Image of a subsurface current core in the southern South China Sea

Tang, Qunshu; Wang, D. X.; Li, J. B.; Yan, Ping; Li, J.

doi:10.5194/os-9-631-2013

Cited by 9 publications

(4 citation statements)

References 37 publications

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“…A recently developed method ''seismic oceanography'' based on the conventional seismic reflection profiling allows us to relate water column acoustic reflections to oceanic finescale structures [e.g., Holbrook et al, 2003;Ruddick et al, 2009]. It has the capability of showing the mesoscale to finescale features simultaneously with a typical vertical and horizontal resolution of 10 m. Numerous oceanographic features can be outlined successfully, such as subsurface eddies [Biescas et al, 2008;Buffett et al, 2009;Menesguen et al, 2012;Papenberg et al, 2010], currents [Tang et al, 2013;Tang and Zheng, 2011;Vsemirnova et al, 2012], internal waves [Holbrook and Fer, 2005;Krahmann et al, 2008], and thermohaline staircases [Biescas et al, 2010;Fer et al, 2010].…”

Section: Citationmentioning

confidence: 99%

Seismic observations from a Yakutat eddy in the northern Gulf of Alaska

2014

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Recent works show that the seismic oceanography technique allows us to relate water column seismic reflections to oceanic finescale structures. In this study, finescale structures of a surface anticyclonic eddy have been unveiled by reprocessing two seismic transects acquired in the northern Gulf of Alaska using an 8 km hydrophone streamer and 6600 cu in linear airgun array in September 2008. The eddy was a typical bowl-like structure with around 55 km width and 700 m depth. It has two fringes around the eddy base and a spiral arm at the NE edge. The in situ sea surface temperature and salinity data from a shipboard thermosalinograph help to confirm our interpretations of a spiral arm shed from the warm eddy and the entrained cold water from elsewhere. Nearby the eddy and offshore the shelf-break, there is a strong frontal feature, probably the Alaska Current. The eddy likely formed offshore Yakutat shelf and transported along the offshore shelf-break by tracking the sea level anomalies. Its equivalent diameter of 65 km was measured using the along-track altimeter and the seismic constraints. It was comparable with results from the representative conventional algorithms of eddy detection. Geostrophic velocities of the eddy were estimated from the dipping seismic reflections under the assumptions of approximate isopycnals and geostrophic balance. Measured water properties including sea surface temperature, salinity, and chlorophyll revealed that eddy translation transports coastal water to the pelagic regions. Structures synthesized from CTD profiles that sampled an earlier eddy suggest that thin striae around the base might be a common feature in Gulf of Alaska eddies.

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Section: Citationmentioning

confidence: 99%

Seismic observations from a Yakutat eddy in the northern Gulf of Alaska

2014

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“…It can also provide information about the three-dimensionality of structures as well as temporal changes, on a scale ranging from hours to seasons and potentially to years. The method has been applied to the examination of fronts, water masses, currents, eddies, thermohaline intrusions and staircases, internal waves, and mixing processes (e.g., Biescas et al, 2008;Sheen et al, 2009;Blacic and Holbrook, 2010;Pinheiro et al, 2010;Tang et al, 2013;Tang et al, 2014;Buffett et al, 2017;Gorman et al, 2018;Ruddick, 2018).…”

Section: Introductionmentioning

confidence: 99%

Temporal Variability of Thermohaline Fine-Structure Associated With the Subtropical Front Off the Southeast Coast of New Zealand in High-Frequency Short-Streamer Multi-Channel Seismic Data

et al. 2021

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Seismic oceanography generally makes use of multi-channel seismic reflection data sourced by air gun arrays and long hydrophone streamers to image oceanographic water masses and processes—often piggybacking on surveys that target deeper geological features below the seafloor. However, due to the acquisition methods employed, shallow (upper 200 m or so) regions of the ocean can be poorly imaged with this technique, and resolution is often lower than desirable for imaging fine-structure within the water column. In 2012, we collected a set of higher-resolution seismic lines off the southeast coast of New Zealand, with a generator-injector airgun source and hydrophone streamer configuration designed to improve images of shallower water masses and their boundaries. The seismic lines were acquired with coincident expendable bathythermograph deployments which provides direct ties between physical oceanographic data and seismic data, allowing for definitive identification of the Subtropical Front and associated water masses in the subsurface. Repeat acquisition along the same transect shows significant temporal variability on the scale of hours, illustrating the highly dynamic nature of this important ocean boundary. Comparisons to conventional low-frequency seismic data in the same location show the value of high-resolution acquisition methods in imaging the near-surface of the ocean and allowing subsurface features to be linked to their expressions at the surface.

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“…continuously map thermohaline structure to the full depth of the water column on a vessel steaming at $5 knots. The frequency characteristic of seismic source and the geometry of the seismic streamer give vertical and horizontal resolutions of about 10 m and it is used to observe variety of ocean phenomena including internal waves, eddies, currents, thermohaline staircases, and turbulence, from mesoscale to finescale in the various global ocean environments [e.g., Nakamura et al, 2006;Biescas et al, 2008Biescas et al, , 2010Fer et al, 2010;Pinheiro et al, 2010;Sheen et al, 2011;Buffett et al, 2013;Holbrook et al, 2013;Tang et al, 2013Tang et al, , 2014a. However, the conventional geometry used for seismic surveying the subseabed makes it difficult to image the near-surface thermohaline structures typically above 200 m because of the minimum offset between the source and receiver array and significant interference from the high-amplitude direct waves [Carniel et al, 2012;Pi et e et al, 2013;Tang et al, 2014b].…”

Section: Introductionmentioning

confidence: 99%

Marine seismic observation of internal solitary wave packets in the northeast South China Sea

et al. 2015

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Recently the novel seismic oceanography method has been reported to be an effective way to study the energetic internal solitary waves (ISWs) in the northern South China Sea. An optimized seismic‐oceanographic cruise was carried out to observe such near‐surface ISWs on Dongsha Plateau in July 2014. Several soliton trains rather than single solitons were captured using the seismic technique. After seismic data processing, one prototypical rank‐ordered ISW packet on northeast side of Dongsha Island was clearly identified for further analysis. This included waveforms, propagation velocities, and vertical velocities for individual solitons. In this study, an improved scheme was applied to derive the transient phase velocities from the seismic data which is verified from independent satellite and hydrographic data. Analytical predictions from Korteweg‐de Vries equation fit better than the extended Korteweg‐de Vries equation ignoring background currents. Our results show that the seismic method can be successfully used to image targets in shallow water below 40 m and that seismic oceanography is a promising technique for studying near‐surface phenomena with high spatial resolution.

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Image of a subsurface current core in the southern South China Sea

Cited by 9 publications

References 37 publications

Seismic observations from a Yakutat eddy in the northern Gulf of Alaska

Seismic observations from a Yakutat eddy in the northern Gulf of Alaska

Temporal Variability of Thermohaline Fine-Structure Associated With the Subtropical Front Off the Southeast Coast of New Zealand in High-Frequency Short-Streamer Multi-Channel Seismic Data

Marine seismic observation of internal solitary wave packets in the northeast South China Sea

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