Numerical simulation of hydrothermal vent‐induced circulation at Endeavour Ridge

Abstract

[1] Hydrothermal venting at Endeavour Ridge is focused at five major vent fields spaced at $2-km intervals along a narrow ($1 km wide) north-south trending rift-valley. A Princeton Ocean Model with an axially symmetric rift-valley centered within a rotating, full-depth (2400 m) stratified ocean is used to simulate the circulation and associated temperature and salinity fields generated by vertical heat fluxes from the five vent fields. Steady seafloor heat fluxes are introduced instantaneously to a quiescent ocean using the model provision for boundary fluxes. The model achieves a quasi-steady state in about 80 days. Results are consistent with observation. In particular, buoyant plumes emanating from the larger vent fields rise to ''trapping'' depths as shallow as 1850 m ($350 m above bottom) and spread laterally with the vent-induced circulation. Plume anomalies remain confined to within several kilometers of the ridge, except to the west where anomalies extend more than 10 km off-axis. As with observations, modeled currents within the valley consist of a strong ($10 cm s À1 ) poleward inflow within roughly 75 m of the bottom and an equally strong equatorward counterflow above that depth. Weak ($1 cm s À1 ) equatorward flow develops over the flank of the west ridge and weak poleward flow over the flank of the east ridge. Cyclonic relative vorticity dominates the model circulation within the valley while anticyclonic vorticity prevails above the depth of neutral plume buoyancy. Findings support the notion that turbulent entrainment by buoyant plumes forces a mean poleward flow within the confines of the Endeavour Ridge axial valley.

Deep sea hydrothermal plumes and their interaction with oscillatory flows

“…At the southern and central parts of the valley, the residual flow is predominantly northward and strongest (5 cm/s) while at the northern part of the valley, the residual flow becomes southward and weakest (1 cm/s). The convergent flow within the axial valley is believed to be induced by turbulent entrainment of the hydrothermal plumes [ Thomson et al , 2003, 2005]. The northward residual flow extends to the central valley due to the shallow topographic saddle at the northern end of the valley and more intensive hydrothermal activity within the southern and central valley [ Thomson et al , 2003].…”

The importance of hydrothermal venting to water-column secondary production in the northeast Pacific

“…In addition, the different attributes and chemistry of individual vent plumes have differing effects on the biomass distributions over the 15 km length of the axial valley (Kelley et al, 2012;Lavelle et al, 2013). Variations in the tidal and non-tidal (residual) currents also affect the drift of the plumes, which are especially variable over the ridge where topographic factors are most pronounced (Thomson et al, , 2005). Spatial and temporal variations in the plumes are also expected to affect the distribution of opportunistic epiplume organisms in the deep scattering layer overlying the vent fields.…”

“…These variations also contribute to considerable temporal variability in the depths and horizontal positions of the deep scattering layers (Burd and Thomson, 2012). Currents within the axial valley are constrained in the along-axis direction and are strongly sheared in the horizontal directions due to the effects of the ridge topography and venting-induced flows (Thomson et al, 2003(Thomson et al, , 2005Lavelle et al, 2013). Deep circulation above the axial ridge is generally to the west, as shown by the presence of vent-plume signatures found 410 km to the west of the ridge axis (Burd and Thomson, 1994).…”

“…In June and July of 1991-1996, we collected 197 net samples from 33 tows undertaken at various hours of the day within 200 km of four of the five primary identified Endeavour Ridge vent fields (Salty Dawg, High Rise, Main Endeavour and Mothra) located at 2200 m depth at 47157ʹ N, 129106ʹ W in the northeast Pacific (Thomson et al, 2005). Fig.…”

“…Our estimate for the "distance from the vents" corresponds to the mean lateral distance in kilometers from the up-cast portion of a given tow to the four main vent fields in the axial valley (Thomson et al, 2005). One of the tows was from the Explorer Ridge venting region (Tunnicliffe et al, 1986) located roughly 80 km to the northeast of Endeavour Ridge, and two tows were from the Coaxial Seamount region (Baker et al, 1995;Tunnicliffe et al, 1997) located 125 km to the south of Endeavour Ridge.…”