The Leibniz Centre for Tropical Marine Research (ZMT) in Bremen is a member of the Leibniz Association, which is supported by the German Federal and State Governments. Through its research, ZMT contributes to developing strategies for sustainable use of tropical coastal systems.

The Systems Ecology Group is looking for a

Doctoral candidate (gn)

(Reference number: 225-N2FIX)

Modelling N2-fixation in the global ocean (N2FIX): Understanding of the role of tropical regions in the global nitrogen cycle

Supervisors: Subhendu Chakraborty & Agostino Merico

Nitrogen is an essential element for all living organisms but its availability often limits the growth and productivity of terrestrial and aquatic ecosystems. Although molecular nitrogen (N2) is highly abundant both in the atmosphere and the sea, only specific and highly specialized micro-organisms can convert N2 into a biologically usable form of nitrogen. Such conversion (known as N2 fixation) impacts on primary production and affects the global biogeochemical cycles of both nitrogen and carbon, with relevant implications for the global climate.

N2 fixation is believed to be restricted within the sunlit layers of tropical and subtropical oceans. Recent observations reveal that N2 fixing organisms are geographically widespread and affect primary production in many parts of the global ocean. However, the environmental and ecological factors that leads to latitudinal variations in the distribution of different N2 fixing organisms are largely unknown.

In this project, the Ph.D. student will either modify an existing mathematical model for unicellular N2 fixing bacteria or develop a new model. The model will be appropriately engineered for studying the effects of different environmental conditions on organisms and their N2 fixing abilities. The model will be used in combination with different observational data to (1) understand the ecological mechanisms driving the competition of N2-fixing organisms, (2) investigate how environmental conditions affect N2 fixation rates ins different organisms, and (3) disentangle the contributions of tropical and temperate regions to the global nitrogen budget.


Applicants must hold a Master degree in one of the following disciplines: applied mathematics, physics, computational sciences, marine biogeochemistry, physical oceanography, environmental sciences, theoretical ecology, or in similar quantitative or numerical disciplines. Furthermore, candidates should have good programming skills and a keen interest in biogeochemical processes of global scale relevance. We are looking for highly motivated students with good communication and scientific writing skills. A good level of written and oral English is required. This PhD project is part of a cooperation between the Systems Ecology Group (Dr. Subhendu Chakraborty & Prof. Agostino Merico) and the Centre for Ocean Life of the Technical University of Denmark (Prof. Ken Andersen) and thus travels to Copenhagen to discuss progress with our partner are expected.

Please contact Prof. Dr. Agostino Merico ( or Dr. Subhendu Chakraborty ( for further information.

We offer:

  • An exciting working environment in an interdisciplinary and internationally oriented institute
  • A highly motivated, solution oriented and inspiring group of colleagues
  • Embedding in a large consortium within the German Marine Science landscape
  • A family-friendly diverse working environment

The position should be filled from June 1st 2022. The contract will be limited to 36 months. Salary will be paid according to the German TV-L EG 13 (2/3 of a fulltime position).

ZMT is an equal opportunity employer. The ZMT values its diverse workforce and pursues the goal of providing equal opportunity, which incorporates gender neutrality (gn). Applicants with a migration background are welcome. Disabled persons with comparable qualification receive preferential status.

Please send your application (which should include CV and motivation letter specifying your interests in the topic of the position) by March 30th, 2022 as a single pdf file with the reference number "225- N2FIX" to Ms. Lena Oehlmann, E-Mail: Note, however, that applications will be considered also after the deadline if a suitable candidate is not found by that date.

We will be happy to accept your documents without a photo.

Leibniz Centre for Tropical Marine Research, Fahrenheitstraße 6, D-28359 Bremen.

posted: 28 September 2021     Please mention EARTHWORKS when responding to this advertisement.