ALBERT

Description: Benthic foraminifera from surface Sediments of the Ross Sea were studied to determine modern distributions of important assemblages. Factor analysis of the raw data distinguished nine significant factor assemblages which account for 86% of the raw data. These factor assemblages provide a means of understanding modern oceanographic and ecologic conditions because they show the response of this faunal group to different environments. Environmental conditions are in turn controlled by the modern climatic regime of the region. Four benthic assemblages from the relatively shallow (500 to 700 m) eastern Ross Sea Continental shelf are predominantly arenaceous. This may be because the relatively late seasonal breakup of pack ice inhibits productivity in the surface waters and permits a buildup of CO, thus causing the CCD to occur at shallow depths. On the Western part of the Continental shelf, three assemblages are composed primarily of calcareous species even though water depths are often greater there than they are in the east. One of these calcareous assemblages occurs in samples from water depths as great as 755 m in the southwestern part of the region, below the CCD as defined for the Ross Sea by previous workers. We relate this depressed CCD to early seasonal breakup of pack ice in the Western Ross Sea. Within the eastern arenaceous and Western calcareous regions on the Continental shelf, distributions of benthic assemblages are probably related to water depth and other ecologic variables. Two benthic assemblages from the Continental slope north of the Ross Sea also are calcareous. We attribute their distributions to high rates of productivity in the overlying surface waters, where the interface between eastward-flowing Circumpolar Deep Water and Ross Sea water masses is marked by a narrow zone of intense upwelling.

Description: Foraminiferal evidence from the eastern equatorial Pacific and from the North Atlantic indicates that the dissolution of deep-sea carbonates was intensified during interglacials rather than during glacials, in contrast to widespread opinion. Pleistoccne dissolution cycles introduce a systematic bias into the Interpretation of calcareous fossil assemblages near and below the lysocline zone.

Description: Spirula spirula has stimulated considerable interest since it was first discovered. It is a member of one of the two genera of sepioids to frequent oceanic water (the other being Heteroteuthis); it has a unique spiral shell which acts as a buoyancy mechanism and can withstand considerable pressure (Denton, Gilpin-Brown & Howarth, 1967); and, until the capture by the Danish Oceanographical expeditions it was considered very rare, only 12 specimens having been captured. The Dana expeditions caught 193 individuals from 1909 to 1931 and these were described by Kerr (1931) and Bruun (1943,1955). Most of these were caught in the waters around the Canary Islands of the North Atlantic. Bruun (1943) arranged the specimens according to month and size and claimed that two size groups could be distinguished. The specimens were taken over a wide geographical area, in several years and during the months of February (1 specimen), March (40), April (3), May (8), June (1), August (1) and October (23). His conclusion concerning growth depends entirely upon his decision to split the March sample into two year-groups; those above 1.9 cm in ventral mantle length he put in a separate year-class to those below 1.9 cm in ventral mantle length. This division was arbitrary and, one suspects, based on a belief that a one-year life-span was likely. Clearly the growth of Spirula requires further study based on a larger collection and the present paper is an attempt to fulfil this need.

Description: This review is intended to cover the principal developments that have occurred within the last six years in the paleomagnetic study of marine sediments. Recent work utilizing the reflecting-light microscope indicates that detrital high-temperature Fe-Ti oxides are probably responsible for most of the magnetic remanence in marine sediments. These minerals possess a spectrum of coercivities that makes it necessary to use alternating-field—demagnetization techniques to isolate stable components. It is possible to use the standard magnetic stratigraphy for the last 4 m.y. of earth history derived from terrestrial lavas. Using the ages of the magnetic boundaries from this time scale it is possible by extrapolation and interpolation to better determine the ages of the major events. The ages of these events in increasing age are Jaramillo, 0.87 to 0.92 m.y.; Olduvai, 1.71 to 1.86 m.y.; Kaena, 2.82 to 2.90 m.y.; Mammoth, 3.0 to 3.085 m.y.; Cochiti, 3.72 to 3.82 m.y.; Nunivak, 3.97 to 4.14 m.y.; ‘c’ event of the Gilbert series, 4.33 to 4.65 m.y. Through the use of long cores from the central Pacific and through correlation using fossil datums, it has been possible to extend the magnetic stratigraphy back to the upper middle Miocene to magnetic epoch 5. It is concluded that very short magnetic events are probably short-term excursions of the field and not true magnetic events. It is shown that the field of the earth averages to an axial-dipole field within a period of 27,000 years and that the field over the last two million years has acted as a geocentric axial dipole. The evidence shows that when reversals of the dipole occur, the values of the reversed inclination are not significantly different from the normal values. The use of magnetic stratigraphy in marine geology has opened up a new era in study of sedimentary processes and evolution of marine organisms.

Description: The application of plagioclase geothermometry to plagioclase-bearing volcanic ash layers and to the glassy margins of pillow basalts from the fast-spreading East Pacific rise, the moderately spreading Gorda and Juan de Fuca ridges, and the slow-spreading mid-Atlantic ridge has shown that magma temperatures, as well as average An contents of plagioclases, are negatively correlated with spreading rates. A detailed investigation of the major element chemistry of volcanic glasses from each of these areas suggests that the observed consistent element-element covariances among individual populations of samples have been caused by fractional crystallization of the magmas. The regularity of chemical variation and the similarity of magma temperatures within each population of samples suggest that magmas ascending from beneath each ridge have had similar evolutionary histories. Vector analysis of the chemical data of all samples of volcanic glasses indicate that each population of samples from each of the spreading centers is chemically distinct, even though all samples have been subjected to similar amounts of fractional crystallization. The compositional distinctiveness of each population of oceanic tholeiites probably reflects differences in the depths at which the magmas were generated. Calculated magma temperatures and geothermal gradients calculated from published heat flow measurements can be used to estimate depths of magma generation of about 16 km beneath the East Pacific rise and about 23 km beneath the mid-Atlantic ridge.

Description: We present a plate kinematic evolution of the South Atlantic which is based largely on the determination of the equatorial fracture zone trends between the African and South American continental margins. Four main opening phases are dated by oceanic magnetic anomalies, notably MO, A34, and A13, and are correlated with volcanism and tectonic events on land around the South Atlantic Ocean. The Ceara and Sierra Leone rises are probably of oceanic origin and were created 80 m.y. ago or later in their present-day positions with respect to South America and Africa.

Description: This paper concerns the linear response of the ocean to forcing at a specified frequency and wave number in the absence of mean currents. It discusses the details of the forcing function, the general properties of the equations of motion, and possible simplifications of these equations. Two representations for the oceanic response to forcing are described in detail. One solution is in terms of the normal modes of the ocean. The vertical structure of these modes corresponds to that of the barotropic and baroclinic modes; their latitudinal structure corresponds to that of inertia‐gravity and Rossby waves. These waves are eigenfunctions of Laplace's tidal equations (LTE) with the frequency as eigenvalue. The description in terms of vertically standing modes is particularly useful if the forcing is nonlocal, because only these modes can propagate into undisturbed regions. The principal result is that it is extremely difficult for baroclinic (but not barotropic) disturbances to propagate horizontally away from a forced region. Instabilities of the Gulf Stream excite disturbances that are confined to the immediate neighborhood of the current; disturbances due to instabilities of equatorial currents do not propagate far latitudinally. A second representation of the oceanic response to forcing is in terms of vertically propagating, or vertically trapped, latitudinal modes. These modes are eigenfunctions of LTE with the equivalent depth h (not the frequency) as eigenvalue. Both positive and negative eigenvalues h are necessary for completeness. The modes with h 〉 0 consist of an infinite set of inertia‐gravity waves and a finite set of Rossby waves which either propagate vertically or form vertically standing modes. The latitudinally gravest modes are equatorially trapped and have been observed in the Atlantic and Pacific oceans. The modes with h 〈 0 are necessary to describe the oceanic response to nonresonant forcing. In the vertical this response attenuates with increasing distance from the forcing region. Because of the shallowness of the ocean the large eastward traveling atmospheric cyclones in mid‐latitudes and high latitudes force a response down to the ocean floor. Interaction with the bottom topography will result in smaller‐scale disturbances and will affect the frequency spectrum of the response when bottom‐trapped waves are excited.

Description: Morphological characters, interrelations, evolutionary trends, synonymies, Stratigraphie and paleogeographic distribution of 15 species here included in Globigerinatheka are discussed and illustrated by line drawings and SEM mircographs. In order to stress their interrelations, all taxa—with the exception of G. semiinvoluta—are given subspecific rank in a trinomial System. Holotypes and some additional types of the taxa discussed, which originally were published at widely varying magnifications, are reproduced at a uniform scale to facilitate their comparison. By this procedure alone the four species subconglobata, indes, mexicana and semiinvoluta become clearly distinct. The final chamber/bulla problem, of some importance in the genus, is discussed and illustrated. Evidence is given that G. semiinvoluta is a valid species, and not a synonym of G. mexicana mexicana. Its variability is demonstrated by a series of SEM micrographs. One subspecies, G. subconglobata luterbacheri, is described as new.

Description: The distinguishing features of the common squid of British waters, Loligo forbesi, are summarized, and contrasted with those of L. vulgaris. The life-cycle and growth of L. forbesi are described, based on samples from trawl catches off Plymouth. This species seems to be an annual - young squid first appear in the trawl in late May, when their length is about 10 or 11 cm. Subsequent growth is rapid, and the males reach 30 cm and the females 25 cm by November. Spawning takes place mainly in December-January, but may continue into the spring. Neither sex survives beyond a single spawning season. Hatching of the spawn probably takes 30–40 days, and if the young squid taken in the trawl in late May hatched in the early part of the same year, a growth rate of about 25 mm/month would be required. Known growth rates for other species of Loligo are about 20 mm/month, so that indicated for L. forbesi does not seem to be impossibly high. The life-cycle is summarized in Fig. 8. There is also a summer spawning population, which grows to a rather smaller size at maturity, and which also seems to be annual. During the summer L. forbesi ranges throughout the English Channel and southern North Sea, particularly in inshore areas. In October the squid migrate farther offshore and tend to occupy the western part of the Channel. Values for total weight of squid/2 h trawl are given, on a monthly basis, for 1966–9. The largest quantities are usually taken in October and November, the highest single figure being 30.54 kg/2 h trawl, in November 1967.