Northwest Coast Of Africa Research Articles

Late Cenozoic deep-sea benthic Foraminifera off the coast of northwest Africa (DSDP Site 369)

Upper Eocene through Pleistocene benthic foraminifers were studied in 33 samples from DSDP Site 369, off northwest Africa. A total of 197 taxa were identified. The unilocular, calcareous species were not included. The assemblage found is qualitatively the richest as compared with the faunas of the same age at other sites previously studied. One probable explanation is the relatively high productivity of this area. A faunal turnover occurred between Eocene and Oligocene time. The following Eocene species do not cross the Eocene-Oligocene boundary: Nuttallides truempyi, Bolivina cf. hebes, Bolivina beyrichi, Orthomorphina mutata and Aragonia aragonensis. the Oligocene and Pleistocene assemblages consist essentially of the same species. Based on the study of ten reliable DSDP sites studied previously and DSDP Site 369, the following 12 species are considered suitable as guide-fossils in the Oligocene-Pleistocene sequence: Buliminella carteri, Bulimina jarvisi, Turrillina alsatica, Bulimina macilenta, Cassidulina subglobosa horizontalis, Cassidulina cuneata, Cibicides notocenicus, Planulina marilana gigas, Pleurostomella obtusa, Vulvulina pennatula, s.l., Cibicides wuellerstorfi and Pyrgo murrhina. However, they are only useful for identifying major stratigraphic units (systems and subsystems). The dominant species at Site 369 are established and compared with those of other sites. The interoceanic dominant taxa typical of the bathyal Oligocene-Pleistocene sequence are determined.

Micropaleontological bathymetry of the cretaceous of western Morocco

Micropaleontologic and sedimentologic studies have been carried out on the onshore Cretaceous sediments of the Agadir and Essaouira coastal basins, and offshore deep-sea Cretaceous sediments recovered from DSDP sites 135, 137, 140, 367 and 370 off the coast of northwest Africa. Facies analysis reveals several episodes of transgression and regression in the coastal basins, suggesting a local subsidence and interplay between the rates of sedimentation and sea-level change. The Late Cretaceous transgression commenced during the Late Aptian-Albian and reached a maximum during the Early Turonian. The Late Cretaceous transgression had two major events of coastal upwelling of cold water masses during the Turonian and Maastrichtian with the production of cherts, radiolarians, non-keeled planktonic foraminifers and phosphates (Antarctic current). The Coniacian to Early Santonian was regressive, whereas the Campanian facies (keeled planktonic foraminifers) recorded a warm cycle of the Cretaceous transgression. The study has also revealed several specialized assemblages of foraminifers associated with sediment facies of particular ecologic and environmental significance. Onshore and offshore correlations reveal the evolution of the passive margin, which includes a subsidence, deep-sea circulation, variation of the calcite compensation depth (CCD), a mid-Cretaceous oceanic hiatus, and Late Cretaceous transgression in the coastal basins. These events seem more or less synchronous in nature and depict north Atlantic paleogeographic developments through the Cretaceous. The mid-Cretaceous events such as deep-sea hiatus and oceanic circulation in the North Atlantic and their extension in the South Atlantic apparently suggest a structural communication in both realms of the Atlantic Ocean, although faunal evidence indicates an earlier surface connection during Aptian to Albian. Finally in the light of published data some paleogeographic aspects are reviewed.

アフリカ北西岸水域におけるマダコの産卵期について

The spawning seasons of common octopus, Octopus vulgaris LAMARCK, off the northwest coast of Africa were determined, using the materials collected by Japanese trawlers during 1967 to 1975. The results obtained are as follows: (1) Most of the males larger than 50cm in total length have spermatophores in all seasons. In the case of females, most of them larger than 70cm in total length are mature, at least in the spawning season, when the smaller ones less than 50cm are usually immature. (2) It is clearly shown that there are two spawning seasons in spring (May-June) and autumn (September) at least in the Cap Blanc region. (3) As for the Villa Cisneros and Nouakchott regions, it is suggested that there are two spawning seasons just as the Cap Blanc region, so far as the materials used are concerned.

アフリカ北西岸水域におけるヨーロッパコウイカ2亜種の地理的分布について

The geographical distribution of two subspecies belonging to Sepia officinalis LINNAEUS off the northwest coast of Africa was examined, using the materials collected by Japaese trawlers. Results obtained are as follows: (1) The southern boundary of Sepia oficinalis oficinalis is in the vicinity of the Cap Vert. (2) The northern boundary of S. o. hierredda is at the latitude of Cap Blanc. (3) S. o. hierredda is found mainly in waters shallower than 50 meters and S. o. officinalis is found in every depth until at least 110 meters off the coast of Mauritania where both subspecies have been inhabiting commonly.

アフリカ北西岸水域におけるヨーロッパコウイカの産卵期について

The spawning season of common cuttlefish, Sepia officinalis officinalis LINNAEUS, off the northwest coast of Africa was estimated in this study, using the materials collected by Japanese trawlers during 1967 to 1975. The results obtained are as follows: (1) Most of the cuttlefish attain sexual maturity at the mantle length of 12-14cm in males and about 14cm in females. (2) Spawning occurs all the year round, but there is a distinct season from April to September. (3) Spawning takes place mainly in coastal waters shallower than 40 meters.

Internal wave climate near the coast of nortwest Africa during JOINT-I

Abstract Current meter measurements from six stations off the coast of northwest Africa are analysed. Decomposition of the data using empirical orthogonal eigenfunctions shows that in depths shallower than 800 m a significant part of the internal wave energy resides in first mode waves that propagate shoreward. Examination of the energy flux and energy density of these waves indicates that: (1) the origin of the internal wave energy appears to be the deep ocean; (2) the energy density of the interval waves increases shoreward in the deep coastal waters subject to a constant energy flux requirement; (3) the energy density in shallow coastal waters is nearly saturated, i.e. the maximum amplitudes are limited by a finite depth and thus the local energy levels are determined by the local Vasala frequency and depth; (4) the energy flux is largely dissipated rather than reflected back out to the deep sea.

Skylab investigation of the upwelling off the northwest coast of Africa

The upwelling off the NW coast of Africa in the vicinity of Cape Blanc was studied in February - March 1974 from aircraft and in September 1973 from Skylab. The aircraft study was designed to determine the effectiveness of a differential radiometer in quantifying surface chlorophyll concentrations. Photographic images of the S190A Multispectral Camera and the S190B Earth Terrain Camera from Skylab were used to study distributional patterns of suspended material and to locate ocean color boundaries. The thermal channel of the S192 Multispectral Scanner was used to map sea-surface temperature distributions offshore of Cape Blanc. Correlating ocean color changes with temperature gradients is an effective method of qualitatively estimating biological productivity in the upwelling region off Africa.

Primary production off the coast of northwest Africa: excretion of dissolved organic matter and its heterotrophic uptake

Abstract The flux of carbon in a eutrophic coastal upwelling region was studied in the Cap Blanc area of northwest Africa from March through May 1974. As part of the primary productivity measurements using radioactive carbon, the release of dissolved organic carbon was measured at 38 stations with 6- and 24-h incubations. The average excretion for the 24-h incubations was 8.16 mg C m −2 h −1 , 8.7% of the total carbon fixed. Excretion covaried with carbon fixation but was not directly influenced by varying nutrient or light conditions. Heterotrophic uptake was computed by means of a carbon mass flux model based on the difference between the rates of accumulation of excretion products in the light and in the dark. This model indicates that bacteria removed 17.8% of the total amount of excreted matter per hour, representing an uptake of 1.45 mg C m −2 h −1 . This is 1.7% of the autotrophic particulate production rate. The total bacterioplankton production available for grazing by the food chain will be less than 1.7% of the autotrophic particulate production, because bacterial respiration and cell maintenance will consume part of the organic uptake. The data indicate that bacterioplankton production has a minor role in the particulate carbon budget of upwelling regions. Conversely, the carbon mass flux model indicates that the heterotrophic bacterial uptake of phytoplankton excretion products regulates the concentration of dissolved organic carbon in the euphotic zone and prevents the accumulation of dissolved material during phytoplankton blooms. In this upwelling region heterotrophs play a major role in determining the chemical character of the water, but they play a minor role in the flux of carbon through the food web.

A study on the mercury content in muscles in the fish family Carangidae from the fishing grounds off the coast of north-west Africa

A study on the mercury content in muscles in the fish family Carangidae from the fishing grounds off the coast of north-west Africa

Heat Budget of the Upper Ocean Under Light Winds

The heat budget of a small region (∼2 km×2 km) near the coast of northwest Africa was investigated during a 3-day period in March 1974 when light winds (∼2 m s−1) occurred. Horizontal advection and diffusion of heat were negligible, and the local change in heat content resulted from the net radiative and evaporative flux at the sea surface. Diurnal heating produced surface temperature ranges of 0.9, 1.1 and 1.4°C for each of the 3 days. The exponential decrease of the diurnal heat wave with depth was used to estimate the vertical eddy thermal conductivity of the upper 10 m; values of approximately 10−3 m−2 s−1 were obtained.

The variability of oceanographic observations off the coast of north-west Africa

During may–June 1969 two sections, 30 nautical miles apart, were worked off the coast of north-west Africa near Cape Blanc. Temperature, salinity, phosphate, silicate and nitrate were observed to a depth of 500 metres. Both sections were worked on three occasions, separated by periods of 50 and 77 hours respectively. Considerable variations in the distribution of the parameters was observed, both between successive surveys of the same section and also between the two sections of the same survey. Observations were also made over a period of 24 hours at two locations on the edge of the continental shelf, and marked variation with time in the distribution of the parameters was recorded at both locations. The nature of the variability is discussed in the light of the upwelling process operating throughout the period of observation.

Primary Production Off the Coast of North-West Africa

Primary Production Off the Coast of North-West Africa

The Yoruba Image of the Witch

Witchcraft, the extra-natural interference in the welfare of the community by women, has long since ceased to be a source of major concern in Western society. In many other areas of the world, however, the witch remains a very active and vital image in the consciousness of the people, This is certainly true for the Yoruba*—a negro group occupying large areas of Nigeria, Dahomey and Togoland along the north-west coast of Africa. With the Yoruba (irrespective of his social level, religion or education), belief in the witch and in her powers is all but universal.

The status of geographical knowledge up to the time of Augustus

The beginning of geography, like that of some other scientific subjects, is more or less shrouded in mystery.1 Perhaps it first originated with the Chinese, then came by the way of India and Babylonia to Egypt, and from there to the Greeks and Romans.2 The Graeco-Roman civilization was the center of exploration which has revealed the world and has rendered possible the present worldwide civilization.3 It is true that the Phoenicians were the first nation of discoverers of whom there is definite record.4 Their ships sailed in all the Mediterranean waters and in those of the Black Sea. They discovered Spain about 1050 B.C.,6 and brought from there many of the metals and native products. As early as 1000 B.C. traders came to them from India and from lands beyond the Red Sea.6 Both Hebrew and Greek literature represent them as daring navigators capable of conducting long voyages and bringing back the products of distant countries.7 Tyre, one of the principal Phoenician cities, is mentioned in the Bible as a mart of the nations.8 By the time of Herodotus (484-424 B.C.) the Phoenicians had established colonies on the northwest coast of Africa, had brought tin from Cornwall, and had made valuable contributions to the exact knowledge of geography by their travels. They sailed to the Malabar coast of India and to Ultima Thule. Some historians claim that this latter region is what is now known as the Shetland Islands ;9 others suggest that Iceland might have been meant ;10 and yet others think that it might have been the southern coast of Norway. In all these explorations the Phoenicians were strictly commercial people. They had only the desire for personal or national gain.12