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We study an area little known of the Atlantic Patagonian margin from 44°30′S to 47°40′S and from 59°W to nearly 61°W. The multi-beam bathymetry coupled with high resolution seismic reflection profiles, has provided details on the morphology and shallow acoustic structure on this area. The main morphological characteristics of the seafloor features on the shelf and middle slope are described. The Atlantic Patagonian continental shelf north of 45°40′S is located at a depth of 170–200 m, south of this latitude the shelf edge is at 128 to 200 m. The shelf surface is marred by circular depression and ridges oriented oblique to the shelf edge. The upper slope and upper middle slope are plowing by icebergs from Antarctica in Pleistocene and local reefs of cold-water coral further enhance the topography of the area. In the middle slope there are two terraces, the 20 to 60 km wide Nagera and the 15 to 60 km wide Perito Moreno terraces, showing moats, hollows, pot holes, sediment drifts and sediment waves. The terraces may have been formed in Late Miocene whereas the other forms are of Pleistocene age. Other features are a sediment swell south of 47°S and seven submarine canyons on the middle slope. These incipient canyons have been developed in the middle slope by retrogressive erosion, some terminating on the upper middle slope, and others on the upper slope and the Canyon 6 breaching the shelf edge. Individual seafloor features existing on the Atlantic Patagonian Margin have been classified into two main groups according to their origin: along and across-slope processes. These primary agents were supplemented by endogenic processes such as expulsion of gas/water, diapirism of high-pressure mud and folding/faulting. The results suggest that today down-slope processes on the slope are practically non-existent and that the morphology of the upper and middle slope is slowly being remolded by along-slope bottom currents.

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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 44°30'S and 48°S 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. These include incisions from just a dozen of metres to 650 m, straight to highly meandering sections with sharp bends, well-developed levees and walls that reach 35° in slope gradient, hanging branches, conspicuous axial incisions and multiple knickpoints. Only the northernmost canyon indents in the continental shelf, whereas the others start at the limit between the upper and middle slopes, and are often fed by small, straight, leveed gullies. The action of both across-slope processes represented by submarine canyons and along-slope processes represented by terracing and scouring conform the ACM as a peculiar mixed margin, with the presence of both contour and gravity currents at the same place at the same time. We propose that at present, along-slope erosion and transport mainly occurs along the Perito Moreno terrace, whereas across-slope processes are much more dominant in the Nagera terrace. Erosive bedforms such as crescent scours, generated by contour currents, contribute to the progressive bottom-up erosion of the Nagera terrace and act as an initial collector of across-slope transported sediment, that later, due to flow focusing and recurrence, incise and interconnect creating definitive canyons that progress upslope by retrogressive erosion until their head indents the shelf break. Changes in the balance between across-slope and along-slope transport would imply a disequilibrium in the combination of processes leading to canyon formation, producing canyon abandonment, and partial or total filling. These changes could be produced by a variation in the depth of the main interfaces of Antarctic water masses leading to either an increase or a decrease in the erosion and transport capacity of contour currents, and/or by an enhancement of across-slope transport related to an increase of sediment availability., Sí

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Widespread volcanism off eastern Spain in the western Mediterranean is associated with Cenozoic crustal attenuation and sinistral motion along the Trans-Moroccan–Western Mediterranean–European mega shear, extending from northern Morocco to the North Sea via the Alboran Basin, eastern Iberia, the Valencian and Lyons basins, France and Germany. The Quaternary Columbretes Islands volcanic field is the most prominent example of this volcanism associated with this mega shear. The islands are located in the Ebro continental shelf on top of a structural horst probably made of Paleozoic metamorphic rocks. Surrounding the emerged islands are volcanic structures and associated flows partially mantled by a sediment drift whose morphology is controlled by the southwestward flowing Catalan Current. This association is rather unique and appears to have never been described from a continental shelf in the Mediterranean Sea or outside the sea. The morphology of both kinds of structures, obtained by means of swath bathymetry data and very-high resolution seismic profiles, is presented in this study. They provide striking images of this previously unstudied part of the western Mediterranean seafloor. These images suggest that the volcanic structures are intruded into the surficial Holocene sediments indicating that volcanism in the Columbretes has extended into Holocene., Sí

In this paper we discuss the results of a swath bathymetric investigation of the Canary archipelago offshore area. These new data indicate that volcanism is pervasive throughout the seafloor in the region, much more that would be suggested by the islands. We have mapped tens of volcanic edifices between Fuerteventura and Gran Canaria and offshore Tenerife, La Gomera, El Hierro and La Palma. Volcanic flows are present between Tenerife and La Gomera and salic necks dominate the eastern insular slope of La Gomera. This bathymetry also supports land geologic studies that indicate that the oceanic archipelago has acquired its present morphology in part by mass wasting, a consequence of the collapse of the volcanic edifices. In the younger islands, Tenerife, La Palma and El Hierro, the Quaternary (1.2 to 0.15 Ma) debris avalanches are readily recognizable and can be traced offshore for distances measured in tens of km. Off the older islands, Lanzarote, Fuerteventura, Gran Canaria and La Gomera (

Book cover Geophysics of the Canary Islands pp 59–90Cite as Comparison of volcanic rifts on La Palma and El Hierro, Canary Islands and the Island of Hawaii Download book PDF Comparison of volcanic rifts on La Palma and El Hierro, Canary Islands and the Island of Hawaii J. Acosta, E. Uchupi, D. Smith, A. Muñoz, P. Herranz, C. Palomo, P. Llanes, M. Ballesteros & ZEE Working Group Chapter 649 Accesses 4 Citations Abstract The meso-scale (km) morphology of the well-studied volcanic rift zones on the Island of Hawaii is compared to the morphology of the lesser known rift zones of La Palma and El Hierro, Canary Islands. We find that there are both differences and similarities in their morphologic characteristics. In general, the rift zones on La Palma and El Hierro are shorter (a few tens of km in length) than those on Hawaii (ranging up to >100 km in length), perhaps reflecting both magma supply and composition. Many of the rift zones on Hawaii have well defined axial zones, both on-and offshore. In contrast, the rift zones on La Palma and El Hierro display various geometries ranging from linear ridges having smooth to irregular crests to structures with a broad fan-like morphology in plan view. The pronounced fanning may be a reflection of: 1) the stress field within the rift being insufficient to trap dikes within a narrow region, 2) dike injection and volcanism shifting laterally through time, 3) volcanoes building nearly one atop of another in the Canary Islands, superimposing the stress field of one structure on the other and thus yielding a more complex distribution of gravitational stresses, and 4) low rate of magma supply producing low magma pressures and thus randomly oriented dike injections. Irregularities and curvature along the axes of the rifts on La Palma and El Hierro may be a reflection of differences in the rate of magma production. Unlike the volcanoes on the Island of Hawaii there may be insufficient volumes of lavas erupted on La Palma and El Hierro to smooth out irregularities. The superposition of rifts from different volcanoes may also add to topographic irregularities in the Canary Islands, especially if eruption rates are low. 1

Circular to elliptical mounds in the Canary Channel with reliefs of 75 to 375 m and diameters of 4 to 8 km partially surrounded by moats with reliefs of 25 to 75 m, were formed by piercement of the seafloor by Mesozoic evaporites. Several long gullies, Sí

As part of the ‘National Hydrographic and Oceanographic Research Plan for the Spanish Exclusive Economic Zone’, multibeam bathymetry and seismic reflection profiles were obtained in the Canary Islands aboard the R/V Hespérides. The submarine flanks of the Anaga offshore extension of Tenerife Island are here studied to analyze its geomorphology. In the north sector of the Anaga submarine massif, the extension of the Anaga Debris Avalanche has been mapped for the first time, and a volume of 36 km3 was calculated. The relationship between the Anaga and Orotava Debris Avalanches is also described. Faulting has been recognized as a key process for the occurrence of debris avalanches and the growth of volcanic lineaments. Moreover, faulting affects previous structures and the channelling of debris flows. Structural analysis shows the typical radial pattern of an oceanic island. In addition, a NE-SW dominant direction of faulting was obtained, consistent with the Tenerife Island structural trend seen in the Anaga Massif and Cordillera Dorsal. NW-SE and E-W are two other main trends seen in the area. Special interest is manifest in two long faults: ‘Santa Cruz Fault’ bounds the southern edge of Anaga offshore Massif with a length of 50 km and a direction that changes from NE-SW to almost E-W. The Güimar Debris Avalanche was probably channeled by this fault. The ‘Guayotá Fault’ was recognized in several seismic profiles with a N-S direction that changes towards NW-SE at its southern end. This fault affects the more recent sediments with a vertical offset of 25–30 m, along 60 km. It has been interpreted as a transpressive strike-slip fault. 1

Tectonic elements of the Puerto Rico northern peninsular slope are the creations of Mesozoic-Paleogene southerly directed subduction which formed an island arc-forearc basin-accretionarywedge complex, Oligocene-Pliocene carbonate platform construction during a tectonically stable phase, a northerly collapse of the carbonate platform and subsidence of the Puerto RicoTrench in the Pliocene and the initiation of the present oblique subduction regime in theQuaternary. Collapse of the platform and trench may be due to extension of the Greater AntillesRidge caused by counterclockwise rotation of Puerto Rico-Virgin Islands platelet resulting froma change in plate geometry in the Miocene-Pliocene. 0

In this paper we presente evidence from submarine slides locate south of Mallorca Island. This study is based on the bathymetric map obtained by the multi beam echosounders SIM RAD EM I000 and EM I2, together with the analysis of several seismic reflection profiles of high resolution logging with the SPARKER system mod. 267. Each method generated a specific data set. Both bathymetric and seismic data set are complementary one to another. Two main fault lineations have been identified; NE-SW (Betic) and NW-SE. A clear sequence of turbiditic sediments is perfectly recognize in the area, flanked by recent faulting., Sí

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The ZEE99 oceanographic cruise was carrided out aboard B.I.O. Hespérides by the Instituto Español de Oceanografía and the Instituto Hidrográfico de la Marina, and was located in Canary Islands. In order to study the bathymetry o f the Gran Canaria northeast ocean floor; a Simrad EMI 2 multi beam echosounder was used. These data allow us to produce a detailed bathymetric map and make it possible to infer the caracteristics and geologic processes that led to a major development in the investigation o f submarine geomorphology around the Canary Islands. 0

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In this paper w e present th e general objetives and scope o f the Spanish Exclusive Econom ic Zone program and the preliminary results of the first cruise carried out by Hydrographic Institute of the Navy (IHM) and the Spanish Oceanographic Institute (IEO) in the continental margin off Valencia - Balearic Islands. The 2 2 0 geophysic al p ro file s to ta liz e s 9 2 0 4 km . o f g ra vim e try, magnetic s , sin gle beam echosounder, sub-bottom profiler and multibeam echosounder, covering 12.000 Km2. Morphologically, the first processed area, the Valencia slope, shows a striking pattern of channels with low sinuosity index and deeply incised in the slope that flow in NW-SE direction to the Valencia Deep.This area also shows a general cover of unconsolidated sediments in different slumped degrees

The oceanographic cruise Teide-95 was carried out by the Instituto Español de Oceanografía. The main objetive was the analysis of the ocean floor around Tenerife island. In order to determinate the bathymetry of this area, a Simrad EM-12 multibeam echosounder was used. These data allow us to produce a detailed bathymetric map. Two well differentiated areas have been established. One is in the north slope of the island, characterized by incised valleys, fan morphologies and megablock fields. The second area is the south slope, which consists of two provinces, characterized by differences in the dimensions of the insular platform and the sedimentary thickness, Sí

The applications of multibeam systems with their high resolutions and capability to eliminate "blind zones" between track lines, characteristic of single beam systems, had led to a major development in the investigation of submarine geomorphology. In this study we compare the results obtained with single and m u ltib e a m echosounders survey o f a sea m ou nt east o f Ibiza, Balearic islands. As illu s tra te d by these date sets the multibeam system is better able than the single-beam system to define the configuration of this high. Multibeam systems also led themshelves to the creation of computer generated physiographic diagrams displaying the information provided by the Simrad multibeam system available on the R/V Hesperides, and makes it possible for the investigator to infer the geologic processes that have molded the seamount, Sí

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Dans la presente communication nous faisons une étude de la flotte chalutière de la Galice (ports de La Coruña et Vigo) qui travaille aux régions VII b, c, j, k. Nous fournissons des données sur las captures et les captures par unité d'effort en 1974 pour les espèces les plus importantes économiquement pour les différents groupes de bateaux dans lesquels nous avons divisé la flotte. Les variations saisonnières de ces espèces sont étudiées aussi que la distribution des tailles du merlu (Merluccius merluccius L.) pendant cette année là.

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This document describes results of computing correlations between different CPUE series of hake (Northern Stock). Results show that significant correlations between some series appeared when same lag was allowed between series. Lesconil artisans CPUE (fishing in division VIlla) in year t seems to be correlated to CPUE La Rochelle "artlsans" on the same year, to La Coruña trawlers fishing in subarea VII on year (t+1) and to La Rochelle "hauturiers" fishing in subarea VII on year (t+3) ; these "hauturiers" CPUE is correlated with Lorient trawlers CPUE fishing in divisions IVa + VIa two years later. These correlations allow to become more confident on these CPUE series. However, it is difficult to believe that plots like the one in fig. 7 can prove that there is a direct cause to affect relationship between hake CPUE from "artisans" in subareas VII and VIII and hake CPUE from "hauturiers" fishing in divisions IVa + VIa two years later.

Changes in the catch level of hake since 1936 to 1977 corresponding to subareas IV, VI, VII and VIII -area of distribution of the northern stock of hake, plus division VIIIc- are described and analysed. Four periods can be defined in relation to the catch level: 1) The wars period, 1936-1944, with catches reduced for the course of the spanish civil war, and the second big war; 2) Post-war period, 1945-47, when the effort recovered suddenly at least the prewar level, with very high catches consisting of a portion of the big standing stock accummulated during the wars period plus the surplus.; 3) 1953-1964, with catches stabilized at a level between 70 and 85000 tons; and 4) 1964-77, with catches between 60 and 70000 tons. The document shows how most of the reduction of the catch happened in divisions lVa+Vla, and atributes this decrease in the catch of hake to the strong increaee in trawl effort on the Northern divisions.

In this paper, the authors try to check if there exists a relationship between catchability and stock size in the juvenile albacore surface fishery in the North Atlantic stock. The conclusions are that this relationship does not seem to take place; fishing effort reflects very well F, and CPUE changes reflect abundance changes in the stock in the period analyzed. The authors call readers' attention to the possibility that a "significant" correlation between q and N does not mean a cause to effect relationship between these two variables., Les auteurs du présent document ont tent de vérifier s'il existe une relation entre la capturabilité et la taille du stock dans la pêcherie de surface de germon juvénile du stock de l'Atlantique nord. Les conclusions sont que cette relation ne semble pas se présenter; l'effort de pêche reflète tres bien F et les changements de la CPUE illustrent ceux de l'abondance du stock pour la période analysée. Les auteurs attirent l'attention du lecteur sur la possibilité de ce qu'une corrélation "significative" entre q et N puisse ne pas signifier qu'il existe une relation de cause à effet entre ces deux variables., Este documento intenta comprobar si existe una relación entre la capturabilidad y el tamaño del stock de atún blanco juvenil en la pesquería de superficie del Atlántico Norte. La conclusión es que no existe tal relación; el esfuerzo pesquero refleja bien la F y los cambios en la CPUE reflejan cambios en la abundancia del stock durante el periodo analizado. Los autores señalan que existe una posibilidad de que una correlación "significativa" entre q y N no supone una relación causa-efecto entre estas dos variables.

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Durante la campaña «Merluza NW 74", realizada en aguas gallegas, se extrajeron los otolitos de 272 merluzas, que hicieron posible conseguir una primera aproximación a la clave talla-edad, y al relacionarlos con las capturas de merluza obtenidas durante la campaña, una estimación de la mortalidad total. Los resultados muestran que el parámetro K de la ecuación de V. Bertalanffy estaría comprendido entre 0,069 y 0,O83, Y L∞ entre 143 y 124 cm. La mortalidad de las clases 1+ a II+ sería 0,94, y de la clase III+ en adelante, de 0,6. La alta cifra de mortalidad entre las clases II+ y JII+, y el sesgo a la izquierda de la talla media de la clase II+, demostrarían una emigración hacia fuera de la costa de la merluza mayor de esta clase de edad y de clases posteriores. During "Merluza NW 74" survey, undertaken off Galicia shores in August 1974, otoliths of 272 hakes were collected, that made possible to obtain a first approach to the length-age key ; and, relating these data with hake catches during the survey, a first estímate of total mortality was obtained. Results show that the K value from V. Bertalanffy equation would be between 0,069 and 0,083, and L∞ between 143 and 124 cm. Total rnortality between age classes I+ and II+ would be 0,94, and for classes III+ and older, 0,6. The high mortality figure between I+ and III+ classes, and the skewness to the left in the mean length of this class, woulcl show an emigration offshore for the bigger hake of this age-class and older. 0