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PhD-position: "Oceanic phosphorus fluxes and their sensitivity to anthropogenic environmental change (PHOSFLUX)"

  • 't Horntje, Texel, Noord-Holland, Netherlands
Ocean systems (OCS)

Job description

The department of Ocean Systems (OCS: principal investigator dr. Peter Kraal) at the Royal Netherlands Institute of Sea Research (NIOZ) is looking for a highly motivated PhD student with a background in (bio)geochemistry/chemical oceanography to investigate the impact of ocean acidification on the marine phosphorus cycle. Your research will focus on the North Atlantic Ocean and is part of a fully funded project.


NWO-NIOZ Royal Netherlands Institute for Sea Research is the Dutch national oceanographic institute and principally performs frontier multidisciplinary, fundamental and applied marine research, addressing important scientific and societal questions pertinent to the functioning of the ocean and seas. NIOZ includes the National Marine research Facilities (NMF) department that operates a fleet of research vessels and the national pool of large seagoing equipment, and supports excellence in multidisciplinary marine research, education, and policy development.

The department of Ocean Systems (OCS) studies the role of the ocean in a changing climate, from equator to pole, from the continental shelf to the deep ocean and from the past to the present. The ocean is Earth’s largest reservoir of CO2 and heat; circulation, mixing, biogeochemistry and other marine processes strongly impact global climate. Advanced ocean observations allow us to decipher the current and future functioning of the ocean. Furthermore, seafloor sediments have recorded past changes in conditions on land and in the ocean, in the form of biological residues or physical and chemical signals, which allow us to reconstruct feedbacks between oceanic processes and climate in the (ancient) past. Today, the ocean is changing rapidly because of (human) stressors such as excess CO2, warming and eutrophication. This impacts on the strongly linked but poorly understood ocean processes that control marine ecosystem functioning and thereby climate. The OCS department investigates ocean functioning by means of sea-going expeditions, during which data and samples are collected from the water column and the seafloor. The unique combination of on-board and on-shore experimentation, sample processing and analysis allow us to produce high-quality data and mechanistic insight into ocean functioning and perturbation.


Microscopic calcite (CaCO3) shells of plankton sink through ocean waters to the seafloor by the trillions each year, taking along essential nutrients such as phosphorus (P). Ocean acidification is likely to alter global CaCO3 fluxes, with so far unknown consequences for P cycling, ocean fertility and CO2 uptake. Our lack of knowledge regarding these feedbacks limits our insight in ocean functioning under environmental change, both in the (ancient) past and the human-impacted future. The NWO-funded PHOSFLUX project aims to shed light on these unknowns, by quantifying the role of CaCO3 fluxes and acidification in global marine P cycling through a combination of field work in the North Atlantic Ocean, laboratory experiments and mathematical modelling. A scientific cruise with our research vessel Pelagia will allow us to investigate CaCO3 – P interactions in the field. Through controlled lab experiments, we will dive deeper into the underlying chemical and mineralogical processes, to eventually capture them in physical-chemical models that predict the impact of acidification on marine P cycling. The project is a collaboration between NIOZ and Utrecht University (UU; prof. dr. Mariëtte Wolthers), combining unique sea-going experimentation with advanced analytical tools to understand mineral-water interactions from microscopic to ocean-basin scale.

Within the PHOSFLUX project, you will perform field and laboratory work to gain insight into the uptake and transformation of P by CaCO3. Using the broad array of sea-going equipment at NIOZ, we will investigate interactions between CaCO3 and P as particles sink from the sea surface to extremely (>5-km) deep waters where CaCO3 dissolves. This sea-going research is a key part of your PhD research. Field work at sea is as rewarding as it is challenging: you are flexible and creative, able to deal with setbacks and to seize new opportunities. In the laboratory, you use and optimize setups (reactors) to study CaCO3 – P interactions under variable environmental conditions, also measuring parameters that are subsequently used by the postdoc associated to the overarching project (at UU) to model these interactions. Furthermore, we will apply for analysis time at large-scale research infrastructure for advanced analysis of CaCO3 – P interactions (e.g. synchrotrons, microscopy facilities). PHOSFLUX is a NIOZ-UU collaboration and you are expected to contribute pro-actively to open and effective exchange of ideas and results. You present the data from the field and lab experiments at (international) conferences and you prepare scientific articles for publication in peer-reviewed journals. Within OCS, you share your knowledge and expertise with your colleagues in an open, safe and inclusive environment.

Job requirements


We seek an enthusiastic and energetic candidate who has a keen interest in marine biogeochemistry and who is eager to sail the Atlantic Ocean and endure challenging conditions to get unique field data. You are a team player, with:

  • An MSc degree in earth sciences, oceanography or a related field
  • Experience and affinity with biogeochemistry and marine research
  • Passion for chemical laboratory work and data analysis
  • An open, communicative and collaborative attitude
  • Strong communication skills in English

We want to be a transparent institute with a healthy working climate and an inclusive culture, where people from diverse backgrounds and gender bring their talents and further develop these talents. We aim for inclusive decision-making processes and expect our leadership to show visible commitment, awareness of bias, and cultural intelligence.


  • Employment of this full-time position at Royal NIOZ is by NWO-I, for a total duration of 4 years. You start with an appointment for the duration of 1 year, that, after a positive evaluation in the 9th month (Go-No go), will be extended to the full period of 4 years.
  • Salary compliant with scales for PhD candidate (OIOs) CAO-WVOI (Collective Labour Agreement for Dutch Research Institutes).
  • An appointment at NIOZ as a PhD candidate means working and learning simultaneously conform the NIOZ PhD policy.
  • 338 annualized holiday hours for a full-time 40-hour work week.
  • Pension scheme via ABP, 8% holiday allowance and a year-end bonus of 8.33%.
  • 2nd class public transportation travel is reimbursed 100%.
  • Employment benefits plan to exchange a portion of your salary for days off or vice versa, or can be used to purchase a bicycle with tax benefits.
  • We offer relocation expenses for employees coming from abroad and support with finding accommodation.


Field work for the project is planned for spring 2025, the PhD is currently planned to start fall 2024, with some flexibility. For additional information about this vacancy, please contact Peter Kraal ( For additional information about the procedure, please send an e-mail to

Closing date for this vacancy is the 25th of August. We aim to invite suitable candidates for an interview on the 25th of September.