Open-ocean-interior moored sensor turbulence estimates, below a Meddy
In: Deep-Sea Research, Part I. Oceanographic Research Papers. Elsevier: Oxford. ISSN 0967-0637; e-ISSN 1879-0119, more
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| Author keywords |
Moored high-resolution temperature observations; Canary Basin NE-Atlantic Ocean; Ocean-interior turbulence estimates; Smooth stratification underneath Meddy; Episodic internal wave breaking; Near-inertial shear |
| Abstract |
A one-year time series of moored high-resolution temperature T-sensor data from 1455 ± 65 m depth on a 3900 m long line in about 5300 m of water in the NE-Atlantic Canary Basin are dominated by salinity (over-)compensated intrusions arising from the effects of Mediterranean outflow waters, which are commonly organized as underwater eddy-lenses ‘Meddies’. During the passage of a Meddy-core above the T-sensors, no intrusions were observed, thereby making it possible to use the temperature records to quantify turbulence parameters. Mean turbulence values confirm previous shipborne profiler estimates of O(10-10) m2 s-3 and O(10-5) m2 s-1 for dissipation rate and eddy diffusivity, respectively. The present data show that these ocean-interior turbulence estimates are from short-lived (<0.5 h) rather intense overturning cells with vertical scales of <5 m. Because the turbulence inertial subrange is found to extend into the internal wave band, the overturns are predominantly driven by shear associated with inertial currents. Kinetic energy, current shear and temperature variance peak at sub-inertial frequencies during the Meddy passage, suggesting wave trapping in the warm anti-cyclonic eddy and/or weakly stratified layers. The observations further show that internal wave displacements are coherent over vertical scales of up to 40 m during the presence of the Meddy compared with vertical coherence scales of <25 m during the more common no-Meddy conditions of double diffusion intrusions. |
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