Royal Netherlands Institute for Sea Research
Royal Netherlands
Institute for Sea Research
Phone number
+31 (0)222 369 455
Ocean Systems (OCS)
Tenure track Scientist
  • Marine (bio)geochemistry
  • Nutrient cycling and redox chemistry
  • Past and present ocean deoxygenation
  • Micro-scale element and mineral characterization
  • Sampling under oxygen-free conditions

Dr. Peter Kraal

Tenure track Scientist

Research Interests

I am a marine geochemist investigating the interplay between oxygen availability and the biogeochemical cycling of essential elements such as iron and phosphorus in marine waters and sediments. Globally increasing eutrophication and marine oxygen depletion, often caused or exacerbated by human activities, gets me worried but also scientifically excited.

Moreover, I have developed a strong interest in analytical techniques that push our understanding of this research field forward, such as X-ray absorption spectroscopy for particle characterization and polymer-based passive sampling techniques for high-resolution, two-dimensional porewater analysis.

To understand past and future impacts of marine deoxygenation I investigate the mineralogy, chemical composition and fluxes in modern surface sediments as well as the chemical signature of oxygen depletion in historical sediment records. A particular interest of mine is the impact of (changing) chemical conditions on the stability of authigenic minerals.

Sampling sediments from the Black Sea under oxygen-free conditions

Education and Experience

2015 - 2017 NWO-Veni postdoctoral fellow at Utrecht University - Department of Earth Sciences-Geochemistry; Iron mineral transformations and preservation: Effects of eutrophication-driven changes in sediment geochemistry

2013 - 2014 Postdoctoral researcher at Utrecht University - Department of Earth Sciences-Geochemistry; Coupled cycling of iron, phosphorus and manganese in the Black Sea

2011 - 2013 Postdoctoral researcher at Southern Cross University - Geosciences; Hyperaccumulations of monosulfidic sediments: Exploring a biogeochemical extreme to resolve fundamental sulfur biomineralisation pathways

2006  -2010 PhD student at Utrecht University - Department of Earth Sciences-Geochemistry; Redox-dependent phosphorus burial in modern and ancient marine sediments

Research expeditions

I have been involved in various research cruises, during which I collected and processed (anoxic) water column and sediment samples for on-board and on-shore analyses.

February 2019 | Chief scientist on the FUNAMOX (Biogeochemical functioning in Namibian oxygen-depleted waters) expedition with RV Pelagia to the Namibian shelf and slope, sampling water column and sediments to understand the impact of oxygen depletion on the biogeochemical cycling of essential elements such as N, P and trace metals.

July 2018 | Co-chief scientist on NICO Leg 12 to the mid-Atlantic ridge with RV Pelagia to sample waters and sediments around the Rainbow hydrothermal vent field

September 2015 | "Fe Vici" cruise to the Black Sea with RV Pelagia, along a gradient from the oxic shelf to the sulfidic deep basin

September 2014 | Short cruise with RV Mare Nigrum to the deep northwestern Black Sea to collect sediment traps

June 2013 | "PhOxy" cruise to the Black Sea with RV Pelagia, along a gradient from the oxic shelf to the sulfidic deep basin

2011 - 2012 | Various samping trips to the shallow Peel-Harvey Estuary in Western Australia

May/June 2009 | "HYPER" cruise to the Baltic Sea with r/v Aranda to the Baltic Sea

August/September 2007 | Cruise to the Baltic Sea with r/v Skagerrak



Kraal, P., van Genuchten, C.M., Behrends, T., Rose, A.L., 2019. Sorption of phosphate and silicate alters dissolution kinetics of poorly crystalline iron (oxyhydr)oxide. Chemosphere 234, 690-701.

Kraal, P., Yücel, M., Slomp, C.P., 2019. Turbidite deposition and diagenesis in the southwestern Black Sea: Implications for biogeochemical cycling in an anoxic basin. Marine Chemistry, 209: 48-61 (DOI link)

Schoepfer, V.A., Burton, E.D., Johnston, S.G., Kraal, P., 2019. Phosphate loading alters schwertmannite transformation rates and pathways during microbial reduction. Science of The Total Environment, 657: 770-780 (DOI link)

Lenstra, W.K., Hermans, M., Séguret, M.J.M., Witbaard, R., Behrends, T., Dijkstra, N., van Helmond, N.A.G.M., Kraal, P., Laan, P., Rijkenberg, M.J.A., Severmann, S., Teacǎ, A., Slomp, C.P., 2019. The shelf-to-basin iron shuttle in the Black Sea revisited. Chemical Geology, 511: 314-341 (DOI link).

van Genuchten, C.M., Behrends, T., Kraal, P., Stipp, S.L.S., Dideriksen, K., 2018. Controls on the formation of Fe(II,III) (hydr)oxides by Fe(0) electrolysis. Electrochimica Acta, 286: 324-338 (DOI link).

Dijkstra, N., Kraal, P., Séguret, M.J.M., Flores, M.R., Gonzalez, S., Rijkenberg, M.J.A., Slomp, C.P., 2018. Phosphorus dynamics in and below the redoxcline in the Black Sea and implications for phosphorus burial. Geochimica et Cosmochimica Acta, 222(Supplement C): 685-703 (DOI link).

Kraal, P., Dijkstra, N., Behrends, T., Slomp, C.P., 2017. Phosphorus burial in sediments of the sulfidic deep Black Sea: key roles for adsorption by calcium carbonate and apatite authigenesis. Geochimica et Cosmochimica Acta, 204: 140-158 (DOI link).

Schoepfer, V.A., Burton, E.D., Johnston, S.G., Kraal, P., 2017. Phosphate-imposed constraints on schwertmannite stability under reducing conditions. Environmental Science & Technology, 51(17): 9739-9746 (DOI link).

Egger, M., Kraal, P., Jilbert, T., Sulu-Gambari, F., Sapart, C.J., Röckmann, T., Slomp, C.P., 2016. Anaerobic oxidation of methane alters sediment records of sulfur, iron and phosphorus in the Black Sea. Biogeosciences, 13(18): 5333-5355 (DOI link).

Kraal, P., Bostick, B.C., Behrends, T., Reichart, G.-J., Slomp, C.P., 2015a. Characterization of phosphorus species in sediments from the Arabian Sea oxygen minimum zone: Combining sequential extractions and X-ray spectroscopy. Marine Chemistry, 168(0): 1-8 (DOI link).

Kraal, P., Burton, E.D., Rose, A.L., Kocar, B.D., Lockhart, R.S., Grice, K., Bush, R.T., Tan, E., Webb, S.M., 2015b. Sedimentary iron–phosphorus cycling under contrasting redox conditions in a eutrophic estuary. Chemical Geology, 392(0): 19-31 (DOI link).

Chen, A.P., Berounsky, V.M., Chan, M.K., Blackford, M.G., Cady, C., Moskowitz, B.M., Kraal, P., Lima, E.A., Kopp, R.E., Lumpkin, G.R., Weiss, B.P., Hesse, P., Vella, N.G.F., 2014. Magnetic properties of uncultivated magnetotactic bacteria and their contribution to a stratified estuary iron cycle. Nat Commun, 5 (DOI link).

Dijkstra, N., Kraal, P., Kuypers, M.M.M., Schnetger, B., Slomp, C.P., 2014. Are iron-phosphate minerals a sink for phosphorus in anoxic Black Sea sediments? PLoS ONE, 9(7): e101139 (DOI link).

Kraal, P., Slomp, C.P., 2014. Rapid and extensive alteration of phosphorus speciation during oxic storage of wet sediment samples. PLoS ONE, 9(5): e96859 (DOI link).

Burton, E.D., Johnston, S.G., Kraal, P., Bush, R.T., Claff, S., 2013. Sulfate availability drives divergent evolution of arsenic speciation duringmicrobially mediated reductive transformation of schwertmannite. Environmental Science & Technology, 47(5): 2221-2229 (DOI link).

Kraal, P., Burton, E.D., Bush, R.T., 2013a. Iron monosulfide accumulation and pyrite formation in eutrophic estuarine sediments. Geochimica et Cosmochimica Acta, 122(0): 75-88 (DOI link).

Kraal, P., Burton, E.D., Rose, A.L., Cheetham, M.D., Bush, R.T., Sullivan, L.A., 2013b. Decoupling between water column oxygenation and benthic phosphate dynamics in a shallow eutrophic estuary. Environmental Science & Technology, 47: 3114-3121 (DOI link).

Lockhart, R.S., Berwick, L.J., Greenwood, P., Grice, K., Kraal, P., Bush, R., 2013. Analytical pyrolysis for determining the molecular composition of contemporary monosulfidic black ooze. Journal of Analytical and Applied Pyrolysis, 104(0): 640-652 (DOI link).

Kaal, J., Nierop, K.G.J., Kraal, P., Preston, C.M., 2012. A first step towards identification of tannin-derived black carbon: Conventional pyrolysis (Py–GC–MS) and thermally assisted hydrolysis and methylation (THM–GC–MS) of charred condensed tannins. Organic Geochemistry, 47(0): 99-108 (DOI link).

Kraal, P., Slomp, C.P., Reed, D.C., Reichart, G.J., Poulton, S.W., 2012. Sedimentary phosphorus and iron cycling in and below the oxygen minimum zone of the northern Arabian Sea. Biogeosciences, 9(7): 2603-2624 (DOI link).

Kraal, P., Slomp, C.P., de Lange, G.J., 2010a. Sedimentary organic carbon to phosphorus ratios as a redox proxy in Quaternary records from the Mediterranean. Chemical Geology, 277(1-2): 167-177 (DOI link).

Kraal, P., Slomp, C.P., Forster, A., Kuypers, M.M.M., 2010b. Phosphorus cycling from the margin to abyssal depths in the proto-Atlantic during oceanic anoxic event 2. Palaeogeography, Palaeoclimatology, Palaeoecology, 295(1-2): 42-54 (DOI link).

Kraal, P., Nierop, K.G.J., Kaal, J., Tietema, A., 2009a. Carbon respiration and nitrogen dynamics in Corsican pine litter amended with aluminium and tannins. Soil Biology and Biochemistry, 41(11): 2318-2327 (DOI link).

Kraal, P., Slomp, C.P., Forster, A., Kuypers, M.M.M., Sluijs, A., 2009b. Pyrite oxidation during sample storage determines phosphorus fractionation in carbonate-poor anoxic sediments. Geochimica et Cosmochimica Acta, 73(11): 3277-3290 (DOI link).

Kraal, P., Jansen, B., Nierop, K.G., Verstraten, J.M., 2006. Copper complexation by tannic acid in aqueous solution. Chemosphere, 65(11): 2193-8 (DOI link).

Linked news

Thursday 13 February 2020
NWO-grant to investigate dredged harbour sediment as carbon neutral building material
A team of researchers from NIOZ and Utrecht University have won a grant from the NWO Topsector Water & Maritiem to investigate the potential of dredged harbour sediment as a carbon neutral resource for building materials. The team will investigate…

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Tuesday 26 February 2019
NIOZ@SEA | FUNAMOX expedition in the southeast Atlantic
Off the coast of southwest Africa, currents force cold deep waters full of essential elements required for ocean life to the surface. This so-called upwelling has enormous impacts on the chemistry and biology of the water and sediment. We are sailing…

NIOZ publications