Sequential extraction of P components (SEDEX) in sediment core M157_14-17, off Namibia

A 5-step sequential extraction scheme modified after Ruttenberg (1992), Schenau and De Lange (2000) and Küster-Heins et al., (2010) was used for the speciation of particulate P. Approximately 125mg freeze-dried sediment sample was successively washed with 25 ml of (1) 2 M NH4Cl (pH 7; 4 h; repeat 8 to 10 times), (2) CDB (citrate-dithionite-bicarbonate) buffer solution (pH 7.5; 8 h), (3) 1M sodium acetate buffer solution (pH 4; 6 h), (4) 1 M HCl (24 h) and (5) 1 M HCl (24 h) after ignition for 3 hours at 550 °C. The extracted P components include biogenic P in fish scales, bones and teeth that are mainly composed of hydroxyapatite (PHydap) from step 1, iron-bound P (PFe) from step 2, authigenic apatite (PAuthigenic) from step 3 typically corresponding to carbonate fluorapatite, detrital P (PDetrital) from step 4 and organic P (Porg) from step 5. The sum of these fractions gives the total P content (Ptotal). The P concentration of the solutions was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) with a precision of < 5 %.