Diapirism and Faulting, Continental Shelf and Upper Continental Slope Off Southwestern Louisiana

1987 ◽  
pp. 191-223
Keyword(s):  
Continental Shelf ◽  
Continental Slope

scholarly journals Stability of a buoyancy-driven coastal current at the shelf break

2002 ◽  
Vol 452 ◽  
pp. 97-121 ◽  
Author(s):  
C. CENEDESE ◽  
P. F. LINDEN
Keyword(s):  
Continental Shelf ◽  
Continental Slope ◽  
Unstable Mode ◽  
Shelf Break ◽  
Coastal Current ◽  
Surface Currents ◽  
Flat Bottom ◽  
Vertical Boundary ◽  
Axisymmetric Disturbances ◽  
A Current

Buoyancy-driven surface currents were generated in the laboratory by releasing buoyant fluid from a source adjacent to a vertical boundary in a rotating container. Different bottom topographies that simulate both a continental slope and a continental ridge were introduced in the container. The topography modified the flow in comparison with the at bottom case where the current grew in width and depth until it became unstable once to non-axisymmetric disturbances. However, when topography was introduced a second instability of the buoyancy-driven current was observed. The most important parameter describing the flow is the ratio of continental shelf width W to the width L* of the current at the onset of the instability. The values of L* for the first instability, and L*−W for the second instability were not influenced by the topography and were 2–6 times the Rossby radius. Thus, the parameter describing the flow can be expressed as the ratio of the width of the continental shelf to the Rossby radius. When this ratio is larger than 2–6 the second instability was observed on the current front. A continental ridge allowed the disturbance to grow to larger amplitude with formation of eddies and fronts, while a gentle continental slope reduced the growth rate and amplitude of the most unstable mode, when compared to the continental ridge topography. When present, eddies did not separate from the main current, and remained near the shelf break. On the other hand, for the largest values of the Rossby radius the first instability was suppressed and the flow was observed to remain stable. A small but significant variation was found in the wavelength of the first instability, which was smaller for a current over topography than over a flat bottom.

scholarly journals On the occurrence and behaviour of two little-known barnacles, Hexelasma hirsutum and Verruca recta, from the continental slope

1958 ◽  
Vol 37 (3) ◽  
pp. 633-647 ◽  
Author(s):  
A. J. ◽  
Eve C. Southward ◽  
L. H. N. Cooper
Keyword(s):  
Continental Shelf ◽  
Continental Slope ◽  
British Isles ◽  
The South ◽  
South West

The fauna of the continental shelf and slope between Ireland and Spain has been described by Le Danois (1948), but very little faunistic work has been carried out in the area recently. Since R.V. ‘Sarsia’ was brought into service at Plymouth there have been several opportunities of investigating that part of the slope lying to the south-west of the British Isles. It has been found that, in addition to beds of coral, quite extensive exposures of rocks, stones and gravel occur between 200 and 1000 fathoms. There is a rich epifauna in this area and barnacles are one of the dominant groups.

scholarly journals Cascading Over the Continental Slope of Water from the Celtic Sea

1949 ◽  
Vol 28 (3) ◽  
pp. 719-750 ◽  
Author(s):  
L. H. N. Cooper ◽  
David Vaux
Keyword(s):  
Continental Shelf ◽  
Continental Slope ◽  
English Channel ◽  
The South ◽  
Celtic Sea

In the Celtic Sea, to the south of Ireland, water in some winters becomes sufficiently cooled and heavy to flow to the edge of the continental shelf and to run down the continental slope to a depth of several hundred metres. A theory of the phenomenon, termed ‘cascading’, has been developed. Three winters have been examined in detail.In February 1927 much water, heavy enough to cascade, was present in the Celtic Sea and also in the English Channel. A probable course and speed of the cascading water over the shelf has been established. Since there were few observations of salinity and temperature over or beyond the slope, and none of oxygen anywhere, the theory cannot be completely established on the basis of the 1927 observations, full though they were.

scholarly journals Ocean processes at the Antarctic continental slope

2014 ◽  
Vol 372 (2019) ◽  
pp. 20130047 ◽  
Author(s):  
Karen J. Heywood ◽  
Sunke Schmidtko ◽  
Céline Heuzé ◽  
Jan Kaiser ◽  
Timothy D. Jickells ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Continental Shelf ◽  
Continental Slope ◽  
Climate Models ◽  
Water Mass ◽  
Ocean Model ◽  
Shelf Break ◽  
Small Scale ◽  
Exchange Processes ◽  
The Antarctic

The Antarctic continental shelves and slopes occupy relatively small areas, but, nevertheless, are important for global climate, biogeochemical cycling and ecosystem functioning. Processes of water mass transformation through sea ice formation/melting and ocean–atmosphere interaction are key to the formation of deep and bottom waters as well as determining the heat flux beneath ice shelves. Climate models, however, struggle to capture these physical processes and are unable to reproduce water mass properties of the region. Dynamics at the continental slope are key for correctly modelling climate, yet their small spatial scale presents challenges both for ocean modelling and for observational studies. Cross-slope exchange processes are also vital for the flux of nutrients such as iron from the continental shelf into the mixed layer of the Southern Ocean. An iron-cycling model embedded in an eddy-permitting ocean model reveals the importance of sedimentary iron in fertilizing parts of the Southern Ocean. Ocean gliders play a key role in improving our ability to observe and understand these small-scale processes at the continental shelf break. The Gliders: Excellent New Tools for Observing the Ocean (GENTOO) project deployed three Seagliders for up to two months in early 2012 to sample the water to the east of the Antarctic Peninsula in unprecedented temporal and spatial detail. The glider data resolve small-scale exchange processes across the shelf-break front (the Antarctic Slope Front) and the front's biogeochemical signature. GENTOO demonstrated the capability of ocean gliders to play a key role in a future multi-disciplinary Southern Ocean observing system.

Geology of the Western Approaches of the English Channel: a progress report

1962 ◽  
Vol 265 (1322) ◽  
pp. 395-406 ◽  
Keyword(s):  
Continental Shelf ◽  
Continental Slope ◽  
Progress Report ◽  
English Channel ◽  
Rock Outcrops ◽  
Logical Approach ◽  
Sea Bed ◽  
Westerly Direction ◽  
Sand And Gravel

Eight short cruises over the last 3 years, each of from 1 to 3 weeks’ duration in either R.V. Sarsia or R.R.S. Discovery II , were specially planned having regard to some of the geological and allied problems which could be expected in the Western Approaches leading out to the edge of the continental shelf, and hence to the upper parts of the continental slope. Fourteen scientists have so far participated in one or more of these cruises, mainly geologists and engineers. The primary geological objective is to try and arrive at an explanation of the origin of the continental slope, which will necessarily involve the origin of the adjacent continental shelf. To a geologist, the logical approach to the problems is, first, to determine the geological sequences in the shelf and, secondly, thus to extend the shallow structures and successions determined there to the upper reaches of the slope. The thin cover of a few inches of sand and gravel which normally occurs on the sea bed of the English Channel will almost certainly become too thick in a westerly direction for penetration by those coring methods which are at present available, and the most promising methods by means of which the established geology of the Western Approaches will be connected with the upper ranges of the continental slope are, first, the thumper and sparker techniques and, secondly, dredging from rock outcrops now known to occur on the slope. Such an orthodox geological approach demands progress pari passu from east to west. Our provisional results, of which progress reports follow, are thus mainly, but not entirely, concerned with the Western Approaches west of longitude 4° W.

scholarly journals The East Australian Current, upwellings and downwellings off eastern-most Australia in summer

2017 ◽  
Vol 68 (7) ◽  
pp. 1208 ◽  
Author(s):  
G. R. Cresswell ◽  
J. L. Peterson ◽  
L. F. Pender
Keyword(s):  
Continental Shelf ◽  
Continental Slope ◽  
Wind Stress ◽  
Satellite Images ◽  
East Australian Current ◽  
Inner Shelf ◽  
Per Se ◽  
Flowing Stream ◽  
Inner Continental Shelf ◽  
Upper Slope

The complex influences of the East Australian Current (EAC) and winds on the waters of the continental shelf were addressed with a ship survey, moored and drifting instruments, satellite images and wind and sea level measurements. The study revealed intrusions of continental slope water reaching the inner continental shelf when the EAC was near the shelf edge and wind stress was near zero or upwelling favourable (northerly). The process was the onshore movement of a southward flowing stream of water originally from the continental slope. One event was captured near Cape Byron and Evans Head when these waters upwelled to the surface. When the wind stress turned northward, it reversed the inner shelf current and drove downwelling. Variations in the wind stress also modulated the strength of the EAC out across the shelf to the upper slope. The strength of the EAC per se varied with a time scale of 2–3 months; these variations decreased in amplitude westward until they were undetectable at the inner shelf. The EAC had a subsurface speed maximum of up to 1.6ms–1 at 100–150-m depth above the continental slope and was seen to accelerate with both time and distance southward along the 190-km length surveyed by the ship.

scholarly journals Land to Ocean Transfer of Erosion-Related Organic Carbon, Waipaoa Sedimentary System, East Coast, New Zealand

2021 ◽  
Author(s):  
◽  
Hannah Lema Brackley
Keyword(s):  
New Zealand ◽  
Organic Carbon ◽  
Continental Shelf ◽  
Continental Slope ◽  
East Coast ◽  
Thick Layer ◽  
Terrestrial Source ◽  
The Pacific ◽  
The Pacific Ocean ◽  
Floodplain Sediments

<p>Mountainous islands of the Pacific Rim (such as New Zealand) purportedly deliver up to 40% of the suspended sediment load and up to 35% of the riverine particulate organic carbon (POC) load to the world's oceans. On the east coast of New Zealand's North Island, the Waipaoa River drains a steep, 2205 km2 catchment located on the active collisional East Coast Continental Margin. It has an annual suspended sediment load of 15 Tg (15 x 1012 g), making up ~7% of New Zealand's total yield to the Pacific Ocean, and a mean annual POC discharge to the Pacific Ocean of 86.7 Gg (86.7 x 109 g). The annual loss of OC to the floodplain is ~9% of this annual POC discharge (~7.8 Gg). A range of analyses (including organic carbon content (%OC), stable carbon isotopes (Delta 13C), radiocarbon (14C), carbon to nitrogen ratios (C/N)a and carbon loadings (OC:SA)) were performed on correlative sediments from a transect of 7 cores from depositional sites located on the Waipaoa River floodplain and adjacent continental shelf and slope. Results were used to determine biogeochemical characteristics of organic carbon (OC) at a range of depositional sites during its transfer from terrestrial source to marine sink, and how large floods impact OC transfer to the marine environment. The high temporal variability in OC content (0.2 to 3.5%) and different source signatures (Delta 13C of -26.7 to -20.6% degrees) of Waipaoa River floodplain deposits prevented the establishment of a clear benchmark signature for flood deposits that may be recognisable in the marine sedimentary record. The high spatial and temporal variability of floodplain sediment OC, combined with the areal extent of floodplains within the catchment, indicates the appreciable modulating effect the floodplain has on OC transfers to the ocean. Since extensive stopbanks were constructed on the main floodplain since the 1940' s, sequestration of OC in floodplain sediments has reduced by about half, increasing the overall efficiency of the Waipaoa River in transferring terrestrial OC directly to the marine environment.  Flood layers are preserved in the marine sedimentary record. Continental shelf sediments indicate that during Cyclone Bola (March 1988, a rainfall event with a >100 year return period), the extreme river discharge produced a hyperpycnal (negatively buoyant) plume, preserved as a ~10 cm thick layer on the inner shelf and a ~1 cm thick layer on the mid-shelf. The flood layer contains a significant amount of terrestrially-sourced OC (up to 86% of total OC in >25 Mu m fraction) which subsequently was rapidly buried by normal marine deposits (in which ~60% of OC in >25 Mu m fraction is terrestrial), thereby preserving its strong terrestrial source signature. As sediments are physically and biologically processed at various depositional sites across the continental shelf and slope, they lose some of their modern terrestrial OC, and the concurrent addition of marine sourced OC results in the sediments gaining a stronger marine biogeochemical signature (Delta 13C values increasing from -26.2% degrees for floodplain sediments to -21.6% degrees for upper continental slope sediments). Carbon loading (OC:SA) and 14C data revealed the contributions of kerogen, modern terrestrial OC and modern marine OC to the total OC of continental shelf and slope surface sediments. Sediments retain about 40% of their terrestrial OC following transport to the continental slope, of which a significant amount consists of kerogen. Because of high erosion rates within the catchment, kerogen associated with the particles escapes oxidation, and therefore makes up a large part of the POC flux. Kerogen is preserved across the margin to the mid-slope, where only 8% of the bulk sediment OC consists of modern terrestrial OC, 58% is modern marine OC and 34% is kerogen. Biomarker analyses of surface samples also support findings that terrestrial OC is being transferred across the continental margin, with plant sterols, long chain alcohols and long chain fatty acids (biomarkers indicative of vascular plants) persisting as far offshore as the mid-continental slope. Results presented verify and add to the understanding of OC transfers and transformations at a range of depositional sites from terrestrial source to marine sink. This study provides the first quantitative assessment of land to ocean OC transfers from New Zealand. These findings, together with information on sediment budgets and depositional rates of OC in terrestrial and marine depositional environments, could provide a vital step toward establishing global OC budgets for small mountainous island environments.</p>

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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