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.
September 2015 | "Fe Vici" cruise to the Black Sea with r/v Pelagia, along a gradient from the oxic shelf to the sulfidic deep basin
September 2014 | Short cruise with r/v Mare Nigrum to the deep northwestern Black Sea to collect sediment traps
June 2013 | "PhOxy" cruise to the Black Sea, 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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Kraal, P., Jansen, B., Nierop, K.G., Verstraten, J.M., 2006. Copper complexation by tannic acid in aqueous solution. Chemosphere, 65(11): 2193-8.