Plain English Summary
Marine geochemist Peter Kraal studies the dynamics of essential nutrients in the oceans. ‘My favourite is P: phosphorus. That is a particularly relevant nutrient, because we are rapidly exhausting the available supplies of phosphorous in the world for agriculture. Ultimately, this phosphorus is discharged into the seas and oceans, where it can cause huge environmental problems.’
‘Phosphorus can give such a strong boost to algal growth that subsequently all oxygen in the seawater is consumed during the breakdown of all those dead, rotting algae. Under such oxygen-free conditions, phosphorus is not absorbed as efficiently into the seafloor and “old” phosphorus is even released as a nutrient to further promote algal growth. This is a vicious circle, which led to prolonged periods of oxygen loss in the past. It is still noticeable in coastal seas, such as the Baltic Sea, where the enormous growth of harmful algae still continues even when the worst supply of phosphorous from agriculture to the surface water is limited.’
‘The bonding of phosphorus to iron molecules is one of the keys in my research. In nature, this bonding has a significant influence on the amount of phosphorus that is available. Bonding to iron therefore regulates the algal growth. Iron minerals are also often used in (waste)water purification to remove unwanted substances such as phosphorus. The reuse of this phosphorus as a fertiliser in agriculture is an important link in “repairing” the phosphorus cycle.’
‘I am currently focusing on the bonding of phosphorous to limestone (calcium carbonate). As a result of acidification, limestone dissolves and less phosphorus is bonded. We do not yet understand the consequences of this at all. With my research, I hope to make a contribution to a better understanding of the nutrient cycles in the oceans and therefore to solving environmental problems, such as oxygen-free coastal seas.’Read more +
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.
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
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).