Characteristics of internal waves within thermohaline staircase region in the Caribbean Sea

Abstract

Thermohaline staircases play a crucial role in the vertical transport of heat and salt in the thermocline. However, there are few in-situ observations of internal waves within thermohaline staircases. The seismic method offers high horizontal resolution and full ocean depth images over large volumes of the ocean, which can enable the visualization of internal waves within the thermohaline staircase region. In this paper, we characterize and analyze internal waves within thermohaline staircases in the Caribbean Sea using two-dimensional seismic data. Snapshots of fine structure displacements caused by internal waves are captured. We calculate the horizontal wavenumber spectra of the vertical displacement of internal waves, which closely align with the Garrett-Munk tow spectrum, indicating features of background internal wave field. We employed the Empirical Mode Decomposition (EMD) method to analyze vertical displacement data of internal waves derived from seismic data and obtained new results. The internal waves within thermohaline staircases consist of some dominant wavelength components of around 0.34 km, 0.83 km, 1.8 km, 6.25 km, 12.5 km, and 25 km. Wavelengths of approximately 0.34 km, 0.83 km, 1.8 km, and 6.25 km are coupled between the upper and lower sections, indicating the vertical transmission of the energy of high-wavenumber internal waves. By applying the prestack migration method, we observed that internal waves within thermohaline staircases display a staggered pattern. Except for the fractured strip structure, other reflectors show subtle alterations, suggesting that the thermohaline staircase stays stable during the acquisition period. Seismic oceanography emerges as a reliable method for studying internal wave characteristics within thermohaline staircases. It has the capacity to facilitate research on the complex dynamics of the ocean at multiple scales.