A COMPARISON OF THE SCAVENGING OF PHOSPHORUS AND ARSENIC FROM SEAWATER BY HYDROTHERMAL IRON OXYHYDROXIDES IN THE ATLANTIC AND PACIFIC OCEANS

Studies of hydrothermal plumes on the Juan de Fuca Ridge and the Mid-Atlantic Ridge indicate that newly-formed Fe oxyhydroxides, formed as a consequence of hydrothermal venting, readily scavenge P and As from seawater in proportion to the dissolved concentrations of these elements. The Fe content of the suspended matter decreases from approximately 40% near the vents to < 5% in ambient seawater, with particulate P and As concentrations correlating well with Fe throughout this range. The P/Fe ratio in the oxyhydroxide phase is about 1.8 times higher in Juan de Fuca Ridge samples relative to samples from the Mid-Atlantic Ridge. In contrast, the As/Fe ratio in the oxyhydroxide phase is about the same for both regions. Calculated distribution coefficients for P and As in the Fe oxyhydroxide phase show remarkable agreement between the Atlantic and Pacific Oceans. Thus, inter-ocean variations in the element/Fe ratios are a function of dissolved concentrations of the chemical species.