PhD position EXC1-01 Carbon Sequestration at the Molecular Level – Deadline 25 July 2025

Project Description

The overarching goal of this project is to identify carbon-sequestration mechanisms on a molecular level within the ocean and its sediments. Freshly produced organic matter derived from marine phytoplankton and terrestrial higher plants is largely composed of biomolecules of known building blocks, such as polysaccharides, lignin, proteins, lipids and nucleic acids. But these represent only a minute fraction of the millions of compounds constituting deep-sea dissolved organic matter (DOM) and sediment organic matter (SOM). The pioneering geochemist John Hedges stated, “the future of oceanographic research belongs in large part to those who can learn to read these molecular messages.”. This insight remains prescient, because current analytical methods resolve only a small subset of marine OM, impeding the establishment of structure–function relationships essential for understanding OM storage and turnover.

Long-term preservation of SOM may hinge on specific structural motifs, whereas DOM persistence could emerge from ecosystem-level processes rather than intrinsic molecular stability. In the water column, particles constitute hotspots for microbial OM degradation. In sediments, however, particle and pore-space heterogeneity may enhance stabilization. Here, we will follow organic particles and DOM from their formation in productive surface waters, through the water column into oxic and anoxic sediment layers where thermodynamic constraints prevail. To overcome analytical limitations, we will implement a multi-modal analytical framework, combining various high-resolution mass spectrometry techniques and high-field nuclear magnetic resonance spectroscopy with advanced chemometric appraoches. In collaboration with cluster partners, OM fractions will be radiocarbon-dated and microbial communities will be profiled via integrated multi-omics approaches. By linking molecular signatures to microbial functions across environmental gradients, this integrated strategy will “read” the molecular messages of the marine carbon cycle and yield a mechanistic understanding of oceanic carbon sequestration.

Further Reading

• Hedges J (2002) Why dissolved organics matter. In: Hansell DA, Carlson CA, editors. Biogeochemistry of Marine Dissolved Organic Matter (1st ed), Academic Press. p. 1-33. doi:10.1016/B978-012323841-2/50003-8  .
• Dittmar T, Lennartz ST, Buck-Wiese H, Hansell DA (…) & Hehemann JH (2021) Enigmatic persistence of dissolved organic matter in the ocean. Nat Rev Earth Environ 2, 570-583. doi:10.1038/s43017-021-00183-7  .
• Dittmar T & Lennartz ST (2024) Reasons behind the long-term stability of dissolved organic matter, in: Hansell DA & Carlson CA (Eds.), Biogeochemistry of marine dissolved organic matter (3rd Ed.). Academic Press, pp. 613-655. doi:10.1016/B978-0-443-13858-4.00006-X  .
• Liu W, Holm HC, Lipp JS, Fredricks HF, Van Mooy BA, Hinrichs KU (2025) Unraveling plankton adaptation in global oceans through the untargeted analysis of lipidomes. Sci Adv 11, eads4605 (2025). doi:10.1126/sciadv.ads4605 
• LaRowe DE, Arndt S, Bradley JA, Estes ER (…) & Zhao R (2020) The fate of organic carbon in marine sediments – New insights from recent data and analysis. Earth-Sci Rev 204. doi:10.1016/j.earscirev.2020.103146  .

Modalities

The doctoral project will be supervised by Thorsten Dittmar (University of Oldenburg) and Kai-Uwe Hinrichs (University of Bremen). Depending on the personal expertise of the doctoral candidate, the project will be supervised within the working group “Marine Geochemistry” (Oldenburg) or the working group “Organic Geochemistry” (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: Gesine Mollenhauer (AWI) and Sarahi Garcia (UOL).

Main Tasks

• Scientific research in the field of:
  Marine Biogeochemistry / Organic Geochemistry / Organic carbon preservation
• Analysis of:
  Molecular composition of sinking particles and sediments and associated dissolved organic matter with help of ultrahigh-resolution mass spectroscopy and high-field nuclear magnetic resonance spectroscopy
• 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 Environmental Sciences, Geochemistry, Geoecology, Analytical Chemistry, Biochemistry or related fields with a focus on organic geochemistry or analytical chemistry.

Further questions?

Questions about the project can be addressed to Thorsten Dittmar (thorsten.dittmar@uol.de) or Kai-Uwe Hinrichs (khinrichs@uni-bremen.de).