Variations in mean currents affecting hydrothermal plumes on the Juan de Fuca Ridge

Cannon, G. A.; Pashinski, David J.

doi:10.1029/97jc01910

Cited by 36 publications

(35 citation statements)

References 17 publications

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“…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).…”

Section: Discussionsupporting

confidence: 60%

“…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). While the claim of Helfrich et al (1998) that the along-ridge flows are strongest at the depth of the regional neutrally buoyant hydrothermal plumes is apparently inconsistent with the LADDER observations and model results it is noted that the current meters used by Helfrich et al (1998) neither sampled the velocities over the ridge flanks below crest level (where the velocities in the boundary currents on the EPR are largest) nor laterally bracketed the velocity maxima on the ridge flanks (their Fig.…”

Section: Discussionmentioning

confidence: 99%

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

Thurnherr

Ledwell

Lavelle

et al. 2011

Deep Sea Research Part I: Oceanographic Research Papers

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1ABSTRACT. Topography has a strong effect on the physical oceanography over the flanks and crests of the global mid-ocean ridge system. Here, we present an analysis of the hydrography and circulation near the crest of the East Pacific Rise (EPR) between 9 • and 10 • N, which coincides with an integrated study site (ISS) of the RIDGE2000 program. The analysis is based primarily on survey and mooring data collected during the LADDER project, which aimed to investigate oceanographic and topographic influences on larval retention and dispersal in hydrothermal vent communities. Results indicate that the yearly averaged regional mean circulation is characterized by a westward drift of 0.5-1 cm·s −1 across the EPR axis and by north-and southward flows along the western and eastern upper ridge flanks, respectively. The westward drift is part of a basin-scale zonal flow that extends across most of the Pacific ocean near 10 • N, whereas the meridional currents near the ridge crest are a topographic effect. In spite of considerable mesoscale variability, which dominates the regional circulation and dispersal on weekly to monthly time scales, quasi-synoptic surveys carried out during the mooring deployment and recovery cruises indicate subinertial circulations that are qualitatively similar to the yearly averaged flow but associated with significantly stronger velocities. Weekly averaged mooring data indicate that the anticyclonically sheared along-flank flows are associated with core speeds as high as 10 cm·s −1 and extend ≈10 km off axis and 200 m above the ridge-crest topography. Near the northern limit of the study region, the Lamont Seamount Chain rises from the western ridge flank and restricts along-EPR flow to five narrow passages, where peak velocities in excess of 20 cm·s −1 were observed. Outside the region of the ridge-crest boundary currents the density field over the EPR near 10 • N is characterized by isopycnals dipping into the ridge flanks. Directly above the EPR axis the ridge-crest boundary currents give rise to an isopycnal dome. During times of strong westward cross-EPR flow isopycnal uplift over the eastern flank causes the cross-ridge density field below the doming isopycnals to be asymmetric, with higher densities over the eastern than over the western flank.

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Section: Discussionsupporting

confidence: 60%

Section: Discussionmentioning

confidence: 99%

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

Thurnherr

Ledwell

Lavelle

et al. 2011

Deep Sea Research Part I: Oceanographic Research Papers

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show abstract

“…However, the timing and directions of bending are inconsistent with regional analysis of tidal flow [Cannon and Pashinski, 1997], tidal models (H. Mofjeld, personal communication, 2004), and current meter observations (range 0.05 m/s-0.10 m/s [Thomson et al, 1989[Thomson et al, , 2003Williams and Tivey, 2001]). The inconsistency may be related to perturbation of the flow field by proximity to the west wall of the axial valley.…”

Section: Resultsmentioning

confidence: 99%

Entrainment and bending in a major hydrothermal plume, Main Endeavour Field, Juan de Fuca Ridge

Rona

Bemis

Jones

et al. 2006

Geophysical Research Letters

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[1] We measure expansion rate and bending in a 23-hour time series of acoustic images of the lower 25 m section of a buoyant hydrothermal plume rising from Grotto vent in the Main Endeavour Field, Juan de Fuca Ridge. We then calculate entrainment coefficient, the constant of proportionality relating mean inflow velocity at the plume edge to maximum mean upward velocity within the plume. The plume section alternately bends southwest at relatively high inclinations (37°) and northeast at lower inclinations at irregular intervals twice during this time period, apparently driven by current reversals in the mixed semi-diurnal tidal cycle. The measured expansion rates (0.11 -0.25 m/m) and calculated entrainment coefficients (0.07 -0.18) are directly proportional to the degree of bending (R 2 = 0.75). The loss of buoyancy flux related to enhanced mixing in a stratified environment during bending may contribute to reduction of potential rise height consistent with predicted ($400 m) and measured (300 -350 m) plume tops. Citation: Rona, P. A.,

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“…An expanded view of hydrography and the effect of the ridge comes from a cross-ridge transect [Cannon and Pashinski, 1997] Cannon and Thomson, 1996]. In this case and for spectral representations to follow, current component time series were demeaned and detrended, cosine tapered over the first and last 10% of the record, Fourier analyzed, and the resulting periodograms were smoothed using an l 1-point Hanning spectral window [Emery and Thomson, 1997].…”

Section: Physical Setting and Observational Resultsmentioning

confidence: 99%

“…The ridge locally intensifies both mean [Cannon and Pashinski, 1997] and subinertial flow. The model identifies one mechanism for the intensification of subinertial oscillations as an along-ridge near-geostrophic response to the cyclic cross-ridge transport and the associated downward displacement of isopycnals alternately on each side of the ridge.…”

Section: Ridge Effects On Flowmentioning

confidence: 99%

On subinertial oscillations trapped by the Juan de Fuca Ridge, northeast Pacific

Lavelle¹,

Cannon²

2001

J. Geophys. Res.

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Variations in mean currents affecting hydrothermal plumes on the Juan de Fuca Ridge

Cited by 36 publications

References 17 publications

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

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

Entrainment and bending in a major hydrothermal plume, Main Endeavour Field, Juan de Fuca Ridge

On subinertial oscillations trapped by the Juan de Fuca Ridge, northeast Pacific

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