Vertical distribution of phosphorus species and iron in sediment at open sea stations in the middle Adriatic region

Sedimentary phosphorus species concentrations were examined in cores (0-10 cm) from 5 locations in the open middle Adriatic in June 2002. Measurements included organic phosphorus (OP) and inorganic P species: P in biogenic apatite (P-FD), P adsorbed onto iron-oxy/hydroxides (P-Fe), P in authigenic apatite (P-AUT) and P in detrital apatite (P-DeT). Total iron (Fe-TOT) and iron-oxyhydroxides (Fe(III)OOH) concentrations were also determined as well as granulometric composition, organic matter (OM), organic carbon (C-ORG) and carbonate content (CA). Sediment pore water measurements included redox-potential (eH) and orthophosphate concentration. All relevant data were subjected to correlation, Cluster and Principal Component Analysis (PCA). Cluster analysis indicated that granulometric composition and carbonate content are the leading factors of distinction between the stations. PCA revealed that the fine fraction of sediments has a key role in the vertical distribution of Fe-TOT and P-ORG. Linkage among P-AUT, P-DeT and C-ORG results from river input influence, while association between OM, P-Fe, eH and OP arises from complex internal processes in the sedimentary P cycle.