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Internal waves above Great Meteor Seamount

The Great Meteor Seamount is an isolated submarine mountain in the Canary Basin. Its top is 500m below water, whereas the surrounding abyssal plain is 4000m deep. When the barotropic tide hits the seamount, the isopycnals are pushed up and down the slope of the mountain and vigourous internal tides are generated.

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The Great Meteor Seamount
Color represents the slope of the bottom. The pink triangle is the expected direction of propagation of the internal waves.

Simultaneous ADCP and temperature measurements were performed during 19 days at a rate of 1 Hz. Using the high accuracy of the NIOZ High Sampling Rate Thermistors (1mK), strong nonlinear internal waves fronts are observed in phase with M2, as well as continuous short period isotherm motions eventually showing nonlinear instability.

During the downslope phase of the flow, Kelvin-Helmholtz instabilities are observed, with O(10m) billows.

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TIme series of temperature
Anels b and c correspond to successive zooms into panel a.

Using the Thorpe scale, eddy diffusivity can be estimated. Averaged over a fortnight, the observed overall time-depth mean Kz = 3.10-3 m2 s-1. Variations with time and depth are large, by up to four orders of magnitude

Backscattered echo intensity data are compared to a specifically written attenuation law, and anomalies appear tobe strongly correlated to internal waves activity, inferring a resuspension of materials by the fronts.

H. van Haren and L. Gostiaux, A deep-ocean Kelvin-Helmholtz billow train, Geophys. Res. Lett., vol. 31, L03605 (2010)

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