The effect of hydrothermal processes on midwater phosphorus distributions in the northeast Pacific

Abstract

The distributions of dissolved, particulate and sedimentary phosphorus were measured in the region of the Juan de Fuca Ridge to determine the impacts of hydrothermal processes on the phosphorus cycle in the oceans. Significant negative dissolved phosphate anomalies, ranging from 0 to 60 nmol/l, were observed in the water column at depths between 1900 and 2300 db. The largest anomalies ( < −50 nmol/l) were observed within the ridge axis. Corresponding positive particulate phosphorus anomalies and high concentrations of sedimentary phosphorus were also observed to have striking concentration gradients increasing towards the ridge axis. These observations provide strong evidence that phosphorus is being stripped from solution by scavenging reactions. Analysis of the particulate samples employing transmission electron microscopy techniques indicates that the scavenging occurs on newly-formed iron oxyhydroxides of hydrothermal origin. Mass balance calculations suggest that up to 12% of the total annual phosphorus sink in the oceans is a result of scavenging by hydrothermal emissions.