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Biogeochemistry Group

Congratulations to Jon Graf...
...on the successful defense of his doctoral dissertation on January 18th at the Faculty of Geosciences of the University of Bremen. His doctoral dissertation was entitled:

'Microbial oxidation of methane in stratified freshwater lakes'

Congratulations to one of the pioneers of the Biogeochemistry Group, our technician Kirsten Imhoff...
... on her 25 year anniversary! We are looking forward to the next years.


Research in the Biogeochemistry Group focuses on microbiological and geochemical processes that control bioactive element cycling in the marine environment. We employ geochemical, microbiological, modeling, molecular and single-cell techniques to study the environmental regulation of these processes, and their effects on the global biogeochemical cycles.

Our goal is to provide fundamental insights into microbial mediated processes in the Ocean that ultimately affect Ocean chemistry, biology and climate, and vital input for models used to predict potential future changes resulting from human activities.

Recent news

13. December 2017

New study on N2 fixation

Dinitrogen (N2) fixation is the largest source of new nitrogen (N) to the ocean. The diversity of N2-fixing microorganisms in the ocean is dominated by heterotrophic organisms, yet, very little is known about this particular group. A new study by researchers of the MPI Bremen and the University of Kiel now describes a novel N2-fixing Alphaproteobacterium that was isolated from the oxygen-minimum zone off Peru, a region that has been hypothesized to harbor significant N2 fixation rates. The study gives insights into the metabolic potential and versatility of this newly-isolated N2-fixing microorganism that, based on molecular studies, is potentially widespread in the ocean.

Publication: Metabolic versatility of a novel N2-fixing Alphaproteobacterium isolated from a marine oxygen minimum zone

13. June 2017

New studies on carbon and nitrogen cycling

New studies published online with scientists from the Biogeochemistry Group:

Eichner et al. 

Chemical microenvironments and single-cell carbon and nitrogen uptake in field-collected colonies of Trichodesmium under different pCO2

Marchant et al. (see press release HERE)

Denitrifying community in coastal sediments performs aerobic and anaerobic respiration simultaneously

Oswald, Graf et al. (see press release HERE)

Crenothrix are major methane consumers in stratified lakes

Bristow et al.

Nutrients that limit growth in the ocean

4. April 2017

Gla­cier bac­teri­a’s con­tri­bu­tion to car­bon cyc­ling

A new study published in the journal Nature Geoscience by Dr. Heidi Smith (Montana State University) and colleagues shows how mi­cro­bial com­munit­ies in melt­ing gla­ciers con­trib­ute to the Earth’s car­bon cycle, a find­ing that has global im­plic­a­tions as the bulk of Earth’s gla­ciers shrink in re­sponse to a warm­ing cli­mate. See full MPI press release HERE.

29. March 2017

Phosphorus cycling in the dark ocean

A new study by Dr. Sarah Sokoll and colleagues is coming out in Geophysical Research Letters. This study describes experiments using radiolabeled phosphate that show the rapid uptake of phosphate into particles in sub-euphotic waters off the coasts of Mauritania and Namibia. The experiments and analyses demonstrate that this uptake is biologically mediated, and thus P cycling in the dark ocean is more intense than originally thought. In other words, P associated with sinking organic matter in the ocean is not simply degraded and released into the water column, but cycles several times through a microbial loop. Such intensified P cycling in sinking particles may have implications for the composition of phosphorus bearing organic matter reaching the seafloor, and for global ocean biogeochemical models.

This work was conducted as cooperation between the University Bremen (Marum) and the Max Planck Institute  for Marine Microbiology (MPIMM) in Bremen.

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