VERTICAL AND TEMPORAL VORTICITY OBSERVATIONS AT JUAN-DE-FUCA RIDGE - HYDROTHERMAL SIGNATURES

Moored current measurements made from April 1994 to June 1995 reveal t he vertical and temporal structure of the vorticity over the northern segment of the Juan de Fuca Ridge. At a depth of 2100m, near the therm al and particle maximum associated with the neutrally buoyant hydrothe rmal plume, the relative vorticity is anticyclonic with a mean value o f nearly -0.09f, with variability of the same magnitude. This arises f rom cross-ridge shear in the horizontal currents at this level. In the vertical, the anticyclonic shear has a peak value at plume level decr easing in magnitude both upward and downward from depths of 2100-2150m . As the bottom is approached, the transverse shear changes sign with cyclonic values of up to 0.09f below 2250m depth. This vorticity signa ture is suggestive of dynamics of a line source of buoyant fluid enter ing the plume at its neutral density horizon and not due to individual point sources.