Ocean internal wave spectra inferred from seismic reflection transects

Holbrook, W. Steven; Fer, Ilker

doi:10.1029/2005gl023733

Cited by 119 publications

(117 citation statements)

References 29 publications

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“…Temperature-salinity contrasts in the water column result in small changes in sound speed and appear in seismic images as distinct reflection layers revealing exceptional detail between 10-100 m horizontal resolution throughout the water column. Spectacular images of thermohaline finestructure in the ocean include features such as intrusions (Holbrook et al, 2003), fronts (Holbrook et al, 2003;Nakamura et al, 2006), water mass boundaries (Nandi et al, 2004), internal waves (Holbrook and Fer, 2005;Krahmann et al, 2008), internal tide characteristics ) and mesoscale eddies (Biescas et al, 2008;Pinheiro et al, 2010). A clear relationship has been established between recorded seismic reflectance and the presence of thermohaline finestructure (Nandi et al, 2004).…”

Section: Introductionmentioning

confidence: 97%

“…Vertical displacements of reflections from oceanic finestructure recorded in the Norwegian Sea were shown to be representative of the internal wave field (Holbrook and Fer, 2005). In order to infer the internal wave energy level from spectral analysis, we digitized representative reflection horizons at 12.5 m horizontal resolution, and categorized them into groups based on their proximity to the staircase.…”

Section: Spectral Analysismentioning

confidence: 99%

“…11. Following Holbrook and Fer (2005), we compare ensembleaveraged horizontal wavenumber spectra of reflection displacement to the Garrett-Munk tow spectrum (GM75, Garrett and Munk, 1975), as described in Katz and Briscoe (1979).…”

Section: Weak Turbulencementioning

confidence: 99%

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Seismic imaging of a thermohaline staircase in the western tropical North Atlantic

et al. 2010

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Abstract. Multichannel seismic data acquired in the Lesser Antilles in the western tropical North Atlantic indicate that the seismic reflection method has imaged an oceanic thermohaline staircase. Synthetic acoustic modeling using measured density and sound speed profiles corroborates inferences from the seismic data. In a small portion of the seismic image, laterally coherent, uniform layers are present at depths ranging from 550-700 m and have a separation of ∼ 20 m, with thicknesses increasing with depth. The reflection coefficient, a measure of the acoustic impedance contrasts across these reflective interfaces, is one order of magnitude greater than background noise. Hydrography sampled in previous surveys suggests that the layers are a permanent feature of the region. Spectral analysis of layer horizons in the thermohaline staircase indicates that internal wave activity is anomalously low, suggesting weak internal waveinduced turbulence. Results from two independent measurements, the application of a finescale parameterization to observed high-resolution velocity profiles and direct measurements of turbulent dissipation rate, confirm these low levels of turbulence. The lack of internal wave-induced turbulence may allow for the maintenance of the staircase or may be due to suppression by the double-diffusive convection within the staircase. Our observations show the potential for seismic oceanography to contribute to an improved understanding of occurrence rates and the geographical distribution of thermohaline staircases, and should thereby improve estimates of vertical mixing rates ascribable to salt fingering in the global ocean.

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Section: Introductionmentioning

confidence: 97%

Section: Spectral Analysismentioning

confidence: 99%

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Seismic imaging of a thermohaline staircase in the western tropical North Atlantic

et al. 2010

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“…Internal wave is ocean interior wave due to changes in hydrostatic balance [13]. Internal waves are generated when interfaces between layers of different water densities are disrupted, usually due to differences in temperature and/or salinity [12]. In addition, tilted reflector is observed at 150-500 m depth (black ellips area).…”

Section: Resultsmentioning

confidence: 99%

Application of multichannel seismic reflection method to measure temperature in Sulawesi Sea

Fajaryanti

Manik

Purwanto³

2018

IOP Conf. Ser.: Earth Environ. Sci.

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Abstract. Seismic oceanography is integrated discipline between seismology and physical oceanography that can be used to investigate phenomenon in water column. Seismic oceanography displays fine structure of water column seismically and in wide range. The aim of this research was to measure temperature in Sulawesi Sea with CTD and seismic data. The benefits of this research were to create integrity and effectiveness in seismic and oceanographic surveys as well as to help develop OTEC (Ocean Thermal Energy Conversion) studies in Indonesia. The acquisition of seismic and CTD data in line 17 Sulawesi Sea conducted by P3GL on Mei-Juni 2016. Data processing was conducted in Februari-April 2017 and divided into three processes: seismic data processing using ProMax 2D software, synthetic seismogram processing using Hampson-Russell software, and mapping temperature using Ocean Data View software. The results showed that temperature in Sulawesi Sea based on CTD data ranged 4.7-30.3 Ԩ, and temperature based on the sesimic data ranged 4.49-30.29 ԨǤ This difference occured due to difference in vertical sampling between CTD and sound velocity semblance. Acoustic impedance in Sulawesi Sea ranged 1.529-1.578 MRy. Vertical and horizontal resolution of seismic data in this research were 6.3 m and 93.5 m, respectively. It's well established that sound velocity the main contribution to acoustic impedance. Correlation between seismic field with synthetic seismogram from CTD data is 0.7. IntroductionThe information about physical oceanography can be obtained by satellite imagery, ground check, and acoustic survey. Thermohaline circulation is the primary forcing mechanism that keeps the ocean conveyor belt in perpetual motion, regarding ocean processes helps build a comprehensive understanding of the ocean's role in the distribution of heat around the planet and thereby affecting climate. Seismic oceanographer investigate oceanic thermohaline finestructure based on temperature and salinity profiles [1].Seismic method is one of sea exploration method based on measurement of sound waves propagating on earth layer medium then reflected and refracted [2]. Seismic method has three application with different requirements for band-width and depth-width; engineering seismology, exploration seismology, and earthquake seismology. Engineering seismology is used to derive a velocity-depth model for near surface with bandwidth 1000 Hz and depth down to 1 km. Exploration seismology is used to derive an image of subsurface with bandwidth 100 Hz and depth of interest down to 10 km. Earthquake seismology is used to investigate oceanic and continental crust with bandwith 10 Hz and depth of interest down to 100 km [3].Seismic oceanography is recently developed approach for investigating water column using seismic reflection method. This method utilizies vibration source from air gun and fired to water, the waves are exposed to the medium and energy. This propagation will be influenced by many factors, such as offset,

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“…Gibson et al, 2007). One of these alternative techniques is the multichannel seismic (MCS) system, an acoustic method providing quasi-synoptic images of the thermohaline boundaries in the ocean interior to full ocean depth, with a lateral resolution of up to ~10 1 m (Holbrook and Fer, 2005).…”

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confidence: 99%

High-resolution diapycnal mixing map of the Alboran Sea thermocline from seismic reflection images

Moncada¹,

Sallarès²,

Biescas³

2017

Preprint

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Abstract. The Alboran Sea is a dynamically active region where the salty and warm Mediterranean water first encounters the incoming milder and cooler Atlantic water. The interaction between these two water masses originates a set of sub-mesoscale structures and a complex sequence of processes that entail mixing close to the thermocline. Here we present a high-resolution map of 15 the diapycnal diffusivity around the thermocline depth obtained using acoustic data recorded with a high-resolution multichannel seismic system. The map reveals a patchy thermocline, with areas of strong diapycnal mixing juxtaposed with others of weaker mixing. The patch size is of a few kms in the horizontal scale and of 10-15 m in the vertical one. The comparison of the obtained maps with the original acoustic images shows that vigorous mixing tends to occur in areas of 20 internal wave instability, whereas mixing levels in more stable areas is lower. These results are also compared with others obtained using conventional probes. The values obtained using the two methods agree within uncertainty bounds, and they are also consistent with reference theoretical values. Overall, our results demonstrate that high-resolution seismic systems allow to remotely quantify mixing at the thermocline depth with a lateral resolution of O(10 1 m). 25

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Ocean internal wave spectra inferred from seismic reflection transects

Cited by 119 publications

References 29 publications

Seismic imaging of a thermohaline staircase in the western tropical North Atlantic

Seismic imaging of a thermohaline staircase in the western tropical North Atlantic

Application of multichannel seismic reflection method to measure temperature in Sulawesi Sea

High-resolution diapycnal mixing map of the Alboran Sea thermocline from seismic reflection images

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