Geostatistical Seismic Inversion for Temperature and Salinity in the Madeira Abyssal Plain

Azevedo, Leonardo; Matias, L.; Turco, Francesco; Tromm, Renan; Peliz, Álvaro

doi:10.3389/fmars.2021.685007

Cited by 8 publications

(6 citation statements)

References 67 publications

(87 reference statements)

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“…The first is to attenuate the direct arrival effect. The second is to preserve the relative amplitudes of the water reflections to be later used in quantitative studies (i.e., seismic inversion) 5 , 32 . To reach these objectives, the raw data was processed to remove low signal-to-noise ratio seismic traces, apply the acquisition geometry definition, filter noise, attenuate the direct arrival using a combination of linear move out, horizontal median filtering and amplitude subtraction and to correct for the spherical divergence.…”

Section: Methodsmentioning

confidence: 99%

“…Vertical ocean temperature and salinity profiles analyzed in Azevedo et al 5 , van der Boog et al 6 and You 7 suggest the presence of double diffusion features, such as thermohaline staircases, in the MAP region. Thermohaline staircases are associated with small-scale double-diffusive mixing that convert the quasi-continuous vertical temperature and salinity profiles into step-like layered structures consisting of abrupt changes in temperature and salinity, separating regions where the temperature and salinity fields are relatively constant 4 , 8 , 9 .…”

Section: Introductionmentioning

confidence: 95%

See 1 more Smart Citation

Acoustic imaging of stable double diffusion in the Madeira abyssal plain

Duarte,

Peliz,

Matias

et al. 2024

Sci Rep

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Sub-mesoscale and mesoscale (i.e., 1–10 km and 10–200 km, respectively) ocean processes are highly relevant for the understanding of global circulation, mixing of water masses and energy exchange between ocean layers. However, the processes happening at these scales are hard to be characterized using direct measurements of temperature and salinity. Direct measurements are obtained from vertical probes and/or autonomous vehicles, which, despite their high vertical resolution, are sparsely located in space and therefore unable to capture spatial details at these scales. Seismic oceanography (SO) data have been successfully used to imaging and characterize the ocean at these spatial scales. These data represent indirect measurements of the ocean temperature and salinity along kilometric transects with high horizontal resolution (i.e., a near-synaptic view of the system under investigation), but lower vertical resolution when compared with direct observations. Despite its complex oceanographic setting, the Madeira Abyssal Plain is still largely uncharacterized due to the lack of direct observations. We show for the first time a comprehensive processing, modelling and interpretation of three 2-D seismic oceanography sections from this region. The data show coherent seismic reflection in space, depth and time and shed light into this oceanographic setting with an unprecedent horizontal resolution. The SO modelling and interpretation are combined with existing direct measurements and a quantitative method to correlate thermohaline staircases interpreted from conductivity-temperature-depth casts and seismic reflections is proposed. The results show the relatively stable presence of thermohaline staircases in simultaneously time and space between 1200 and 2000 m of water depth and their spatial variability and contribute to the generalization of SO in physical oceanography.

show abstract

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 95%

Acoustic imaging of stable double diffusion in the Madeira abyssal plain

Duarte,

Peliz,

Matias

et al. 2024

Sci Rep

Self Cite

View full text Add to dashboard Cite

show abstract

“…The rst to attenuate the direct arrival effect. The second is to preserve the relative amplitudes of the water re ections to be later used in quantitative studies (i.e., seismic inversion) 4,31 . To reach these objectives, the raw data was processed to remove low signal-to-noise ratio seismic traces, apply the acquisition geometry de nition, lter noise, attenuate the direct arrival using a combination of linear moveout, horizontal median ltering and amplitude subtraction and to correct for the spherical divergence.…”

Section: Seismic Oceanography Data Processingmentioning

confidence: 99%

“…Vertical ocean temperature and salinity pro les analyzed in Azevedo et al 4 , van der Boog et al 5 and You et al 6 suggest the presence of double diffusion features, such as thermohaline staircases, in the MAP region. Thermohaline staircases are associated with small-scale double-diffusive mixing that convert the quasi-continuous vertical temperature and salinity pro les in steps-like layering of abrupt changes in temperature and salinity, followed by constant values through depth 7,8,9 .…”

Section: Introductionmentioning

confidence: 96%

Acoustic imaging of stable double diffusion in the Madeira abyssal plain

Duarte,

Peliz,

Matias

et al. 2024

Preprint

Self Cite

View full text Add to dashboard Cite

Sub-mesoscale and mesoscale (i.e., 1-10km and 10-200km, respectively) ocean processes are highly relevant for the understanding of global circulation, mixing of water masses and energy exchange between ocean layers. However, the processes happening at these scales are hard to be characterized using direct measurements of temperature and salinity. Direct measurements are obtained from vertical probes and/or autonomous vehicles, which, despite their high vertical resolution, are sparsely located in space and therefore unable to capture spatial details at these scales. Seismic oceanography (SO) data have been successful used to imaging and characterize the ocean at these spatial scales. These data represent indirect measurements of the ocean temperature and salinity along kilometric transects with high horizontal resolution (i.e., a near-synaptic view of the system under investigation), but lower vertical resolution when compared with direct observations. Despite its complex oceanographic setting, the Madeira Abyssal Plain is still largely uncharacterized due to the lack of direct observations. We show for the first time a comprehensive processing, modelling and interpretation of three 2-D seismic oceanography sections from this region. The data show coherent seismic reflection in space, depth and time and shed light into this oceanographic setting with an unprecedent horizontal resolution. The SO modelling and interpretation are combined with existing direct measurements and a quantitative method to correlate thermohaline staircases interpreted from conductivity-temperature-depth casts and seismic reflections is proposed. The results show the relatively stable presence of thermohaline staircases in simultaneously time and space between 1200–2000 m of water depth and their spatial variability and contribute to the generalization of SO in physical oceanography.

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“…The temperature distribution along each seismic section is calculated using an adapted iterative method (Papenberg et al, 2010;Gunn et al, 2018Gunn et al, , 2020. Acoustic inverse schemes that rely upon densely sampled hydrographic measurements are less easy to exploit since coincident observations of temperature and salinity are unavailable (Azevedo et al, 2021). Instead, we use a pragmatic approach that side-steps this limitation and takes advantage of the dominant dependency of acoustic sound speed upon temperature.…”

Section: Seismically Determined Propertiesmentioning

confidence: 99%

Vertical Mixing and Heat Fluxes Conditioned by a Seismically Imaged Oceanic Front

et al. 2021

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The southwest Atlantic gyre connects several distinct water masses, which means that this oceanic region is characterized by a complex frontal system and enhanced water mass modification. Despite its significance, the distribution and variability of vertical mixing rates have yet to be determined for this system. Specifically, potential conditioning of mixing rates by frontal structures, in this location and elsewhere, is poorly understood. Here, we analyze vertical seismic (i.e., acoustic) sections from a three-dimensional survey that straddles a major front along the northern portion of the Brazil-Falkland Confluence. Hydrographic analyses constrain the structure and properties of water masses. By spectrally analyzing seismic reflectivity, we calculate spatial and temporal distributions of the dissipation rate of turbulent kinetic energy, ε, of diapycnal mixing rate, K, and of vertical diffusive heat flux, FH. We show that estimates of ε, K, and FH are elevated compared to regional and global mean values. Notably, cross-sectional mean estimates vary little over a 6 week period whilst smaller scale thermohaline structures appear to have a spatially localized effect upon ε, K, and FH. In contrast, a mesoscale front modifies ε and K to a depth of 1 km, across a region of O(100) km. This front clearly enhances mixing rates, both adjacent to its surface outcrop and beneath the mixed layer, whilst also locally suppressing ε and K to a depth of 1 km. As a result, estimates of FH increase by a factor of two in the vicinity of the surface outcrop of the front. Our results yield estimates of ε, K and FH that can be attributed to identifiable thermohaline structures and they show that fronts can play a significant role in water mass modification to depths of 1 km.

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Geostatistical Seismic Inversion for Temperature and Salinity in the Madeira Abyssal Plain

Cited by 8 publications

References 67 publications

Acoustic imaging of stable double diffusion in the Madeira abyssal plain

Acoustic imaging of stable double diffusion in the Madeira abyssal plain

Acoustic imaging of stable double diffusion in the Madeira abyssal plain

Vertical Mixing and Heat Fluxes Conditioned by a Seismically Imaged Oceanic Front

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