Middepth flow near hydrothermal venting sites on the southern Juan de Fuca Ridge

Abstract

Long-term moored current measurements around the southern end of the Juan de Fuca Ridge show that flow parallels the ridge and may be intensified by its presence. The mean flow is northward on the west side and southward on the east. Thus plumes emanating from the ridge probably are advected along the ridge before flowing away from the ridge. Other topographic features may be responsible for westward or eastward turning. Along the west side of the ridge, we hypothesize a regional flow pattern with southward flow north of Axial Seamount, northward flow south of Axial, and a convergence somewhere south of Axial resulting in westward flow. Along the east side, the flow may be southward everywhere. Above the ridge crest the long-term mean flow is weaker and more variable, and it includes tidal, inertial, and a dominant broadband 4-day oscillation. This 4-day energy is maximum in the rift valley (where the inertial is least), decreases upward and away from the ridge, and is more energetic in winter. This oscillation is predominately a clockwise rotating feature which, along with the presence of inertial oscillations, suggests that it may be storm-induced from the sea surface. These observations along with those by Cannon and Pashinski (1990) suggest northward propagation. Flow variations across the ridge lasting one to a few months have mean speeds of 1-3 cm/s and are capable of transporting plumes off axis to the west or east into the northerly or southerly flows, respectively. 12,815

Hydrography and circulation near the crest of the East Pacific Rise between 9° and 10°N

“…The LADDER observations and model simulations of anticyclonically sheared along-flank boundary currents near the EPR crest are remarkably similar to observations from the Juan de Fuca Ridge near 45 • N (Cannon et al, 1991;Cannon and Pashinski, 1997;Helfrich et al, 1998). In that region, too, there are anticyclonically sheared boundary currents associated with mean speeds of several cm·s −1 a few km from the ridge crest and limited to off-axial distances of less than 25 km (Cannon and Pashinski, 1997).…”

Exploring the Ecology of Deep-Sea Hydrothermal Vents in a Metacommunity Framework

“…Because of horizontal and vertical shear associated with these ridge-crest boundary currents, dispersal depends on larval vertical positioning and the direction of the instantaneous flow at the time of larval release (Jackson et al, 2010). Similar ridge-crest boundary currents affecting regional dispersal have been observed in the northeastern Pacific along the Juan de Fuca Ridge (Cannon et al, 1991;Cannon and Pashinski, 1997;Helfrich et al, 1998). Characterized by an intermediate spreading rate, this ridge has a relatively shallow median valley.…”

Buoyancy‐driven plumes in rotating, stratified cross flows: Plume dependence on rotation, turbulent mixing, and cross‐flow strength

“…along the strike of ridge crests show that plumes from chronic sources can extend longitudinally for many tens of kilometers, as plumes from separate sources coalesce in background currents, which are often along ridge [Cannon et al, 1991 ]. The model in this paper is intended to address features of a plume from a single, somewhat broad chronic discharge site, e.g., a sulfide mound.…”