title: Are iron-phosphate minerals a sink for phosphorus in anoxic Black Sea sediments?
abstract: Phosphorus (P) is a key nutrient for marine organisms. The only long-term removal pathway for P in the marine realm is burial in sediments. Iron (Fe) bound P accounts for a significant proportion of this burial at the global scale. In sediments underlying anoxic bottom waters, burial of Fe-bound P is generally assumed to be negligible because of reductive dissolution of Fe(III) (oxyhydr)oxides and release of the associated P. However, recent work suggests that Fe-bound P is an important burial phase in euxinic (i.e. anoxic and sulfidic) basin sediments in the Baltic Sea. In this study, we investigate the role of Fe-bound P as a potential sink for P in Black Sea sediments overlain by oxic and euxinic bottom waters. Sequential P extractions performed on sediments from six multicores along two shelf-to-basin transects provide evidence for the burial of Fe-bound P at all sites, including those in the euxinic deep basin. In the latter sediments, Fe-bound P accounts for more than 20% of the total sedimentary P pool. We suggest that this P is present in the form of reduced Fe-P minerals. We hypothesize that these minerals may be formed as inclusions in sulfur-disproportionating Deltaproteobacteria. Further research is required to elucidate the exact mineral form and formation mechanism of this P burial phase, as well as its role as a sink for P in sulfide-rich marine sediments.
authors.affiliation: Department of Earth Sciences - Geochemistry, Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands.
authors.forename: Nikki
authors.initials: N
authors.lastname: Dijkstra
authors.affiliation: Department of Earth Sciences - Geochemistry, Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands.
authors.forename: Peter
authors.initials: P
authors.lastname: Kraal
authors.affiliation: Department of Biogeochemistry, Max Planck Institute for Marine Microbiology, Bremen, Germany.
authors.forename: Marcel M M
authors.initials: MM
authors.lastname: Kuypers
authors.affiliation: Microbiogeochemistry, Institute for Chemistry and Biology of the Marine Environment (ICBM), University of Oldenburg, Oldenburg, Germany.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Schnetger
authors.affiliation: Department of Earth Sciences - Geochemistry, Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands.
authors.forename: Caroline P
authors.initials: CP
authors.lastname: Slomp
mesh_terms: D059038:Black Sea; D020564:Deltaproteobacteria / Q000502:physiology*; D058085:Iron Compounds / Q000737:chemistry* / Q000378:metabolism; D008903:Minerals / Q000737:chemistry* / Q000378:metabolism; D010710:Phosphates / Q000737:chemistry* / Q000378:metabolism; D013440:Sulfides / Q000737:chemistry / Q000378:metabolism; D014871:Water Microbiology
chemical_list: D058085:Iron Compounds; D008903:Minerals; D010710:Phosphates; D013440:Sulfides