scholarly journals Observation of the Relationship between Ocean Bathymetry and Acoustic Bearing-Time Record Patterns Acquired during a Reverberation Experiment in the Southwestern Continental Margin of the Ulleung Basin, Korea

2021 ◽  
Vol 9 (11) ◽  
pp. 1259
Author(s):  
Youngcheol Jung ◽  
Keunhwa Lee
Keyword(s):  
Continental Slope ◽  
Continental Margin ◽  
Ulleung Basin ◽  
Variable Depth ◽  
Soft Bottom ◽  
Continuous Waves ◽  
Time Record ◽  
Towed Array ◽  
The Relationship ◽  
Acoustic Reverberation

We observed a distinct drop-off region in the bearing-time record of acoustic reverberation data acquired from the south-western continental margin of the Ulleung Basin, East Sea, in the summer of 2015. 3 kHz continuous waves with pulse lengths of 0.1, 0.3, and 1.0 s were used as source pulses, with an R/V Cheonghae vessel towing a variable depth source and a triplet towed array toward the deep sea from shallow water. The observed pattern changed as the R/V Cheonghae moved across the continental slope further into the sea. This pattern arises as a result of the downward-refracted beams in the 1/2 convergence zone interacting with the soft bottom. In addition, the boundary of the drop-off region was modeled with the two-way maximum travel time of the first bottom-reflected rays using the bathymetry model of the General Bathymetric Chart of the Oceans, 2020. Some discrepancies were observed when comparing the modeled curve to the measured results, and the inaccuracy of the bathymetry model on the continental slope could be the main cause of these discrepancies. This pattern could be useful for bathymetry mapping, as well as estimations of source and receiver configurations.

Currents off south-eastern Australia: results from the Australian coastal experiment

1988 ◽  
Vol 39 (3) ◽  
pp. 245 ◽  
Author(s):  
A Huyer ◽  
RL Smith ◽  
PJ Stabeno ◽  
JA Church ◽  
NJ White
Keyword(s):  
Sea Level ◽  
Continental Slope ◽  
Wind Stress ◽  
Continental Margin ◽  
Eddy Currents ◽  
Empirical Orthogonal Functions ◽  
Trapped Waves ◽  
Orthogonal Functions ◽  
Coastal Trapped Waves ◽  
And Sea Level

The Australian Coastal Experiment was conducted off the east coast of New South Wales between September 1983 and March 1984. The experiment was conducted with arrays of current meters spanning the continental margin at three latitudes (37.5�, 34.5�, and 33.0�S.), additional shelf moorings at 29� and 42�S. coastal wind and sea-level measurements, monthly conductivity-temperature-depth probe/expendable bathythermograph (CTD/XBT) surveys, and two satellite-tracked buoys. Over the continental shelf and slope, the alongshore component of the current generally exceeded the onshore component, and the subtidal (<0.6 cpd, cycles per day) current variability greatly exceeded the mean flow. Part of the current variability was associated with two separate warm-core eddies that approached the coast, causing strong (>50 cm sec-1), persistent (>8 days), southward currents over the continental slope and outer shelf. Temperature and geostrophic velocity sections through the eddies, maps of ship's drift vectors and temperature contours at 250 m, and the satellite-tracked drifter trajectories showed that these eddies were similar in structure to those observed previously in the East Australian Current region. Both eddies migrated generally southward. Eddy currents over the shelf and slope were rare at Cape Howe (37.5�S.), more common near Sydney (34.5�S.), and frequent at Newcastle (33.0�S.), where strong northward currents were also observed. Near Sydney, the eddy currents over the slope turned clockwise with depth between 280 and 740 m, suggesting net downwelling there. Repeated CTD sections also indicated onshore transport and downwelling at shallower levels; presumably, upwelling occurred farther south where the eddy currents turned offshore. Periodic rotary currents over the continental slope near Sydney and Newcastle indicated the presence of small cyclonic eddies on the flank of a much larger anticyclonic eddy. Between early October and late January, no strong southward currents were observed over the continental margin near Sydney. Data from this 'eddy-free' period were analysed further to examine the structure and variability of the coastal currents. Much of this variability was correlated with fluctuations in coastal sea-level (at zero lag) and with the wind stress (at various lags). The coherence and phase relationships among current, wind-stress, and sea-level records at different latitudes (determined from spectral analysis and frequency-domain empirical orthogonal functions) were consistent with the equatorward propagation of coastal-trapped waves generated by winds in phase with those near Cape Howe. Time-domain empirical orthogonal functions show that the current fluctuations decayed with distance from shore and with depth, as expected of coastal-trapped waves.

Geophysical evidence and inferred triggering factors of submarine landslides on the western continental margin of the Ulleung Basin, East Sea

2016 ◽  
Vol 36 (6) ◽  
pp. 425-444 ◽  
Author(s):  
Deniz Cukur ◽  
Seong-Pil Kim ◽  
Gee-Soo Kong ◽  
Jang-Jun Bahk ◽  
Senay Horozal ◽  
...  
Keyword(s):  
Continental Margin ◽  
East Sea ◽  
Ulleung Basin ◽  
Submarine Landslides ◽  
Triggering Factors

scholarly journals GEOMORPHOLOGICAL AND SEDIMENTOLOGICAL CHARACTERIZATION OF THE URUGUAYAN CONTINENTAL MARGIN: A REVIEW AND STATE OF ART / CARACTERIZAÇÃO GEOMORFOLÓGICA E SEDIMENTOLÓGICA DA MARGEM CONTINENTAL DO URUGUAI: UMA REVISÃO E ESTADO DA ARTE

2018 ◽  
Vol 3 (4) ◽  
pp. 253-264 ◽  
Author(s):  
Leticia Burone ◽  
Paula Franco-Fraguas ◽  
Michel Mahiques ◽  
Leonardo Ortega
Keyword(s):  
Continental Shelf ◽  
Continental Slope ◽  
Continental Margin ◽  
Global Climate ◽  
Rio De La Plata ◽  
Río De La Plata ◽  
Southwest Atlantic ◽  
La Plata ◽  
Deep Circulation

The Uruguayan Continental Margin is located in a strategic location of great relevance to understand the dynamics of the regional and global climate and to study the sedimentary processes. The Río de la Plata represents the largest fluvial discharge of the Southwest Atlantic (23.000 m3/s of water and 57.000.000 m3/year of sediment for the South Atlantic Ocean). The sub-surface and deep circulation are characterized by the confluence of water masses with contrasting thermohaline characteristics that determine the formation of well-marked hydrological fronts. In the continental shelf, this characteristic is represented by the Subtropical Shelf Front, as a shallow extension of the Brazil-Malvinas Confluence that occurs in deep water off the shelf. Although the knowledge of the regional circulation is acceptable, there are significant gaps in the knowledge related to the influence of this complex hydrological system on sedimentation processes. The objective of this work is to synthesize the present knowledge about the morpho-sedimentary characteristics of the Uruguayan Continental Margin and the processes involved in its formation. It also aims to discuss some knowledge gaps that are the subject of current research in the region. The knowledge reflects the scientific-technological evolution at a global level that is translated in the increase of recent works on the continental slope. Nowadays, most of the available information is associated with the inner shelf and upper slope. Starting from the basis of the close relationship between bathymetry and sedimentological distribution it is clear that efforts should be concentrated on the better understanding of the interaction between the shelf and the slope. The scientific knowledge regarding sedimentology and geochemistry along the Uruguayan Continental Margin is still, scarce and heterogeneous. However, it indicates complexity in the sedimentary coverture present both in the continental shelf and slope. The Uruguayan Continental Margin can be considered as an in situ laboratory to improve the understanding of the influence of oceanic hydrodynamics on the margin configuration, a key point to achieve better paleoceanographic interpretations. In this sense, due to the complexity of both modern hydrology and morphological configuration of the margin, it would be interesting to understand the relative importance of the control of each environment on surface sedimentation. A better understanding of the processes that link the near bottom circulation and continental slope features is needed. At the same time, this will allow deepening a new field of research in Uruguay, considering the joint and interrelated vision between sedimentary and oceanographic processes. ResumoA Margem Continental do Uruguai está localizada num local estratégico de grande relevância para entender a dinâmica do clima regional e global e para estudar os processos sedimentares. O Río de la Plata representa a maior descarga fluvial do Atlântico Sudoeste (23.000 m3/s de água e 57.000.000 m3/ano de sedimento para o Oceano Atlântico Sul). A circulação de subsuperfície e profunda são caracterizadas pela confluência de massas de água com características termohalinas contrastantes que determinam a formação de frentes hidrográficas bem marcadas. Na plataforma continental, essa característica é representada pela Frente Subtropical da Plataforma, uma extensão rasa da Confluência Brasil-Malvinas que ocorre em águas profundas ao largo da plataforma. Embora seja considerável o conhecimento da circulação regional, existem lacunas significativas no conhecimento da influência deste complexo sistema hidrológico nos processos de sedimentação. O objetivo deste trabalho é sintetizar o conhecimento atual sobre as características morfo-sedimentares da Margem Continental Uruguaia e os processos envolvidos na sua formação. Também pretende discutir algumas lacunas de conhecimento que são objeto de pesquisas atuais na região. O conhecimento reflete a evolução científico-tecnológica a nível global, que se traduz no aumento de trabalhos recentes na vertente continental. Atualmente, a maior parte da informação disponível está associada à plataforma continental interna e ao talude continental superior. Partindo da base da estreita relação entre a batimetria e a distribuição sedimentológica, torna-se claro que os esforços devem ser concentrados na melhor compreensão da interação entre a plataforma e o talude continental. O conhecimento científico sobre sedimentologia e geoquímica ao longo da Margem Continental do Uruguai é ainda escasso e heterogêneo. No entanto, os dados existentes indicam que a cobertura sedimentar presente tanto na plataforma quanto no talude continental é complexa. A Margem Continental do Uruguai pode ser considerada um laboratório in situ para melhorar a compreensão da influência da hidrodinâmica oceânica na configuração da margem, ponto chave para se obterem melhores interpretações paleoceanográficas. Nesse sentido, devido à complexidade da hidrologia moderna e da configuração morfológica da margem, seria interessante entender a importância relativa do controle de cada ambiente sobre a sedimentação superficial. É necessário um melhor entendimento dos processos que ligam as características de circulação próxima do continente à que ocorre no talude continental. Este conhecimento permitirá aprofundar um novo campo de pesquisa no Uruguai, considerando a visão conjunta e inter-relacionada entre processos sedimentares e oceanográficos. 

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