SEISSEA

Seismic Inversion and Stochastic Spectral Analysis of Thermohaline Staircases in the Tyrrhenian Sea

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 Obiettivo del progetto (Objective)

'Seismic oceanography is the application of seismic reflection profiling together with conventional oceanographic techniques to the study of physical oceanographic processes. Seismic oceanography data were acquired in April and May, 2010 in the Tyrrhenian Sea and imaged so-called thermohaline staircases. Thermohaline staircases are regular, well-defined, step-like variations in vertical temperature and salinity gradients that form when temperature and salinity increase with depth and nearly compensate with density. They are important indicators of mixing processes such as double-diffusive convection.

The candidate proposes the development of three new seismic oceanography techniques: a) advanced seismic data analysis, b) inversion of seismic data to obtain estimates of temperature, salinity and sound speed, and c) stochastic spectral analysis, which will allow discrimination between areas dominated by turbulence and those dominated by internal waves and provide estimates of their associated scale lengths.

The results of this project will undoubtedly advance the tools of seismic oceanography and will provide some of the constraints necessary to generate ocean circulation models. Since the ocean is responsible for a large portion of heat redistribution, the results will also be useful to climate scientists whom use circulation models in the study of climate change.'

Introduzione (Teaser)

Marine scientists have studied mixing processes in stable ocean regions with the aim of building better models of ocean circulation. These models will enable the construction of more accurate climate change models.

Descrizione progetto (Article)

The 'Seismic inversion and stochastic spectral analysis of thermohaline staircases in the Tyrrhenian Sea' (SEISSEA) project investigated the use of seismic oceanography (SO) to study mixing processes in the most stable regions of the oceans. These regions where temperature and salinity vary vertically in a step-like manner are known as a thermohaline staircase. SO uses multi-channel seismic reflection profiling together with conventional oceanography to investigate physical oceanographic processes.

SEISSEA used SO to study the thermohaline staircases, which are important indicators of mixing processes. The work was conducted in the Tyrrhenian Sea, situated off the west coast of Italy. The centre of the Tyrrhenian Sea is largely free from external turbulence and mass convection and is known to contain well-defined stratified layers of varying temperature. Therefore, it is a natural laboratory for studying diapycnal mixing, which is defined as mixing across lines of equal density.

The second part of the study involved extraction of the Hurst number (which characterises the roughness of surfaces) from the seismic data. SEISSEA found that the Hurst number can be used to estimate internal wave number spectra directly from seismic data. This is of great interest to physical geographers because until now wave number spectra were obtained using measurements from oceanic probes.

Work conducted by SEISSEA provided new advanced tools for SO and help to generate ocean circulation models. As the ocean is responsible for a large portion of heat re-distribution, the project's findings will help climate scientists who use circulation models to study climate change.