Royal Netherlands Institute for Sea Research
Royal Netherlands
Institute for Sea Research

Detecting non-sapropel hypoxic events in the eastern Mediterranean Sea using anaerobic ammonium oxidation biomarkers

The eastern Mediterranean sedimentary record is characterized by the repeated occurrence of black, organic-rich layers called sapropels. These prominent sediments mark episodes of increased productivity and reduced deep-water formation in the eastern Mediterranean Sea as a results of increased freshwater runoff from the African continent. The environmental changes that instigate sapropel formation are largely driven by insolation variability associated to changes in Earth’s precession (i.e., the continuous change in the orientation of Earth's rotational axis). Even though sapropel periods are relatively well-studied events in our geological past, the occurrence of intervals of low-oxygen conditions in between these sapropels are still elusive. Notably, there are episodes where Earth’s precession may have been favorable for sapropel formation but organic-rich sediments have not been found in the eastern Mediterranean Sea. Still, preliminary trace-metal data from eastern Mediterranean sediments suggest that some oxygen depletion may have occurred at these times. Therefore, this MSc project targets to unravel the degree of oxygen depletion during these non-sapropel intervals using organic biomarkers for anaerobic ammonium oxidation (anammox).

Anammox is the oxidation of ammonium using nitrite performed by specific bacteria; a process that only occurs in environments that experience oxygen depletion. Anammox, like denitrification, is important for N removal from the marine system and thus a process essential to understand nutrient cycling. As anammox starts in environments that contain approximately <10 μmol/L O2, the detection of this process also provides information on the oxygenation state of a marine system. As such, we want to use well-preserved organic biomarkers for anammox (i.e., the bacteriohopanetetrol (BHT) isomer and ladderane fatty acids) to pinpoint time intervals with hypoxic but not anoxic conditions in eastern Mediterranean Sea, focusing on sediments that contain ~200.000 years of time. Studying these intervals is essential to expose which environmental boundary conditions drive sapropel formation and thus also marine anoxia in general.


An example of a typical sapropel sediment. Can you find it?

Is this something you would like to do? Contact us! Within the project you will do both lab work (with a focus on organic geochemistry) and data analysis and you will get acquainted will all the basic knowledge to set-up and execute a sound paleo-climatic/-oceanographic research.

MSc student

We’re looking for motivated MSc students with great interest in (past) climate and (organic) geochemistry to conduct this challenging project. The goal is to publish the results from this project in one or several peer-reviewed journal(s), and we aim for students that are willing to be (co-)author. You will be based at NIOZ Royal Netherlands Institute for Sea Research on Texel, with many other students, doing research at an excellent research institute.

Further information

  • Period: approximately 6 months (time interval can be discussed; project goals will be set accordingly)
  • Start date: Summer 2019
  • Contact: Darci Rush, Rick Hennekam and/or Gert-Jan Reichart


Prof. dr. Gert-Jan Reichart

Dr. Darci Rush

Dr. Rick Hennekam