Mapping non-local turbulent breakdown of oceanic lee waves offshore Costa Rica through seismic oceanography

Abstract

Data analysis techniques in Seismic Oceanography are rapidly becoming more complex. Beyond first-order observation of oceanic structures, it is possible to extract quantifiable information about internal wave energies and turbulent dissipation rates. We use two co-located seismic surveys taken one day apart to estimate turbulent diffusivities of lee wave breakdown with emphasis on the mid-water turbulence generated. Through a horizontal wavenumber spectral analysis of our seismic images, we estimate turbulent dissipation rates throughout the cross-section. By integrating horizontal seismic slope spectra in the wavenumber domain over the turbulent subrange, we obtain relative turbulent energies across the survey. To resolve absolute turbulent diffusivities, we scale the relative measures to known absolute energies from tracked seismic reflectors (isopycnals). The analysis section spans 22 km laterally and full ocean depth with a resolution on turbulent diffusivity of 10 m vertically by 400 m laterally. We focus on the region of elevated turbulent diffusivity caused by the breakdown of the lee wave above its generating site. We find the turbulent diffusivities related to the lee wave breakdown to be about five times greater than surrounding waters and 15 times greater than average open ocean diffusivities. We also see increased turbulent diffusivity around the rough bathymetry.

Estimation of Temperature and Salinity from Marine Seismic Data—A Two-Step Approach

“…Temperature and salinity variations within water-column structures produce visible reflections on the recorded seismic data, which, in turn, allows for imaging of structures like ocean fronts, mesoscale eddies, and Lee waves [12][13][14][15][16]. In addition, dynamic processes such as ocean turbulence [17][18][19] and the movement of water masses [20,21] have also been recorded from these reflections. These techniques are sensitive to oceanic sound-speed variations [22] and can be applied to both two-and three-dimensional (2D and 3D) offshore seismic data [23].…”