Near-inertial motions over a mid-ocean ridge: Effects of topography and hydrothermal plumes

Journal Article · Tue May 15 00:00:00 EDT 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JC095iC05p07261· OSTI ID:5009654

Thomson, R E ^[1]; Roth, S E; Dymond, J ^[2]

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1. Inst. of Ocean Sciences, Sidney, British Columbia (Canada)
2. Oregon State Univ., Corvallis (United States)

The authors investigate the spatial structure of near-inertial motions in the vicinity of the Endeavour segment of Juan de Fuca Ridge (approximately 48{degree}N, 129{degree}W) in the northeast Pacific Ocean. Within the lower 1,000 m of the water column where most of the observations were obtained, near-inertial oscillations have rms current speeds of O(1 cm/s) and vertical isotherm displacements of O(10 m). The fluctuations are confined to the frequency band 0.966-1.079 f (f is the local Coriolos parameter) and have characteristic event durations of 1 week. Marked alteration of the near-inertial current amplitudes occurs over two well-defined depth zones within the study region. Within the 200-m zone immediately above the 2,100-m ridge crest, current amplitudes are amplified by a factor of 1.2-1.7 because of bottom reflection and/or scattering of the downward propagating energy. Evidence that the amplification may be linked to bottom reflection rather than to scattering is provided by flattening and cross-slope rotation of the near-inertial current ellipses with increased proximity to the top of the ridge. Near-inertial motions are estimated to have vertical coherence scales of the order of 10-100 m, while horizontal coherence scales exceed the 50-km separation between the mooring locations. Minimum vertical and horizontal coherences are found for the depth zone 1,600-1,800 m, while maximum correlation occurs for near-bottom motions immediately above the crest of the ridge. Weak near-inertial motions are observed within the 100-m-deep axial valley.

• OSTI ID: 5009654
• Journal Information: Journal of Geophysical Research; (United States), Vol. 95:C5; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GEOLOGIC FORMATIONS
TOPOGRAPHY
PACIFIC OCEAN
WATER CURRENTS
FLOW RATE
AMPLITUDES
DEPTH
FLUCTUATIONS
GEOLOGIC STRUCTURES
GEOMORPHOLOGY
HYDROTHERMAL SYSTEMS
MOTION
OCEANOGRAPHY
OSCILLATIONS
REFLECTIVITY
SCATTERING
CURRENTS
DIMENSIONS
ENERGY SYSTEMS
GEOLOGY
GEOTHERMAL SYSTEMS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
SEAS
SURFACE PROPERTIES
SURFACE WATERS
VARIATIONS
580000* - Geosciences