Imaging meddy finestructure using multichannel seismic reflection data

Biescas, Berta; Sallarès, Valentı́; Pelegrí, Josep Lluís; Machín, Francisco; Carbonell, Ramón; Buffett, Grant; Dañobeitia, Juan José; Calahorrano, Alcinoe

doi:10.1029/2008gl033971

Cited by 105 publications

(105 citation statements)

References 18 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%

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%

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

et al. 2010

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“…According to figure 10, salinity changes affect the change of synthetic seismogram character at 100-200 m depth, while temperature changes affect the change of synthetic seismogram character at 100-600 m depth. [15] estimates that reflection seismic derived from 90-95% sound velocity and 5-10% density and the contribution of temperature is 80% while salinity is 20%. [8] is also mention that the contribution of temperature is 83% and salinity is 17%.…”

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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“…AAIW are located immediately under the NACW (at the depth interval 600<z<1000 m and the neutral-density interval 27.2<γ n <27.65 kg m −3 ), being recognizable through a salinity minimum (salinities are less than 35.5, or fresher than the deepest NACW) and an intense phosphate maximum (concentrations are well in excess of 1.25 µmol kg −1 ) (Machín et al 2006, Machín and Pelegrí 2009, Pastor et al 2012. Meddies in the Canary Basin are located immediately below the AAIW level (1000<z<1500 m and 27.6<γ n <27.8) (Biescas et al 2008), and are characterized by positive salinity anomalies (values as high as 36.5) and negative phosphate anomalies (concentrations as low as 0.7 µmol kg −1 ) (Pastor et al 2012).…”

Section: Methodsmentioning

confidence: 99%

Interaction of Mediterranean Water lenses with Antarctic Intermediate Water off Northwest Africa

Machín¹,

Pelegrí²

2016

Sci. Mar.

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Summary:Mediterranean Water lenses (meddies) in the eastern North Atlantic, north of the Canary Islands, appear to often have their salty and nutrient-poor core accompanied by relatively fresh and nutrient-rich waters on top. We describe several occurrences of freshwater halos and berets for meddies sampled north of the Canary Islands-with instrumented moorings, Argo floats and oceanographic cruises-and identify the source of these fresh anomalies as diluted Antarctic Intermediate Water (AAIW). We propose that this capping takes place off Northwest Africa, as the southward-advected meddy interacts with the northward-advected AAIW. This interpretation is consistent with a simple analysis of the relevant advectivediffusive time scales associated with the passage of meddies under a layer of AAIW, and suggests that meddies may be a mechanism for AAIW export far into the North Atlantic Ocean.Keywords: meddies; Antarctic Intermediate Water; eastern North Atlantic. Interacción de remolinos de agua mediterránea con Agua Intermedia Antártica al noroeste de ÁfricaResumen: Los Meddies en el Atlántico Norte oriental, al norte de las Islas Canarias, a menudo parecen tener su núcleo salado y pobre en nutrientes acompañado de aguas relativamente frescas y ricas en nutrientes en la parte superior. Se describen varios casos de halos y boinas de agua dulce para meddies muestreados al norte de las Islas Canarias -con instrumentos anclados, perfiladores Argo y campañas oceanográficas-identificando así el origen de estas anomalías frescas como Agua Intermedia Antártica (AIAA) diluida. Proponemos que esta interacción se lleva a cabo en el noroeste de África, cuando el meddy advectado hacia el sur interactúa con el AIAA advectada hacia el norte. Esta interpretación es coherente con un simple análisis de las escalas de tiempo advectivo-difusivas asociadas con el paso de meddies bajo una capa de AIAA, y sugiere que los meddies pueden ser un mecanismo para exportar AIAA hacia el océano interior en el Atlántico Norte.Palabras clave: meddies; agua intermedia antártica; Atlántico Norte oriental.Citation/Como citar este artículo: Machín F

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Imaging meddy finestructure using multichannel seismic reflection data

Cited by 105 publications

References 18 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

Interaction of Mediterranean Water lenses with Antarctic Intermediate Water off Northwest Africa

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