The Ocean Floor

Molecular Gatekeepers of Carbon Sequestration: Selective Preservation and Microbial Degradation in Sinking Marine Aggregates

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Project Description

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.

Further questions?

Questions about the project can be addressed to Morten Iversen ([Bitte aktivieren Sie Javascript]) or Florence Schubotz ([Bitte aktivieren Sie Javascript]).