023) Carbon Export in the Ocean: A Biologist’s Perspective. Annual Review of Marine Science, 15: 357-381, doi: 10.1146/annurev-marine-023122-035153
- Schubotz F. (2024) Going deep on marine lipid metabolism. Science, 385, 1167-1168. doi: 10.1126/science.ads0919
Modalities
The doctoral project will be supervised by Morten Iversen (AWI) and Florence Schubotz (University of Bremen). Depending on the personal expertise of the doctoral candidate, it will be supervised within the working group “Polar Biological Oceanography” (Bremerhaven) or the working group “Organic Geochemistry” (Bremen). The remuneration corresponds to pay group TVöD 13 with 75% of the weekly working hours if based at AWI or pay group TV-L 13 with 75% of the weekly working hours if based at the University of Bremen. The position is 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: Murat Eren (HIFMB) and Sarahi Garcia (UOL).
Main Tasks
- Scientific research in the field of:
Marine Organic Geochemistry / Marine Biogeochemistry / Marine Microbiology - Analysis of:
Organic Export Flux / Biogeochemical Analyses / Mass Spectrometry Imaging / Molecular Sequencing / Experimental Design / Oceanographic data / Long-term Observations - Writing of scientific publications
- Participation in ship expeditions
- Participation in international conferences
Formal Requirements:
Completed scientific university degree (Master/University diploma or comparable) in Marine Geosciences, Biological Oceanography, Chemical Oceanography, Earth Sciences, Marine Microbiology, Environmental Sciences, or a related discipline.
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 Morten Iversen (morten.iversen@awi.de) or Florence Schubotz (fschubotz@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.