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Formation of oceanic ridges
Oceanographic Abstracts
1029
BISCAYE PIERRE E., 1964. Mineralogy and sedimentation o f recent deep-sea clay in the Atlantic Ocean and adjacent seas and oceans. GeoL Soc., Am. Bull., 76 (7): 803-832. Semiquantitative mineral analysis has been done by X-ray diffraction on the < 2 ~- and 2-20 ~-size fractions of approximately five hundred Recent deep-sea core samples from the Atlantic, Antarctic, western Indian Oceans, and adjacent seas. Relative abundances of montmorillonite, illite, kaolinite, chlorite, gibbsite, quartz, amphibole, clinoptilolite-heulandite (?), and pyrophyllite(?) were determined. Mixed-layer clay minerals, reid-spars, and dolomite were also observed but not quantitatively evaluated. From the patterns of mineral distribution, the following conclusions appear warranted: Most Recent Atlantic Ocean deep-sea clay is detritus from the continents. The formation of minerals in situ on the ocean bottom is relatively unimportant in the Atlantic but may be significant in parts of the southwestern Indian Ocean. Mineralogical analysis o f the fine fraction of Atlantic Ocean deep-sea sediments is a useful indicator of sediment provenance. Kaolinite, gibbsite, pyrophyllite, mixed-layer minerals, and chlorite contribute the most unequivocal provenance information because they have relatively restricted loci of continental origin. Topographic control over mineral distribution by the Mid-Atlantic Ridge in the North Atlantic Ocean precludes significant eolian transport by the jet stream and emphasizes the importance of transport to and within that part of the deep-sea by processes operative at or near the sediment-water interface. Transport of continent-derived sediment to the equatorial Atlantic is primarily by rivers draining from South America and by rivers and wind from Africa. The higher proportion of kaolinite and gibbsite in deep-sea sediments adjacent to small tropical South American rivers reflects a greater intensity of lateritic weathering than is observed near the mouths of the larger rivers. This may be explained by a greater variety ofpedogenic conditions in the larger drainage basins, resulting in an assemblage with proportionately less lateritic material in the detritus transported by the larger rivers despite their quantitatively greater influence on deep-sea sediment accumulation. In the South Atlantic Ocean, the fine-fraction mineral assemblage of surface sediment in the Argentine Basin is sufficiently unlike that adjacent to the mouth of the Rio de la Plata to preclude it as a major Recent sediment source for that basin. The southern Argentine Continental Shelf, the Scotia Ridge, and the Weddell Sea are mineralogically more likely immediate sources. Transport from the Weddell Sea by the Antarctic Bottom Water may be responsible for the northward transport of fine-fraction sediment along parts of the western South Atlantic as far north as the Equator. BLANCHARD RICHARD L., 1965. U 234/U 238 ratios in coastal marine waters and calcium carbonates. J. geophys. Res., 70 (16): 4055--4061. Water and live molluscan shell samples were collected simultaneously at seven locations on the seacoast of the United States. Samples of silt, water, and shells from an estuary were also included in the study. The water samples were analyzed for U 2~8, Ll~aa, calcium, and salinity; the shell samples were analyzed for U zaa, U zaa, calcium, and crystal structure. All water samples, regardless of salinity or total uranium content, were found to have uranium activity ratios, AvZ2a/Av 23s, within the experimental uncertainty o f the 1-15 value accepted for an oceanic environment. The results indicate that the normally higher uranium activity ratio of rivers does not increase the ratio o f coastal waters above the 1-15 oceanic value. The activity ratios of all except two shell samples analyzed were similar to those o f the surrounding seawater and to the oceanic I. 15 value. The application of the results of the study to the determination o f geologic age via uranium-uranium daughter equilibrium is discussed. BOOTH E., 1965. The manurial value o f seaweed. Botanica Marina, 8 (1): 138-143. The use of seaweed products as manure is discussed with reference to nutrient content, the presence of compounds known to affect plant growth or the physical condition of the soil and the effect of algal chemicals on plant diseases. The recent discovery that chitin, laminarin and seaweed have a mycolytic effect o n certain phytopathogenic fungi, together with the failure of analytical methods to explain the nutritional value of organic manures, has revived interest in the biochemical study of the traditional manures. Certain agricultural research which appears to be related to some of the research on seaweed is also included. Boar M. H. P., 1965. Formation of oceanic ridges. Nature, Lond. 207 (4999): 840-843. The low-density underlying rocks causing the uplift of the oceanic ridges and the western United States lie in the upper mantle, and substantially result from partial fusion, although other causes such as serpentinization may contribute. The evidence leading to this conclusion comes from a combination o f geological, geophysical and geochemical discoveries of recent years, and particularly the present burst o f oceanographical research. When pieced together, this evidence suggests rejection of other hypotheses such as crust-mantle mix and solid-solid phase changes as the major cause on the assumption that a single mechanism is of prime importance throughout the whole system of ocean ridges. The hypothesis of partial fusion, however, seems to be consistent with all the lines of evidence. The only mechanism known for causing magma generation on such a large scale depends on the reduction of confining pressure in an upwelling convection current in the mantle. Such convection currents appear to rise beneath the oceanic ridges, causing their volcanism and uplift.
1030
Oceanographic Abstracts
The hypothesis is equally applicable to uplifts such as the East Pacific Rise which have taken place without associated horizontal movements, and to the Mid-Atlantic Ridge where in addition to the vertical uplift new oceanic crust may be in the process of formation. BOUMA ARNOLD H., 1964. Notes on X-ray interpretation of marine sediments. Mar. GeoL, 2 (4): 278-309. X-ray radiography is a technique recently introduced in the study of sediments. The method is very useful for analysing details o f primary and secondary sedimentary structures or to detect their presence in unconsolidated as well as in consolidated deposits. Prints of radiographs made from vertical slices of samples collected in Recent marsh, submarine canyons and estuarine environments are used to discuss the interpretation of the visible structures. BRADNER H., J. G. DODDS and R. E. FOULKS, 1965. Investigation ofmicroseism sources with oceanbottom seismometers. Geophysics, 30 (4): 511-526. Recordings to depths o f 5 km have been made on the Pacific Ocean bottom with self-rising internally recording seismometers. Simultaneous recordings have been made at land stations. The oceanbottom noise spectrum is between one and five orders of magnitude higher power than the land spectrum in the region from 0'1 to 9.0 cps. Coherence between two simultaneous instruments separated one-quarter kilometer is above the 95 percent confidence level from 0.1 cps to 0'6 cps. Attempts to associate narrow-beam Love and Rayleigh peaks with large storm-generating areas or with heavy swell striking shore have not produced consistent results. Although some records show the bulk of the microseism peak energy in well-defined modes, the energy is carried in different modes at different times and locations. Some of our data fit a model of microseism generation in a 100-mile strip, by a statistical superposition of incident waves and waves reflected from shore; and the subsequent conversion of the energy to Rayleigh and Love modes propagating away from the generation zone. However, the shapes of the mid-ocean spectra strongly imply additional sources far from shorelines or recognized storms, unless microseisms attenuate far less in the ocean than on land. BREDER C. M. JR., 1965. Vortices and fish schools. Zoologica, N. Y. ZooL Soc., 50 (2): 97-114. Since fishes produce vortices when swimming and leave a trail of dying vortices after them, these become a factor in the environment of those fishes accompanying them. This is of special significance to the structure of the fish school. The side-to-side spacing o f fishes in a school is usually just a little over twice the distance from the side of a fish to the outer edge of the trail o f vortices in the area of their production, which insures their integrity until the fishes have left them behind. As the maintenance of the integrity o f these vortices is important to the efficiency of the fish's locomotor efforts, this may be the controlling factor that determines how closely fishes in a school approach each other. There is usually continual shifting of positions o f fish within a school which is evidently partly controlled by accidental encounters with parts of the vortices that reduce swimming efficiency. This continual adjustment by the fishes makes possible the continued existence o f the group. The range in sizes o f fishes that may comprise a stable school appears to be limited to something closer than 1 to 0"6, taking the largest individual as unity. Also evidently responsible for some part of the continual shifting is the fact that the fish are not precisely o f one size, nor are they of identical swimming ability or degree of fatigue, which produces somewhat of a conflict between individually perferred swimming speed and the attempt of each fish to keep close to its group. Since vortices appear in various natural conditions from many sources, fishes make appropriate adjustments to them, especially noticeable in certain rates o f flow where a stream may be filled with a mixture of several Kfirrnfin vortex trails, forcing fishes which venture into it to take a marked zigzag course, both avoiding adverse flow and benefiting from advantageous flow, from one sheltered place to another. Closed figure fish schools, the so-called fish mills, may be initiated by both extrinsic and intrinsic causes, the first and classic cause being something that turns the forwardly placed members so they see the trailing members and proceed to follow them. The second is associated with the structure of the school involving viscous shear and showing behaviour very like that of a viscid fluid. The disruption of schools by violent means is usually followed by immediate re-formation, while disruption by specialized feeding methods or special feeding techniques is followed by reformation only after the full completion of the special action involved. Consideringthe fish school as a system of interacting parts, the relations within it cannot be linear, for if they were, the reactions of a school as a whole would, on a basis of response to disturbances, be notably different. Similarities and differences between the vorticular systems found in association with swimming fishes and the vortices found in other situations are discussed. Included are comments on the theoretical size limits of schools, the nature of their redundancy and the elements of attraction and repulsion present. BREWER P. G., J. P. Rzta~v and F. CutJ~IN, 1965. The chemical composition of the hot salty water from the bottom o f the Red Sea. Deep-Sea Res., 12 (4): 497-503. Samples o f a hot salty water discovered in a deep basin in the Red Sea have been analysed for dissolved gases and major and minor constitutents. It is shown that this water is different in composition from ordinary sea water and some possible explanations o f its composition are discussed.
1029
BISCAYE PIERRE E., 1964. Mineralogy and sedimentation o f recent deep-sea clay in the Atlantic Ocean and adjacent seas and oceans. GeoL Soc., Am. Bull., 76 (7): 803-832. Semiquantitative mineral analysis has been done by X-ray diffraction on the < 2 ~- and 2-20 ~-size fractions of approximately five hundred Recent deep-sea core samples from the Atlantic, Antarctic, western Indian Oceans, and adjacent seas. Relative abundances of montmorillonite, illite, kaolinite, chlorite, gibbsite, quartz, amphibole, clinoptilolite-heulandite (?), and pyrophyllite(?) were determined. Mixed-layer clay minerals, reid-spars, and dolomite were also observed but not quantitatively evaluated. From the patterns of mineral distribution, the following conclusions appear warranted: Most Recent Atlantic Ocean deep-sea clay is detritus from the continents. The formation of minerals in situ on the ocean bottom is relatively unimportant in the Atlantic but may be significant in parts of the southwestern Indian Ocean. Mineralogical analysis o f the fine fraction of Atlantic Ocean deep-sea sediments is a useful indicator of sediment provenance. Kaolinite, gibbsite, pyrophyllite, mixed-layer minerals, and chlorite contribute the most unequivocal provenance information because they have relatively restricted loci of continental origin. Topographic control over mineral distribution by the Mid-Atlantic Ridge in the North Atlantic Ocean precludes significant eolian transport by the jet stream and emphasizes the importance of transport to and within that part of the deep-sea by processes operative at or near the sediment-water interface. Transport of continent-derived sediment to the equatorial Atlantic is primarily by rivers draining from South America and by rivers and wind from Africa. The higher proportion of kaolinite and gibbsite in deep-sea sediments adjacent to small tropical South American rivers reflects a greater intensity of lateritic weathering than is observed near the mouths of the larger rivers. This may be explained by a greater variety ofpedogenic conditions in the larger drainage basins, resulting in an assemblage with proportionately less lateritic material in the detritus transported by the larger rivers despite their quantitatively greater influence on deep-sea sediment accumulation. In the South Atlantic Ocean, the fine-fraction mineral assemblage of surface sediment in the Argentine Basin is sufficiently unlike that adjacent to the mouth of the Rio de la Plata to preclude it as a major Recent sediment source for that basin. The southern Argentine Continental Shelf, the Scotia Ridge, and the Weddell Sea are mineralogically more likely immediate sources. Transport from the Weddell Sea by the Antarctic Bottom Water may be responsible for the northward transport of fine-fraction sediment along parts of the western South Atlantic as far north as the Equator. BLANCHARD RICHARD L., 1965. U 234/U 238 ratios in coastal marine waters and calcium carbonates. J. geophys. Res., 70 (16): 4055--4061. Water and live molluscan shell samples were collected simultaneously at seven locations on the seacoast of the United States. Samples of silt, water, and shells from an estuary were also included in the study. The water samples were analyzed for U 2~8, Ll~aa, calcium, and salinity; the shell samples were analyzed for U zaa, U zaa, calcium, and crystal structure. All water samples, regardless of salinity or total uranium content, were found to have uranium activity ratios, AvZ2a/Av 23s, within the experimental uncertainty o f the 1-15 value accepted for an oceanic environment. The results indicate that the normally higher uranium activity ratio of rivers does not increase the ratio o f coastal waters above the 1-15 oceanic value. The activity ratios of all except two shell samples analyzed were similar to those o f the surrounding seawater and to the oceanic I. 15 value. The application of the results of the study to the determination o f geologic age via uranium-uranium daughter equilibrium is discussed. BOOTH E., 1965. The manurial value o f seaweed. Botanica Marina, 8 (1): 138-143. The use of seaweed products as manure is discussed with reference to nutrient content, the presence of compounds known to affect plant growth or the physical condition of the soil and the effect of algal chemicals on plant diseases. The recent discovery that chitin, laminarin and seaweed have a mycolytic effect o n certain phytopathogenic fungi, together with the failure of analytical methods to explain the nutritional value of organic manures, has revived interest in the biochemical study of the traditional manures. Certain agricultural research which appears to be related to some of the research on seaweed is also included. Boar M. H. P., 1965. Formation of oceanic ridges. Nature, Lond. 207 (4999): 840-843. The low-density underlying rocks causing the uplift of the oceanic ridges and the western United States lie in the upper mantle, and substantially result from partial fusion, although other causes such as serpentinization may contribute. The evidence leading to this conclusion comes from a combination o f geological, geophysical and geochemical discoveries of recent years, and particularly the present burst o f oceanographical research. When pieced together, this evidence suggests rejection of other hypotheses such as crust-mantle mix and solid-solid phase changes as the major cause on the assumption that a single mechanism is of prime importance throughout the whole system of ocean ridges. The hypothesis of partial fusion, however, seems to be consistent with all the lines of evidence. The only mechanism known for causing magma generation on such a large scale depends on the reduction of confining pressure in an upwelling convection current in the mantle. Such convection currents appear to rise beneath the oceanic ridges, causing their volcanism and uplift.
1030
Oceanographic Abstracts
The hypothesis is equally applicable to uplifts such as the East Pacific Rise which have taken place without associated horizontal movements, and to the Mid-Atlantic Ridge where in addition to the vertical uplift new oceanic crust may be in the process of formation. BOUMA ARNOLD H., 1964. Notes on X-ray interpretation of marine sediments. Mar. GeoL, 2 (4): 278-309. X-ray radiography is a technique recently introduced in the study of sediments. The method is very useful for analysing details o f primary and secondary sedimentary structures or to detect their presence in unconsolidated as well as in consolidated deposits. Prints of radiographs made from vertical slices of samples collected in Recent marsh, submarine canyons and estuarine environments are used to discuss the interpretation of the visible structures. BRADNER H., J. G. DODDS and R. E. FOULKS, 1965. Investigation ofmicroseism sources with oceanbottom seismometers. Geophysics, 30 (4): 511-526. Recordings to depths o f 5 km have been made on the Pacific Ocean bottom with self-rising internally recording seismometers. Simultaneous recordings have been made at land stations. The oceanbottom noise spectrum is between one and five orders of magnitude higher power than the land spectrum in the region from 0'1 to 9.0 cps. Coherence between two simultaneous instruments separated one-quarter kilometer is above the 95 percent confidence level from 0.1 cps to 0'6 cps. Attempts to associate narrow-beam Love and Rayleigh peaks with large storm-generating areas or with heavy swell striking shore have not produced consistent results. Although some records show the bulk of the microseism peak energy in well-defined modes, the energy is carried in different modes at different times and locations. Some of our data fit a model of microseism generation in a 100-mile strip, by a statistical superposition of incident waves and waves reflected from shore; and the subsequent conversion of the energy to Rayleigh and Love modes propagating away from the generation zone. However, the shapes of the mid-ocean spectra strongly imply additional sources far from shorelines or recognized storms, unless microseisms attenuate far less in the ocean than on land. BREDER C. M. JR., 1965. Vortices and fish schools. Zoologica, N. Y. ZooL Soc., 50 (2): 97-114. Since fishes produce vortices when swimming and leave a trail of dying vortices after them, these become a factor in the environment of those fishes accompanying them. This is of special significance to the structure of the fish school. The side-to-side spacing o f fishes in a school is usually just a little over twice the distance from the side of a fish to the outer edge of the trail o f vortices in the area of their production, which insures their integrity until the fishes have left them behind. As the maintenance of the integrity o f these vortices is important to the efficiency of the fish's locomotor efforts, this may be the controlling factor that determines how closely fishes in a school approach each other. There is usually continual shifting of positions o f fish within a school which is evidently partly controlled by accidental encounters with parts of the vortices that reduce swimming efficiency. This continual adjustment by the fishes makes possible the continued existence o f the group. The range in sizes o f fishes that may comprise a stable school appears to be limited to something closer than 1 to 0"6, taking the largest individual as unity. Also evidently responsible for some part of the continual shifting is the fact that the fish are not precisely o f one size, nor are they of identical swimming ability or degree of fatigue, which produces somewhat of a conflict between individually perferred swimming speed and the attempt of each fish to keep close to its group. Since vortices appear in various natural conditions from many sources, fishes make appropriate adjustments to them, especially noticeable in certain rates o f flow where a stream may be filled with a mixture of several Kfirrnfin vortex trails, forcing fishes which venture into it to take a marked zigzag course, both avoiding adverse flow and benefiting from advantageous flow, from one sheltered place to another. Closed figure fish schools, the so-called fish mills, may be initiated by both extrinsic and intrinsic causes, the first and classic cause being something that turns the forwardly placed members so they see the trailing members and proceed to follow them. The second is associated with the structure of the school involving viscous shear and showing behaviour very like that of a viscid fluid. The disruption of schools by violent means is usually followed by immediate re-formation, while disruption by specialized feeding methods or special feeding techniques is followed by reformation only after the full completion of the special action involved. Consideringthe fish school as a system of interacting parts, the relations within it cannot be linear, for if they were, the reactions of a school as a whole would, on a basis of response to disturbances, be notably different. Similarities and differences between the vorticular systems found in association with swimming fishes and the vortices found in other situations are discussed. Included are comments on the theoretical size limits of schools, the nature of their redundancy and the elements of attraction and repulsion present. BREWER P. G., J. P. Rzta~v and F. CutJ~IN, 1965. The chemical composition of the hot salty water from the bottom o f the Red Sea. Deep-Sea Res., 12 (4): 497-503. Samples o f a hot salty water discovered in a deep basin in the Red Sea have been analysed for dissolved gases and major and minor constitutents. It is shown that this water is different in composition from ordinary sea water and some possible explanations o f its composition are discussed.