Mean hydrographic and velocity sections near Pipe Organ Vent at Juan de Fuca Ridge

Abstract

A composite cross‐ridge hydrographic and velocity section near the Pipe Organ vent site on the Juan de Fuca Ridge is presented. The hydrographic section is composed of surveys obtained from 1990 to 1994. The potential temperature field shows pronounced downward sloping of the isotherms below 1.9° (centered at about 150 m above the bottom) on either side of the ridge crest. The horizontal scale is about 2 km, comparable to the local Rossby deformation radius. The maximum potential temperature anomaly is greater than 0.03°C. Significant light attenuation anomalies are also present. The mean along‐ridge velocity section is constructed from the records of 85 current meters. The mean flow is southward at and to the east of the vent and northward to the west. Largest velocities occur at the depth of the neutrally buoyant plume. The cross‐ridge shear is thus anti‐cyclonic with a characteristic value of −0.05f. Geostrophic velocity fields obtained from the density section differ significantly from the field produced from the current meter data. An estimate of the net mean flux of anomalous heat gives 780 (±400) MW to the south.