Trace elements in the interstitial waters of marine sediments

Abstract

Phosphate and eleven elements were determined in the interstitial waters of four piston cores from the continental borderland area off the coast of Southern California. Calcium, magnesium, potassium, sodium and strontium were determined directly by atomic absorption spectrophotometry. Phosphate was determined colorimetrically and the trace elements: cadmium, cobalt, copper, iron, nickel and zinc, were determined by extraction of the chelate complexes with ammonium pyrollidine dithiocarbamate into methylisobutyl ketone and subsequent analysis by atomic absorption spectrophotometry. Correlation coefficients for various pairs of variables are given. Decrease of Eh and increase of phosphate with depth was attributed mainly to bacterial activity and in the case of phosphate, partly due to release from metal phosphates. Calcium and strontium showed decreases with depth probably due partly to precipitation of carbonate by excess bicarbonate ions produced as a result of bacterial activity and partly to precipitation as phosphate. Potassium levels were higher and magnesium values were slightly lower than in sea water, probably due to interaction with the solid phase of the sediments. Copper showed no overall trends, but zinc showed moderate decrease with depth and correlated well with cadmium. Enrichment of cobalt, zinc, cadmium and copper at the surface of the sediments was attributed to biological concentration, and release, since there is more than sufficient organic matter present to account for such a source. Iron and nickel concentrations were greater in reducing sediments and showed an overall trend to increase with depth.