Submarine Canyons

Shelf break systems are ecologically important regions of the ocean, and are often characterized by enhanced productivity and high densities of species from lower to upper trophic levels. Along with associated submarine canyons, shelf break regions provide important foraging habitat for deep-diving odontocetes such as pilot whales. Short-finned pilot whales Globicephala macrorhynchus are found throughout tropical and subtropical waters, but there is little information on the habitat use of this species in the northwest Atlantic. We examined the movements and foraging behavior of short-finned pilot whales using data from satellite tags (n = 33) deployed off Cape Hatteras, North Carolina, USA in 2014 and 2015. Pilot whale tracks ranged from Cape Lookout, North Carolina north to Georges Bank, with movements and habitat use primarily focused north of Cape Hatteras. We observed 2 distinct modes of behavior, with most pilot whales showing a strong affinity for the continental shelf break and others following offshore meanders of the Gulf Stream for all or part of the observed track. We used first passage time (FPT) to assess area-restricted search behavior, and found that FPT was significantly higher close to the shelf break and in submarine canyons. Our results demonstrate the importance of steep bathymetric features to the foraging habitat and distribution of short-finned pilot whales in this region. In addition, our findings suggest that pilot whales in the Mid-Atlantic Bight may have developed specialized foraging behaviors for targeting steep bathymetric gradients, and that their latitudinal distribution may be limited to regions where this foraging strategy is effective.

Os cabos submarinos de fibra óptica e os satélites de comunicações – representação e desconstruções. Curiosamente, e apesar da sua enorme e crescente importância para comunicações contemporâneas de inúmeros tipos, os cabos de fibras ópticas, e sobretudo os cabos submarinos de entre os quais são de sublinhar os que ligam entre si as costas litorais das bacias oceânicas e marítimas – e a partir daí os interiores das massas continentais – não têm nem por sombras recebido a atenção pública e/ou académica que merecem. Como tantas vezes é o caso ao abordarmos questões tecnológicas, as representações espontâneas da importância que lhes atribuímos são enganadoras: talvez em resposta à publicitação das corridas ao espaço encetadas pelo Sputniks soviéticos, no quadro de uma corrida espacial que se prolongou pela Guerra Fria adentro, culiminando com a vitória norte-americana com o seu pico na alunagem do módulo Eagle da Apollo 11, a 20 de Julho de 19692. Uma vitória acompanhada e depois seguida por um número cada vez maior de objectos colocados em órbita para garantir melhores comunicações bem como missões espaciais de todo o tipo que vemos crescer vertiginosamente, levadas a cabo pela Rússia, pelo Japão, pela União Europeia, pela Índia, pela China, entre vários outros, supostamente criando redes físicas de suporte tecnológico que servem de garante para as nossas comunicações. No entanto, esse suporte tecnológico não está no espaço, acima, mas antes nos fundos marítimos e oceânicos. Vários actos relevantes há que falam por si na desconstrução deste mito. Segundo dados, relativos a 2016, fornecidos pela US Federal Communications Commission, apenas 0,37% da capacidade norte-americana para estabelecer comunicações com o exterior depende de satélites. Ou seja, virtualmente toda essa capacidade corre nos cabos submarinos3. No resto do mundo a situação não é muito diferente, com excepção, claro está, para os Estados ditos " encravados " , a saber, sem costa (que também usam cabos de fibra óptica, mas terrestre). Tem sido através deles que passam as comunicações áudio e vídeo de telecoms variados, todo o tipo de operadores móveis, Estados e empresas transnacionais, motores de busca, fornecedores de dados, bancos e banca, i.e. informação e instruções relacionadas com investimentos públicos e privados. Neste artigo abordo a importância da centralidade crescente de Portugal na rede global de cabos, nas suas diversas fases e com as suas dificuldades e vantagens próprias.

The aim of this study is to assess the global occurrence of large submarine canyons to provide context and
guidance for discussions regarding canyon occurrence, distribution, geological and oceanographic significance
and conservation. Based on an analysis of the ETOPO1 data set, this study has compiled the first inventory of
5849 separate large submarine canyons in the world ocean. Active continental margins contain 15% more
canyons (2586, equal to 44.2% of all canyons) than passive margins (2244, equal to 38.4%) and the canyons are
steeper, shorter, more dendritic and more closely spaced on active than on passive continental margins. This
study confirms observations of earlier workers that a relationship exists between canyon slope and canyon
spacing (increased canyon slope correlates with closer canyon spacing). The greatest canyon spacing occurs in
the Arctic and the Antarctic whereas canyons are more closely spaced in the Mediterranean than in other
areas.
River-associated, shelf-incising canyons are more numerous on active continental margins (n=119) than on
passive margins (n=34). They are most common on the western margins of South and North America where
they comprise 11.7% and 8.6% of canyons respectively, but are absent from the margins of Australia and
Antarctica. Geographic areas having relatively high rates of sediment export to continental margins, from
either glacial or fluvial sources operating over geologic timescales, have greater numbers of shelf-incising
canyons than geographic areas having relatively low rates of sediment export to continental margins. This
observation is consistent with the origins of some canyons being related to erosive turbidity flows derived
from fluvial and shelf sediment sources.
Other workers have shown that benthic ecosystems in shelf-incising canyons contain greater diversity and
biomass than non-incising canyons, and that ecosystems located above 1500 m water depth are more
vulnerable to destructive fishing practices (bottom trawling) and ocean acidification caused by anthropogenic
climate change. The present study provides the means to assess the relative significance of canyons located in
different geographic regions. On this basis, the importance of conservation for submarine canyon ecosystems
is greater for Australia, islands and northeast Asia than for other regions.

Executive Summary

Geoscientific contributions to infrastructural development in the Geologically hazardous coastal environment at Lae in Papua New Guinea, are the subject of this joint Geological Survey of Papua New Guinea (GSPNG) / Coastal and Offshore Geoscience in East and South East Asia (CCOP) COASTPLAN study.  The study of Natural Hazards in Lae, Papua New Guinea addresses the geological hazards that hinder the physical and economic growth of Papua New Guinea’s principal port and second city. 

Lae lies under the shadow of the Finisterre-Sarawaget range a steep and rugged range of mountains rising over 4000 metres and being pushed continually upwards by a collision between two major tectonic plates. This collision which involves both components of compression and strike-slip is the driving force and in many cases the triggering mechanism for a whole suite of geological hazards.  These hazards not only effect the city of Lae but the communication links with the important highlands region.

The CCOP COASTPLAN project demonstrates that geoscience has an essential role in planning and management of rapidly developing coastal areas. This study, one of three undertaken in East and Southeast Asia, considers the risks to people and property, and the constraints to development, from dangerous and damaging natural events, such as earthquakes, floods, landslides, tsunamis and coastal erosion. It has been a 15 month project, with COASTPLAN support of about $US 200,000.  The study has been undertaken by geoscientists at Geological Survey of Papua New Guinea, assisted by special advisors. 

The project activities have included:
• data compilation
• new data acquisition
• technology transfer and capacity building
• information synthesis, identification of    knowledge gaps
• recommendations for future action to further define and reduce or mitigate risk. 

Recommendations for future activities to better understand and minimize the risks associated with each type of hazard include some of the following:

• Earthquakes – carry out a detailed field survey of sediment and foundation conditions in Lae and surroundings to identify locations vulnerable to earthquake – microzonation, induced liquefaction and slope failure.

• Floods – conduct an airborne video survey of the Markham, Butibum and Busu floodplains using state of the art methods as a new database for flood vulnerability assessment

• Coastal land loss – reconstruct coastline behavior, past and present, and  large scale erosion / sedimentation patterns from historical data

• Landslides – Carry out an assessment of landslide hazard potential in the Atzera range and magnitude-frequency studies for landslide induced flood events in the Busu and other major river valleys.  Landslide induced flooding has destroyed 5 bridges in the region since 1993 yet engineers continue to design bridges based on much smaller rainfall flood events

• Submarine processes - measure the geotechnical properties of offshore sediments in situ in offshore boreholes in order to determine the potential for renewed slope failure under various conditions

• Tsunamis – conduct field surveys to accurately locate potential inundation areas from different magnitude waves.  It is perceived that many thousands of people in the coastal settlements and villages around Lae may be at risk

In the preparation of this report it has become apparent that a detailed, comprehensive hazard zonation map of the Lae area is absolutely essential.

• Hazard Map - The single most important recommendation is that a detailed map of the city and its surroundings is required. It should show elevation contours, slope angles, sediment types and properties, liquefaction and slope instability potential, floodplain limits, river channels, river erosion sites and coastal erosion and accretion sites and would provide basic information that would be useful to many people. The map would be zoned to indicate the key infrastructure and population centres that are vulnerable to different hazards as well as those areas are least vulnerable and therefore more suitable for future development. Two versions of the geological hazard  map should be prepared – one using technical language and terms, aimed at planners and engineers: the another in plain language aimed directly the people of Lae, to improve their understanding and emergency response. A Tok Pisin version, the local Lingua Franca could also be published.

A suite of seep samples from the vicinity of the Marco Polo field in the Green Canyon area of the Gulf of Mexico provides an exceptional opportunity to study the impact of interference from sediment background organic matter and alteration by biodegradation on thermogenic hydrocarbons from seafloor seeps. These seep samples contain a range in both the concentration of seeped hydrocarbons present and level of biodegradation experienced. In addition, the subsurface oil that sources the seepage was available for comparison.

In the framework of the Vulnerable Marine Ecosystems (VME) of the High Seas of the South West Atlantic, large areas of the Argentine Continental Margin (ACM) between 44º30'S and 48ºS have been swath-mapped for the first time, obtaining full data coverage of the seafloor in this region between the outermost continental shelf and the middle slope down to 1600 m water depth. The slope is characterized by the presence of smooth terraces (Nagera, Perito Moreno and Piedra Buena) that widen towards the south, limited by morphological steps with evident signs of erosion in the form of scours. These terraces form part of the Argentine contourite depositional systems, generated by the interaction of the northwards flowing Antarctic water masses with the seafloor. Within the studied area, seven canyons and their multiple branches dissect the upper and middle continental slopes, from west to east, across the terraces and the steps. These canyons, which belong to the Patagonia submarine canyon system and are collected at a depth of ~3.5 km by a slope-parallel, SSW-NNE-oriented channel known as the Almirante Brown transverse canyon, display a large variety of morphologies.

To date, facies architecture models of submarine channel–levees have largely been derived from seismic data, isolated core data and limited field studies. We report field observations of an Upper Cretaceous submarine channel–levee complex within the Rosario Formation, Baja California, Mexico, which provide high-resolution data of lithofacies and ichnofacies distribution, and levee depositional thickness decay along transects perpendicular to the channel axis. Within the levee, both sandstone thickness and the overall proportion of sandstone decrease according to a power law away from the channel axis. Spatial variation in sedimentary structures away from the channel axis is predictable and provides an important link to the depositional flow regime. In channel-proximal locations, structureless sands, parallel lamination, overturned ripples, and ripple cross-lamination (including climbing ripple cross-lamination) are common; in channel-distal localities starved ripples are abundant. Sandstone bed thickness generally increases up stratigraphy within the levee succession, which is interpreted to indicate increasing turbidity current magnitude and/or contemporaneous channel floor aggradation reducing relative levee relief. However, in the most channel-proximal location sandstone bed thickness decreases with height; combined with evidence from both facies and palaeocurrent analysis this allows the position of the levee crest to be inferred. The thickest beds occur at higher levels with increasing distance from the channel axis, using this evidence we present a model for levee growth and migration of the crest.Quantitative analysis of ichnofacies distribution reveals that traces typical of the Cruziana and Skolithos ichnofacies are superimposed over the ‘normal’ background Nereites ichnofacies, forming a ‘bioturbation front’ which is indicative of proximity to the channel. By analogy with modern canyons and channels, the association of Cruziana and Skolithos ichnofacies with the channel may be attributed to oxygen and nutrient enrichment and possible turbidity current transport of organisms responsible for these ichnofacies.

This study examines the accuracy of the predictions of gas hydrate saturations made based on five-step analysis of 3D seismic data prior to 2005 drilling, logging, conventional coring, and pressure core sampling through the gas hydrate stability zone at two focus sites in the northern Gulf of Mexico. These predictions are detailed in Part I (2008). Here we conduct a detailed analysis of the gas hydrate saturation using both resistivity and P-wave velocity log data and analyze the pre-drilling predictions, which were made almost exclusively on the basis of seismic data, with no local logging control. Well log measurements, core data analysis, and pressure core-degas experiments all indicated general agreement with the pre-cruise analysis regarding the location and approximate concentration of gas hydrates in the sediments. We find that seismic predictions are generally consistent with log-based estimates after upscaling to seismic frequencies. We recalibrated the pre-drill model based on the new field data so that a refined version of the model could be used for future work.

The seascape of the continental shelf and slope offshore Santa Marta is sculpted by the submarine Aguja
Canyon, a deep seafloor incision that extends from the inner shelf to the continental rise along some
115 km. No major modern rivers flow into this canyon, thus ruling out principal fluvial control on the
present geometry of this feature. Recently acquired multibeam sonar bathymetry data have provided
insight into the three-dimensional geometry of this outstanding feature that disrupts the seafloor relief.
In addition, seismic reflection data provide images of the internal structure of the canyon’s subsurface. In
this study, we describe the morphology of the Aguja Canyon along a series of transects, interpret the
structure under the canyon, and discuss possible geologic processes that played a role during its formation
and modification. Seismic data indicate that incision of the canyon’s inner reach is the result of
recent motion along the western termination of the active Oca strike–slip fault. Relief in the middle reach
may be predominantly controlled by sedimentary processes (erosion, infilling and lateral thalweg migration).
In the past, however, the middle reach may have been tectonically controlled. The outer reach
appears to be the combined result of tectonics, sedimentary process and mud-diapiric intrusions. We
conclude that the Aguja Canyon is predominantly a tectonic feature that accommodates shallow transpressive
stresses as dislocation of the seafloor.

Several laterally offset and aggradational sinuous submarine channels are contained within a 54 km long segment of the Benin-major Canyon. Axial channel deposits produce high amplitude reflections on three-dimensional (3-D) seismic profiles. Some seismic reflections have U- or V-shaped cross-sectional motifs that were correlated with confidence along linear to meandering paths for distances up to 70 km. They are referred to here as channel-forms (CFs), and are believed to be the axial parts of submarine channels preserved during overall channel floor aggradation. A total of 15 separate CFs were mapped allowing thalweg-gradients, dimensions, and morphology to be studied spatially and through time, providing insight into how submarine canyons fill. Their planform geometry evolved predominantly in a stepwise fashion through alternating periods of cut-and-fill, but more gradual channel migrations are also observed. The largest offsets in successive channel floor position occur after periods of significant vertical CF fill (‘thalweg plugging’—with deposits commonly consisting of lower amplitude, transparent to chaotic seismic reflections). The passage of erosive flows after such periods of fill caused abrupt shifts in channel position, particularly at meander bends, with increased potential for the formation of pseudo meander loop cut-offs. Significant spatial differences in the stacking architecture of CFs are attributed to local slope deformation and perhaps also to a recent channel avulsion just west of the study area. Abrupt channel straightening in the western study area coincides with a period of increased valley-gradient associated with amplification of an underlying anticlinal fold. The youngest CFs in this area show limited aggradation and are characterized by repeated episodes of headward erosion causing knickpoint migration as the recent channel floor tried, unsuccessfully, to establish a smooth graded depth profile. This is in stark contrast to the time-equivalent predominantly aggradational CFs in the eastern study area that show a progressive increase in sinuosity through time.

The modern Bass Canyon is one of the world's largest submarine canyon systems that is entirely located within a cool-water
carbonate environment. Five large shelf-breaching and three slope-confined tributary canyons coalesce on the lower slope and enter
the massive deep-water Bass Canyon at 3000 m depth. Normal slope sediments consist predominantly of sandy calcilutite and
muddy calcarenite interpreted as mud flow and mud-lubricated sandy debris flow deposits respectively, and hemipelagic
foraminiferal calcilutite. Canyon head sediments consist of intraclast-rich calcarenite and calcirudite, probably deposited by masswasting
events, and fine calcarenite, deposited by cohesionless sandy debris flows. Canyon filling sediments consist of well-sorted
fine calcarenite deposited by (long term) semi-continuous cohesionless sandy debris flows, and rarer intraclast-rich mud,
interpreted as cohesive sediment gravity flow deposits. Two types of tributary canyons are recognized: V-shaped canyons with
steep walls (up to 35°) that are well-defined by backscatter acoustics; and broad U-shaped canyons (walls≤10°) poorly defined by
backscatter. It is most likely that tributary canyons developed from down-slope eroding sediment gravity flows triggered at the
shelf break, which mature to develop dendritic canyon heads. Dendritic canyon heads entrain coarse-grained shelf sediment, which
fuel erosive gravity flows and scour deep V-shaped canyon profiles. Once canyon heads stabilise, shelf-derived erosive sediment
flows are reduced and the canyon profile switches from V- to U-shaped. This is aided by continual pelagic sedimentation and
sediment gravity flows from the adjacent slope and canyon walls. Mud-free sandy debris flows from the lower slope converge with
sandy outflows from tributary canyons and flow down the Bass Canyon floor. Sand cored from the Bass Canyon floor preserves
cyclic fluctuations in magnetic susceptibility. High magnetic susceptibility zones are associated with increases in cool-temperature
planktonic foraminiferal, and have been tentatively correlated to oxygen isotope stages 6.2–6.8 (135–185 ka) and 8.2–8.4 (245–
278 ka). Based on this correlation, sedimentation rates on the slope and within the Bass Canyon were found to be highest during the highstand and regressive systems tracts, and lowest during the lowstand and transgressive systems tracts.

Use of deep‐water sediments in submarine fans to reconstruct changing erosion onshore is based on the premise of relatively simple transport between source and sink. However, debate continues regarding the degree of sediment buffering and recycling in the sediment transport process. In this study, we investigate the origin of sediment in the Indus Submarine Canyon since the Last Glacial Maximum (LGM; ~20 ka) using zircon U‐Pb dates. Zircon grains in the submarine canyon are resolvably different from those at the river mouth, at least before 6.6 ka, implying a disconnection between the river mouth and the canyon up to that time. Sand may be stored near the river mouth as sea level rose, while finer‐grained sediment was directly transferred into deeper water. Since 1 ka the upper canyon has shown big and rapid provenance changes, most notably a sharp increase in erosion from Nanga Parbat, whose influence is minor in the modern river. Such rapid changes imply a lack of buffering in the recent past. The modern river contrasts with sediments in the canyon in terms of its zircon U‐Pb age populations and may be influenced by significant anthropogenic impact on the terrestrial drainage basin, especially damming.

This study examines the accuracy of the predictions of gas hydrate saturations made based on five-step analysis of 3D seismic data prior to 2005 drilling, logging, conventional coring, and pressure core sampling through the gas hydrate stability zone at two focus sites in the northern Gulf of Mexico. These predictions are detailed in Part I (2008). Here we conduct a detailed analysis of the gas hydrate saturation using both resistivity and P-wave velocity log data and analyze the pre-drilling predictions, which were made almost exclusively on the basis of seismic data, with no local logging control. Well log measurements, core data analysis, and pressure core-degas experiments all indicated general agreement with the pre-cruise analysis regarding the location and approximate concentration of gas hydrates in the sediments. We find that seismic predictions are generally consistent with log-based estimates after upscaling to seismic frequencies. We recalibrated the pre-drill model based on the new field data so that a refined version of the model could be used for future work.

The Plio-Pleistocene stratigraphic record of the Peri-Adriatic basin (eastern central Italy) is well exposed along the uplifted western margin of the basin and consists of a series of coarse-grained slope canyon fills encased in a thick succession of hemipelagic mudstones. This study deals with the detailed sedimentology, stratal architecture, and sequence-stratigraphic interpretation of two of these submarine canyon-fills (namely CMC1 and CMC2) exposed at Colle Montarone. These strata contain widespread evidence of gravity-driven sedimentation processes, with high-and low-density turbidity currents, slumps and cohesive debris flows being responsible for most of the sediment transport and deposition. Beds are organised into four recurrent lithofacies, each corresponding to a specific deep-water depositional element: (i) clast-supported conglomerates (channel complexes); (ii) thin-bedded sandstones and mudstones (levee-overbank); (iii) very thinly-bedded mudstones (tributary channels); (iv) pebbly mudstones and chaotically bedded mudstones (mass-transport complexes). One of the most conspicuous attributes of the canyon-fill sediments exposed at Colle Montarone is their pronounced cyclic packaging, resulting from several pulses of erosion and fill. The lithofacies listed above combine to form a number of discontinuity-bound stratal packages, or high-frequency depositional sequences, each characteristically having an overall fining-upward character. Within sequences, systematic vertical trends in their constituent lithofacies define two main stratigraphic motifs, namely Motif-1 and Motif-2, which are typical of CMC1 and CMC2, respectively. Each sequence is deemed to reflect cyclical changes in volume, composition, and rheology of sediment gravity flows entering the canyons and comprises a basal unconformity (sequence boundary), succeeded by a high net-gross channel-levee complex (lowstand systems tract), overlain by a succession of either a low net-gross heterolithic deposits (early transgressive systems tract, Motif-1 sequences) or mass-transport deposits (transgressive to falling stage systems tract, Motif-2 sequences). Given the severe Icehouse climatic regime during the Pleistocene, the cyclic arrangement is most reasonably attributed primarily to repeated glacio-eustatic fluctuations in global sea level, which regulated the flux of terrigenous clastic sediment to the slope and basin-floor settings. Results from this paper are directly applicable to the oil and gas industry when making predictions of reservoir and seal relationships within slope turbidite systems developed during periods of high-frequency, eustatic sea-level fluctuations.

Samples collected in the deep Nazaré Canyon and at the adjacent slope, during the HERMES RRS Discovery D297 cruise (2005), were analysed for metazoan meiofauna, nematode structure and diversity and its relation to quality and quantity of sedimentary organic material. The amount and quality of organic matter available for direct consumption was much higher in the canyon compared to the slope and positively correlated with high nematode abundances (795-1171 ind. 10 cm À2 ) and biomass (93.2-343.5 mg dry weight 10 cm À2 ), thus leading to higher standing stocks. Canyon nematode assemblages also showed particular adaptations (e.g. higher trophic complexity, variability of nematode morphology, and presence of opportunistic genera) to canyon conditions, particularly in the deeper sediment layers. The Nazaré Canyon's nematode diversity was slightly lower than that of the adjacent slope and its assemblages were characterised by a higher dominance of certain genera. Still, the canyon contributes considerably to total Western Iberian Margin diversity due to different assemblages present compared to the slope. Furthermore, the harsh conditions in terms of hydrodynamic disturbance and the high organic matter flux are likely to have a negative impact on the establishment of species rich meiobenthic communities, especially in the canyon axis.

In 2007, the upper part of a submarine canyon system located in water depths between 138 and 1165 m in the South West (SW) Approaches (North East Atlantic Ocean) was surveyed over a 2 week period. High-resolution multibeam echosounder data covering 1106 km 2 , and 44 ground-truthing video and image transects were acquired to characterise the biological assemblages of the canyons. The SW Approaches is an area of complex terrain, and intensive ground-truthing revealed the canyons to be dominated by soft sediment assemblages. A combination of multivariate analysis of seabed photographs (184-1059 m) and visual assessment of video ground-truthing identified 12 megabenthic assemblages (biotopes) at an appropriate scale to act as mapping units. Of these biotopes, 5 adhered to current definitions of habitats of conservation concern, 4 of which were classed as Vulnerable Marine Ecosystems. Some of the biotopes correspond to descriptions of communities from other megahabitat features (for example the continental shelf and seamounts), although it appears that the canyons host modified versions, possibly due to the inferred high rates of sedimentation in the canyons. Other biotopes described appear to be unique to canyon features, particularly the sea pen biotope consisting of Kophobelemnon stelliferum and cerianthids.

Canyon of Capbreton: new morphostructural and morphosedimentary approaches. First results of the ITSAS cruise. A recent cruise of the Suroît using new technologies for acquisition and processing of acoustic data (very high-resolution seismic and swath mapping) associated to an accurate satellite positioning, allowed producing a new bathymetric map of the upper part of the canyon. It shows the meandering shape of the canyon and superposed polyphase terrace. Such a morphology is due to activity of gravity flows that occurred as soon as the Upper Eocene. Very high-resolution seismic data allowed to confirm the influence of old tectonic structures on the location and the general shape of the canyon and to show that neotectonics that affects Plio-Quaternary deposits corresponds to recurrent activity of old tectonic structures.  2001 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS canyon of Capbreton / South Aquitaine margin / structural control / geomorphology / turbidity currents Résumé-Une campagne récente du N/O Le Suroît, utilisant les nouvelles techniques d'acquisition et de traitement des données acoustiques (sismique très haute résolution, sondeur multifaisceaux) a permis d'établir une carte bathymétrique très précise et détaillée de la partie supérieure du canyon, montrant un tracé méandriforme et l'étagement de terrasses polyphasées. Il est montré qu'une telle morphologie a pu se mettre en place par des processus d'écoulements gravitaires dès l'Éocène supérieur. Par ailleurs, les données de sismique très haute résolution ont permis de confirmer le rôle joué par les structures anciennes dans la localisation et le tracé général du canyon, et de montrer que la néotectonique affectant des terrains Plio-Quaternaire correspond à un rejeu de ces anciennes structures.  2001 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS canyon de Capbreton / marge Sud-Aquitaine / contrôle structural / géomorphologie / courants de turbidité Abridged version * Correspondance et tirés à part.

1. Cold-water coral (CWC) ecosystems are protected both in national and international waters. They are considered Vulnerable Marine Ecosystems and, in addition, meet the criteria to be defined ecological or biological significant areas. 2. Two new sites of the "Sardinian CWC province" were discovered by means of remotely operated vehicle surveys in two submarine canyons in the northeastern portion of the Sardinian continental margin, at depths ranging from 230 to 430 m. 3. Dense and healthy patches of small and medium-sized Madrepora oculata colonies were found dwelling on rocky walls and inclined silted soft bottoms. 4. A rich and diverse associated megafauna was found within both live and dead portions of the coral framework. In addition, the presence of benthic litter and derelict fishing gears were also documented. 5. These results further extend the "Sardinian CWC province" extension, providing insights of a potential CWC network along the Sardinian continental margin with implications for the Mediterranean mosaic of CWC provinces, further stressing the need for urgent conservation measures for these habitats.

High-resolution acoustic data indicate that sediment erosion is a significant process in the continental slope of Yeşilırmak River Fan, occurring both related to the submarine canyons and in the open continental slope. The sediment processes observed along the slope consist of sliding and debris flows on the canyon walls together with the recent erosional surfaces at the canyon heads wherever the canyons exist, and slides and related scarp features structurally controlled by rotational faults in the central part of the open continental slope.

The distribution of megabenthic epifauna (invertebrates) in the Balearic Basin (western Mediterranean) has been analyzed at depths between 427 and 2265 m after compiling samplings performed in 1985-1992 and 2007-2008 with an OTSB-14 bottom trawl. 84 epibenthic taxa of invertebrates (excluded decapod crustaceans) were collected. Epibenthic assemblages were organized in five groups (n-MDS analyses) as a function of increasing depth: upper slope assemblage, U, hauls between 427 and 660 m; middle slope assemblages M1 and M2, hauls between 663-876 m and 864-1412 m, respectively; lower slope assemblages L1 and L2, hauls between 1488-1789 m and 1798-2265 m, respectively). We found significant differences in assemblage composition between all depth-adjacent pairs of groups. Trends in the distribution of biomass vs. depth and within assemblages varied when hauls taken over insular were compared to those over mainland slopes. Over insular slopes we found (n-MDS) only four distinct depth assemblages, with significant differences between all depth-adjacent group pairs, except between L1 and L2. Over the mainland slope, two peaks of biomass situated at U (427-660 m) and at L1 (1488-1789 m) were clearly identified, attributable to the echinoid Brissopsis lyrifera and holothurian Molpadia musculus at U and to the synallactid holothurian Mesothuria intestinalis at L1. The distribution of biomass vs. depth on insular slopes did not follow this pattern, showing no significant biomass peak below 1000 m and a total biomass an order of magnitude lower than adjacent to the mainland. After compiling available environmental data over the mainland slope off Barcelona, we found coincidence between the peak biomass of Mesothuria intestinalis and: i) a significant increase of labile OM (%OrgC, C/N, hydrolizable aminoacids-EHAA, and the EHAA/THAA-total hydrolizable aminoacids-ratio) over 1600 m; and ii) an increase of turbidity and T at 1500-1600 m in February 2008. We suggest that such OM inputs must likely be associated to the formation of nepheloid layers close to submarine canyons, probably associated with oceanographic processes in deep water masses in the area. This would explain why aggregations of M. intestinalis were linked to the mainland part of the Balearic basin, with highest densities located south of canyons. If hotspots of biomass as cited here for M. intestinalis are regulated by factors such as river inputs, both natural climatic changes (e.g. changes in rainfall regimes) and human impact (e.g. river damming) may affect deep-Mediterranean communities below 1000 m.

This study describes the foraminifera and facies of a large submarine canyon: the Bass Canyon, in the Gippsland Basin off the coast of southeastern Australia. The study incorporates facies
analyses and interpretations of three types of foraminiferal distributional data: forms alive at time of collection, recently dead forms and relict forms. Four principle biofacies types occur: (1) middle shelf to shelf-break carbonate sand; (2) oxic upper to middle bathyal carbonate sand and gravel, with abundant
bryozoans; (3) reduced oxic middle bathyal carbonate sand and gravel and (4) lower bathyal oxic muddy sand to Globigerina Ooze.
Correspondence Analysis of the 61 parameters (percentage abundance of foraminifera and % carbonate) in 36 samples yielded a clear depth-related pattern, although other related parameters such as dissolved oxygen and substrate also exert control on the foraminiferal assemblages. Relict foraminifera are restricted to shelfal depths, shallower than 145 m. This pattern is similar to other shelf regions in Australia, where shelf areas were exposed during the Last Glacial Maximum, reworking shelf facies shallower than 150 m. The distribution of living foraminifera is similar to the distribution of the total assemblage, suggesting that the region has not been significantly mixed by wave,
slump or bioturbation processes.
The majority of the modern Bass Canyon foraminiferal assemblages are cosmopolitan species, with few (semi-)endemic taxa that are mostly restricted to the shelf. These modern deeper-living forms are more conservative since they evolved in relatively lower stress eutrophic environments than their shallower oligotrophic dwelling contemporaries.
The foraminiferal and facies analogues of this study on the Bass Canyon may be used as a modern palaeoenvironmental analyses of the Gippsland and Otway Neogene sedimentary deep-sea successions. This will lead ultimately to a better understanding of the evolution of the basins in southeastern Australia, in an area influenced by the Southern Ocean during the Cenozoic

The macrofaunal assemblages from three Portuguese submarine canyons, Nazaré, Cascais and Setúbal were studied from samples collected at their upper (900–1000 m), middle (3200–3500 m) and lower sections (4200–4500 m) and at the adjacent open slopes (∼1000 m), during the HERMES cruises D297 (R.R.S. Discovery, 2005) CD179 (R.R.S. Charles Darwin, 2006) and 64PE252 (R.V. Pelagia, 2006). The taxonomic composition and patterns in biodiversity, abundance and community structure of the benthic macrofauna were described. Annelida (42.1% of total abundance; 137 species) and Arthropoda (20.6%; 162 species) were, respectively, the most abundant and the most species-rich Phyla among the 342 taxa identified during this study. Multivariate analyses showed significant differences between and within canyons and between canyons and open slope assemblages. At their upper section, canyons supported higher macrofauna abundance but slightly lower biodiversity than the adjacent slopes at similar depth. In all canyons abundance reached the highest value in the middle section and the lowest in the upper section, with marked fluctuations in Nazaré (474–4599 ind. m−2) and lower variability in Cascais (583–1125 ind. m−2). The high abundance and dominance of the assemblages in the middle section of Nazaré and Setúbal was accompanied by depressed biodiversity, while in Cascais, Hurlbert's expected species richness showed increasing values from the upper to the middle canyon, and maintained the high values at the lower section. Overall, the Nazaré Canyon showed the lowest expected species richness (ES(100): 16–39) and the Cascais Canyon the highest (39–54). There was a significant negative Kendall's correlation between total organic carbon concentrations in the superficial sediments and ES(100) and a significant positive correlation between total nitrogen and macrofauna density. The influences of organic enrichment, sediment heterogeneity and hydrodynamic regime on the abundance, diversity and community structure of the macrofauna are discussed. It is suggested that altered and localised environmental conditions in the Portuguese canyons play an important role in modifying more common abundance and diversity bathymetric patterns evident in many continental slope environments.

Quantifying the characteristics of the turbidity currents that are responsible for the erosion, lateral migration and filling of submarine channels maybe useful for predicting the distribution of lithofacies in channel fill and levee reservoirs. This paper uses data from a wellstudied submarine channel in Amazon Fan in an attempt to reconstruct the velocity, thickness, concentration, duration, recurrence rates and vertical structure of turbidity currents in this long sinuous channel. Estimates of flow conditions are derived from the morphology of the channels and the characteristics of the deposits within them. In particular, the availability of information on the sediment distribution with respect to the channel topography at the time of deposition allows for insights into the vertical structure of the flow, a key property that has been so far poorly understood. Integration of flow constraints from well and seismic data or from detailed analysis of outcrop with numerical flow models is a critical step toward a complete understanding of the flow and associated deposits. Turbidity currents in sinuous submarine channels, exemplified by Amazon Channel, are found to last for tens of hours and occur on a regular, quasi-annual basis. Model results suggest that these flows had, on average, velocities ranging from 2 to 4 m/s in the canyon/upper fan which decreased to 0.5-1 m/s in the lower fan, travelling in excess of 800 km. The model turbidity currents were subcritical over most of the channel length, indicating a low degree of water entrainment and low rate of deceleration down the channel. The formation of such long, sinuous channels is intrinsically associated with frequent, long-duration, subcritical turbidity currents carrying a silt-dominated sediment load. q

The particles collected in a sediment trap in the Gaoping Submarine Canyon provided a high resolution PAH profile that traces typhoon (Kalmaegi) induced particle movement. Results provide further evidence that submarine canyons are an effective conduit for transporting terrestrial contaminants such as PAHs, particularly as typhoonrelated hyperpycnal plumes at river mouths and ensuing turbidity currents in the submarine canyon. Observations here show that two typhoon-triggered turbidity currents passed the sediment trap. The beginnings of the two turbidity currents showed strong pyrogenic signatures suggesting coal and biomass burning sources. These turbidity currents carried enormous amounts of particulate PAHs (510 kg in 12.5 h), which accounted for 4.2% of the annual PAH flux from the Gaoping River. The PAH signature allowed the typhoon effect to be broken into five stages: (I) period before the typhoon effect (marine sources), (II) typhoon induced currents (resuspended sediments), (III) down-canyon flow (pyrogenic particles from northwestern shelf), (IV) river plume impact with two turbidity currents (arrival of terrestrial particles), and (V) end of typhoon discharge of anthropogenic PAHs to the canyon head.

The main break-in-slope on the northern submarine flank of Molokai at 31500 to 31250 m is a shoreline feature that has been only modestly modified by the Wailau landslide. Submarine canyons above the break-in-slope, including one meandering stream, were subaerially carved. Where such canyons cross the break-in-slope, plunge pools may form by erosion from bedload sediment carried down the canyons. West Molokai Volcano continued infrequent volcanic activity that formed a series of small coastal sea cliffs, now submerged, as the island subsided. Lavas exposed at the break-in-slope are subaerially erupted and emplaced tholeiitic shield lavas. Submarine rejuvenated-stage volcanic cones formed after the landslide took place and following at least 400^500 m of subsidence after the main break-in-slope had formed. The sea cliff on east Molokai is not the headwall of the landslide, nor did it form entirely by erosion. It may mark the location of a listric fault similar to the Hilina faults on present-day Kilauea Volcano. The Wailau landslide occurred about 1.5 Ma and the Kalaupapa Peninsula most likely formed 330 þ 5 ka. Molokai is presently stable relative to sea level and has subsided no more than 30 m in the last 330 ka. At their peak, West and East Molokai stood 1.6 and 3 km above sea level. High rainfall causes high surface runoff and formation of canyons, and increases groundwater pressure that during dike intrusions may lead to flank failure. Active shield or postshield volcanism (with dikes injected along rift zones) and high rainfall appear to be two components needed to trigger the deep-seated giant Hawaiian landslides. ß

The application of high‐resolution seismic geomorphology, integrated with lithological data from the continental margin offshore The Gambia, northwest Africa, documents a complex tectono‐stratigraphic history and seascape evolution through the Cretaceous. This reveals the spatial‐temporal evolution of submarine canyons by quantifying the related basin depositional elements and providing an estimate of intra‐ vs extra‐basinal sediment budget. The margin developed from the Jurassic to Aptian as a carbonate escarpment. Subsequently, an Albian‐aged wave‐dominated delta system prograded to the paleo‐shelf edge. This is the first major delivery of siliciclastic sediment into the basin during the evolution of the continental margin, with increased sediment input linked to exhumation events of the hinterland. Subaqueous channel systems (up to 320 m wide) meandered through the pro‐delta region reaching the paleo‐shelf edge, where it is postulated they initiated early submarine canyonisation of the margin. The canyonisation was long‐lived (ca. 28 Myr) dissecting the inherited seascape topography. Thirteen submarine canyons can be mapped, associated with a Late Cretaceous‐aged regional composite unconformity (RCU), classified as shelf‐incised or slope‐confined. Major knickpoints within the canyons and the sharp inflection point along the margin are controlled by the lithological contrast between carbonate and siliciclastic subcrop lithologies. Analysis of the base‐of‐slope deposits at the terminus of the canyons identifies two end‐member lobe styles, debris‐rich and debris‐poor, reflecting the amount of carbonate detritus eroded and redeposited from the escarpment margin (blocks up to ca. 1 km3). The vast majority of canyon‐derived sediment (97%) in the base‐of‐slope is interpreted as locally derived intra‐basinal material. The average volume of sediment bypassed through shelf‐incised canyons is an order of magnitude higher than the slope‐confined systems. These results document a complex mixed margin evolution, with seascape evolution, sedimentation style and volume controlled by shelf‐margin collapse, far‐field tectonic activity and the effects of hinterland rejuvenation of the siliciclastic source.

On the Gulf of Lions margin, the Messinian Salinity Crisis (MSC) event led to a significant and widespread erosion of the Miocene shelf and slope. It is thus difficult nowadays to restore the morphology of the margin at the beginning of the crisis, and to study the Middle-Upper Miocene series rarely preserved from erosion. In this study, thanks to the use of multichannel seismic reflection data from the Gulf of Lions western slope, it has been possible to image the Miocene slope deposits. Interpretation of the data reveals several diachronic sediment bodies just beneath the Miocene/Pliocene boundary. These bodies are related to slope erosional-depositional complexes, underlain by erosional unconformities outlined by seismic reflector truncations. They are V-or Ushaped in cross section. Over their mapped extent, these bodies are typically 8-12 km wide and incise up to 600 ms TWTT into the Miocene slope deposits. In plan view, they are roughly elongated NW-SE, perpendicularly to the present day shelf break, and they progressively migrate towards the South-East. We interpret these seismic bodies as buried Miocene submarine canyons pre-dating the dramatic drawdown related to the MSC. In this study we try to constrain their age, and we discuss the events that may be at their origin. We also discuss the long-term impact of these slope canyons on the evolution of the margin.

Previous projects in the Gulf of Lion have investigated the path of terrigenous material in the Rhone deltaic system, the continental shelf and the nearby canyon heads. This study focuses on the slope region of the Gulf of Lion to further describe particulate exchanges with ocean's interior through submarine canyons and atmospheric inputs. Nine sediment traps were deployed from the heads to the mouths of Lacaze-Duthiers and Cap de Creus submarine canyons and on the southern open slope from October 2005 to October 2006. Sediment trap samples were analyzed by CuO oxidation to investigate spatial and temporal variability in the yields and compositional characteristics of terrigenous biomarkers such as ligninderived phenols and cutin acids. Sediment trap data show that the Dense Shelf Water Cascading event that took place in the months of winter 2006 (January, February and March) had a profound impact on particle fluxes in both canyons. This event was responsible for the majority of lignin phenol (55.4%) and cutin acid (42.8%) inputs to submarine canyons, with lignin compositions similar to those measured along the mid-and outer-continental shelf, which is consistent with the resuspension and lateral transfer of unconsolidated shelf sediment to the canyons. The highest lithogenic-normalized lignin derived phenols contents in sediment trap samples were found during late spring and summer at all stations (i.e., 193.46 lg VP g À1 lithogenic at deep slope station), when river flow, wave energy and total particle fluxes were relatively low. During this period, lignin compositions were characterized by elevated cinnamyl to vanillyl phenol ratios (>3) at almost all stations, high p-coumaric to ferulic acid ratios (>3) and high yields of cutin acids relative to vanillyl phenols (>1), all trends that are consistent with high pollen inputs. Our results suggest marked differences in the sources and transport processes responsible for terrigenous material export along submarine canyons, mainly consisting of fluvial and shelf sediments during winter and atmospheric dust inputs during spring and summer.

Submarine canyons can efficiently drain sediments from continental margins just as river systems do in subaerial catchments. Like in river systems, submarine canyons are often arranged as complex drainage networks that evolve from patterns of erosion and deposition. In the present paper we use a morphometric analysis of submarine canyon-channel long-profiles to study the recent sedimentary history of the Valencia Trough turbidite system (VTTS) in the NW Mediterranean Sea. The VTTS is unique in that it drains sediment from margins with contrasting morphologies through a single "trunk" conduit, the Valencia Channel. The Valencia Channel has been active since the late Miocene, evolving in response to Plio-Quaternary episodes of erosion and deposition. The integrated analysis of long-profiles obtained from high-resolution bathymetric data across the entire turbidite system shows evidence for transient canyon incision in the form of knickpoints and hanging tributaries. Multiple factors appear to have triggered these periods of incision. These include a large debris flow at 11,500 yr BP that disrupted the upper reaches of the VTTS and glacio-eustatic lowstands that forced shifting of sediment input to the VTTS. Based on these inferences, long-term time-averaged incision rates for the Valencia Channel have been estimated. The evidence we present strongly suggests that Foix Canyon has played a key role in the drainage dynamics of the VTTS in the past. This study builds conceptually on a recent modeling study that provides a morphodynamic explanation for the long-term evolution of submarine canyon thalweg profiles. The procedure and results from this work are of potential application to other submarine sediment drainage systems, past and present, including those containing mid-ocean type valleys like the Valencia Channel.

Samples collected at two different depths (ca. 3200 and ca. 4200 m) in the Setú bal and Cascais canyons off the Portuguese coast, during the HERMES RRS Charles Darwin cruise CD179, were analysed for (1) sediment biogeochemistry (TOC, TN) and (2) composition, and structural and trophic diversity of nematode communities. Multivariate PERMANOVA analysis on the nematode community data revealed differences between sediment layers that were greater than differences between canyons, water depths, and stations. This suggests that biogeochemical gradients along the vertical sediment profile are crucial in determining nematode community structure. The interaction between canyon conditions and the nematode community is illustrated by biogeochemical patterns in the sediment and the prevalence of nematode genera that are able to persist in disturbed sediments. Trophic analysis of the nematode community indicated that non-selective deposit feeders are dominant, presumably because of their non-selective feeding behaviour compared to other feeding types, which gives them a competitive advantage in exploiting lower-quality food resources. This study presents a preliminary conceptual scheme for interactions between canyon conditions and the resident fauna.

Samples collected at two different depths (ca. 3200 and ca. 4200 m) in the Setú bal and Cascais canyons off the Portuguese coast, during the HERMES RRS Charles Darwin cruise CD179, were analysed for (1) sediment biogeochemistry (TOC, TN) and (2) composition, and structural and trophic diversity of nematode communities. Multivariate PERMANOVA analysis on the nematode community data revealed differences between sediment layers that were greater than differences between canyons, water depths, and stations. This suggests that biogeochemical gradients along the vertical sediment profile are crucial in determining nematode community structure. The interaction between canyon conditions and the nematode community is illustrated by biogeochemical patterns in the sediment and the prevalence of nematode genera that are able to persist in disturbed sediments. Trophic analysis of the nematode community indicated that non-selective deposit feeders are dominant, presumably because of their non-selective feeding behaviour compared to other feeding types, which gives them a competitive advantage in exploiting lower-quality food resources. This study presents a preliminary conceptual scheme for interactions between canyon conditions and the resident fauna.