ALBERT

Description: Males of Eledone cirrhosa grow to a size little over 600 g and normally have well-developed, and presumably active, reproductive organs from about 200 g upwards. Total weight of the genital bag is well correlated with total body weight (r= 0·906). Growth of the testis precedes that of the spermatophoric sac, and the size of neither of these reproductive components is predictable from body weight. The sizes of these organs and the estimated number and length of stored spermatophores are given for 100 g intervals of total body weight. No evidence was obtained for a seasonal trend in male maturity.

Description: Samples collected at hourly intervals on May 18–19, 1980, at three sites 200 km downwind from Mount St. Helens, have made possible a detailed reconstruction of the conditions that contribute to the compositional heterogeneity of mineral and glass components observed in distal tephra layers. The air fall tephra deposited at the sites during the first 7 hours of the May 18 eruption is mostly coarse grained, microlite-rich, nonjuvenile glass and feldspar. Grain-size maxima in this initial tephra can be related to the cataclysmic blast at 0832 and a subsequent pulse of the eruption at 1200. Juvenile, microlite-free glass increases in relative abundance at the sampling sites beginning at about 1900. Such a change between nonjuvenile and juvenile tephra can be related to a 5-km increase in column height associated with the last major pulse of the eruption which occurred at 1700 at the volcano. Electron microprobe study of both microlite-rich and microlite-free pumice in the time series samples reveals significant compositional differences. Interstitial glass in nonjuvenile pumice deposited during the first few hours at the sampling sites is enriched in SiO2 and K2O and depleted in TiO2, FeO*, and MgO relative to juvenile glass. By comparison, major element composition of the least evolved juvenile glass sampled during the last several hours of the eruption displays a slight trend toward less evolved composition. Least squares calculations suggest that the more evolved character of the nonjuvenile glass can be explained by greater fractional crystallization brought about by enhanced cooling in a cryptodome prior to eruption, whereas the temporal changes observed in juvenile glass composition during the last several hours of the eruption suggest the presence of a small, slightly zoned magma chamber at depth. Electron microprobe study of glass-coated ilmenites, magnetites, and plagioclases provides the following estimates of the physical conditions in this reservoir: 865°±50°C, PH2O = 2.2 kbar and -log ƒO2 = 11.7. Analyses of bulk pumice, glass and selected mineral phases from May 25, June 12, July 22, and October 16–18 pumices erupted from Mount St. Helens indicate that the bulk pumice (magma) compositions have become slightly more andesitic with time, while mineral and co-existing glass compositions have changed significantly in post-May 18 eruptions with both being more highly evolved than those associated with the May 18 eruption. An application of the magnetite-ilmenite geothermometer to June 12 and July 22 samples indicates temperatures of 919°±30°C and 930°±50°C, respectively. Least squares calculations suggest that such evolved post-May 18 glass and mineral phases can be derived by fractional crystallization of a magma composition like bulk May 18 pumice into approximately 50% crystals and 50% residual liquid. Such partitioning between crystals and residual liquid appears to have occurred on the scale of centimeters and is interpreted as a consequence of accelerated crystallization under reduced water pressure.

Description: We present chemical data on magmatically heterogeneous pyroclastic deposits of late Quaternary age erupted from zoned magma systems underlying Tenerife (Canary Islands), Sao Miguel and Faial (Azores), and Vesuvius. The most fractionated magmas present at each centre are respectively Na-rich phonolite, trachyte, and K-rich phonolite. Within any one deposit, chemical variation is either accompanied by changes in the phenocryst assemblage (petrographic zonation) or is largely manifested in trace element abundances, unaccompanied by any petrographic change (occult zonation). Zoning is analogous to that in calc-alkaline systems where the most fractionated products are high-silica rhyolites. When a range of magma types are considered, a correlation emerges between roofward depletion of trace elements (especially REE) in the zoned system and compatability of those same trace elements in the accessory phenocryst phases present. Thus, allanite- or chevkinite-bearing rhyolitic systems are light-REE depleted roofwards, the sphene-bearing Tenerife system is middle-REE depleted roofwards, the melanite-bearing Vesuvius system is heavy-REE depleted roofwards, while the Azores systems, which lack these phases, display roofward REE enrichment. Therefore, the behaviour of trace elements may in each case be explained by fractionation of observed phenocryst assemblages. The resemblance between features of zoned magma systems and published work on the dynamic consequences of cooling saturated aqueous solutions prompts us to suggest that sidewall crystallization and consequent boundary-layer uprise to form a capping layer at top of the system may be a plausible mechanism for the generation of both petrographic and occult zonation. Reverse zoning occurs among the first-erupted tephra of some deposits, demonstrating that the most highly differentiated magma available is not always the first to be tapped during an eruption from a zoned system.

Description: Changes in the relative size of the ovary, oviducal glands and eggs are described for Eledone cirrhosa captured from the North Sea off Aberdeen over a 3 year period (N = 488). The analysis is based only on freshly caught animals, excluding those held in aquarium conditions (〉 5 days). Ovary enlargement and egg size estimates are used as indices of sexual maturity. Between 0–15% and 18–95% of total body weight is contributed by the ovary. Maximum egg length in the ovary ranges up to 7 mm. On these criteria, sexual maturation typically occurs at body sizes between 400–1000 g although some animals of 1000–1200 g are found showing no evidence of ovary enlargement. The majority of the monthly sample is always immature but maturation can apparently occur at almost any time of the year. Increase in mean ovary index and mean values for egg size are strongly seasonal and indicate a peak incidence of sexual maturity over 2–3 months in the July-September period. Spawning is presumed to follow within 1 month. Estimates of the fecundity of the females, based on the egg sample from the ovary, range from 2·2 × 103 to 55 × 10 3 eggs with a mean of 11 × 10 3 and a mode of 7·5 × 10 3 eggs.

Description: Female Eledone cirrhosa held in aquarium conditions for periods of time of five daysand over show relatively enlarged ovary sizes. Values for ovary index considerably exceed thoseof freshly caught animals and the incidence of the final stage of maturity, in which eggs pack the oviducts, is greater. A comparison of maturity indices for fresh and aquarium males was inconclusive. The range of factors associated with aquarium conditions is briefly reviewed and it is concluded that studies of cephalopod reproductive maturation must distinguish fresh and aquarium animals. Introduction External factors effective in inducing sexual maturation in cephalopods have been suggested several times. The influence of the absence of light has been implicated since the experiments of Wells & Wells (1959) showed that blinded Octopus vulgar is matured precociously. An effect of short day length in stimulating the optic glands of Sepia has been found by Defretin & Richard (1967) and Richard (1967) but this is not clearly the case for Octopus (Buckley, 1977). Octopuses kept in aquarium conditions for lengthy periods are said to have larger relative gonad sizes than those fresh from the sea (Wells & Wells, 1975). One of the factors associated with aquarium conditions is often a degree of starvation, and this circumstance alone is held to be a factor in inducing precocious sexual maturation in Eledone (Mangold & Boucher-Rodoni, 1973). In the course of recent studies on the growth and reproduction of Eledone cirrhosa from the North Sea (Boyle & Knobloch, 1982,1983,1984) animals which had remained in aquarium conditions for 5 days or over were separated from the analysis.

Description: The well-known caldera of Thira (Santorini), Greece, was not formed during a single eruption but is composed of two overlapping calderas superimposed upon a complex volcanic field that developed along a NE trending line of vents. Before the Minoan eruption of 1400 B.C., Thira consisted of three Java shields in the northern half of the island and a flooded depression surrounded by tuff deposits in the southern half. Andesitic lavas formed the overlapping shields of the north and were contemporaneous with and, in many places, interbedded with the southern tuff deposits. Although there appears to be little difference between the composition of magmas erupted, differences in eruption style indicate that most of the activity in the northern half of the volcanic field was subaerial, producing lava flows, whereas in the south, eruptions within a flooded depression produced a sequence of mostly phreatomagmatic tuffs. Many of these tuffs are plastered onto the walls of what appears to have been an older caldera, most probably associated with an eruption of rhyodacitic tephra 100,000 years ago. The Minoan eruption of about 1400 B.C. had four distinct phases, each reflecting a different vent geometry and eruption mechanism. The Minoan activity was preceded by minor eruptions of fine ash. (1) The eruption began with a Plinian phase, from subaerial vent(s) located on the easternmost of the lava shields. (2) Vent(s) grew toward the SW into the flooded depression. Subsequent activity deposited large-scale base surge deposits during vent widening by phreatomagmatic activity. (3) The third eruptive phase was also phreatomagmatic and produced 60% of the volume of the Minoan Tuff. This activity was nearly continuous and formed a large featureless tuff ring with poorly defined bedding. This deposit contains 5–40% lithic fragments that are typical of the westernmost lava shield and appears to have been erupted when caldera collapse began. (4) The last phase consisted of eruption of ignimbrites from vent(s) on the eastern shield, not yet involved in collapse. Collapse continued after eruption of the ignimbrites with foundering of the eastern half of the caldera. Total volume of the collapse was about 19 km3, overlapping the older caldera to form the caldera complex visible today. Intracaldera eruptions have formed the Kameni Islands along linear vents concomitant with vents that may have been sources for the Minoan Tuff.

Description: A new species of a monogenean Isancistrum subulatae (Gyrodactylidae) has been discovered on the arms and tentacles of the cephalopod mollusc Alloteuthis subulata at Plymouth and I. loliginis, on the gills of the same host, has been re-discovered for the first time since its original description in 1912. I. subulatae, like other gyrodactylids, is viviparous, and has been shown by experiments to transfer to new hosts by contagion. In nature such transfers probably take place during copulation of the hosts and since the parasite may occur in numbers of several thousands per host, it may thereby constitute a venereal disease.

Description: During a 10-year study more than 2,000 phytoplankton samples were collected from the entire coast of Peru and analyzed. In general, diatoms were the most abundant group of organisms in all seasons. Predominant species were Rhizosolenia delicatula, Skeletonema costatum Thalassiosira subtilis, Thalassionema nitzschioides and several species of the genus Chaetooeros. Dinoflagellates and flagellates were observed frequently during summer. The mean distribution of the phytoplankton concentration during the 10 years shows the existence of several centers with higher cell densities along the coast, coinciding with the areas of more intense and persistent upwelling. Four major centers have been identified: Pimentel (˜6°S), Chimbote (˜9°S), Callao (˜12°S), and Tambo de Mora-Pisco (˜15°S); and two minor centers, Talara (˜4°S) and Ilo (˜17°S). The relative importance of each center seems to change according to the season. The highest phytoplankton concentration tended to be in the northern part of the coast during fall and winter and in the south through spring and summer.

Description: The growth of the octopus Eledone cirrhosa has been studied in a population from the North Sea off Aberdeen. Data are presented for the growth of individuals isolated in aquarium conditions; the growth of size classes in thefieldpopulation; and preliminary information on the growth relationships of gonad, somatic, cardiac and brain components of the body. At 15 °C Eledone cirrhosa is capable of growing from 10 to 1000 g in 270 days. From octopuses which feed readily in captivity, weight specific growth rates of up to about 3–5 % day-1 for animals of 100 g body weight are recorded, falling to a maximum of about 1–5 % day-1 at body sizes above 500 g. Females stop growing when sexually mature, but in the sample captured they were consistently larger than males, a feature which may account for the 7:1 bias towards the incidence of females. On a wet-weight basis, the mean food incorporation into growth is 37 % of the food ingested, which is 49% of the gross weight of crabs killed. Field data for 1978/79 suggest that animals recruited to the population at the beginning of the year grew steadily until December, overwintered without growing, then grew rapidly for several months in the subsequent year before disappearing from the samples. The estimated average age of those animals and by implication, the life span, is 20 months.

Description: Sedimentation rates (corrected for compaction) from along the passive continental margin of Africa between the Equatorial Fracture Zone and Somalia are used to compare the rates of subsidence of the continental crust since early Mesozoic time. Three distinctive subsidence histories can be identified which correspond with basinal areas that have different structural styles: rifted (west coast), sheared (Equatorial and Agulhas fracture zones) and sunk (zones of vertical tectonics in eastern Africa). A comparison of subsidence rates with other tensional margins (NE USA and the North Sea) and a consideration of the plate tectonic history of the African margins leads to the proposal of a geo and thermodynamic model that takes cognizance of the worldwide mid-Cretaceous rheological discontinuity between taphrogenic and epeirogenic basin formation recognized by Kent, and the more generally accepted, purely plate tectonic driven model of margin subsidence. The new suggestion involves a lower Mesozoic worldwide rise in the geothermal gradient in the lithosphere which produces metamorphism of the base of the continental crust and initiates taphrogenesis along lineaments throughout Gondwanaland. A lowering of the geothermal gradient in the lower Cretaceous produces a switch to epeirogenic subsidence, driven solely by sediment loading and thermal contraction, by Aptian/Albian times. The thermal event facilitated continental separation, and sea floor spreading commenced locally at various times along the active taphrogenic belts. Local thermal and tectonic aberrations associated with this phenomenon over print onto the worldwide pattern of marginal basin subsidence. A further rise in the geothermal gradient may have been responsible for renewed taphrogenesis in eastern Africa in Tertiary times.

Description: We have compiled both laboratory and worldwide field data on electrical conductivity to help understand the physical implications of deep crustal electrical profiles. Regional heat flow was used to assign temperatures to each layer in regional electrical conductivity models; we avoided those data where purely conductive heat flow suggested temperatures more than about 1000°C, substantially higher than solidus temperatures and outside the range of validity of heat flow models. The resulting plots of log conductivity σ versus 1/T demonstrate that even low-conductivity layers (LCL) have conductivities several orders of magnitude higher than dry laboratory samples and that the data can be represented by straight line fits. In addition, technically active regions show systematically higher conductivities than do shield areas. Because volatiles are usually lost in laboratory measurements and their absence is a principal difference between laboratory and field conditions, these materials probably account for the relatively higher conductivities of rocks in situ in the crust; free water in amounts of 0.01–0.1% in fracture porosity could explain crustal conductivities. Other possibilities are graphite, hydrated minerals in rare instances, and sulfur in combination with other volatiles. As most of the temperatures are less than 700°C, partial melting seems likely only in regions of highest heat flow where the conductive temperature profiles are inappropriate. Another result is that at a given temperature, crustal high-conductivity layers (HCL) are more conductive by another order of magnitude and show more scatter than do LCL's. Because the differences between HCL's and LCL's are independent of temperature, we must invoke more than temperature increases as a cause for large conductivity increases; increased fluid concentration in situ seems a probable cause for enhanced conductivities in HCL's. From the point of view of these observations, it does not matter whether the fluids are in communication with the surface or trapped at lithostatic pressures.

Description: The planktonic foraminifer Globigerinoides sacculifer (Brady) was cultured under two different light intensities and in continuous darkness. High light intensity (HLI = 4oo-soo einsteins/m2/s) resulted in a longer lifespan, a greater number of chambers formed, and a larger final shell size compared with individuals cultured under low light intensity (LLI = 20-50 einsteins/m2/s) or in continuous darkness. Shell growth rates were unaffected by increasing light intensity, but gametogenesis was delayed. Continuous darkness induced a rapid onset of gametogenesis in organisms with shell lengths larger than 250 m. Feeding frequency had a greater effect on growth and reproduction than light intensity under conditions of LLI and HLI, but continuous darkness had an overriding effect on growth and reproduction owing to the rapid onset of gametogenesis which terminated the life of the mother cell. Our previous data indicated that the longevity of G. sacculifer was dependent on feeding frequency, and that G. sacculifer cultured under LLI had a lifespan of approximately 2-4 weeks. Present results suggest that the lifespan can vary from a minimum of 8 days for organisms fed daily in continuous darkness to a maximum of 54 days for organisms fed once every 7 days and maintained in HLI. It is concluded that individual G. sacculifer attain a shell size greater than 6oo ,urn only if they maintain their position in the euphotic zone. Prolonged existence below the euphotic zone would result in premature death or gametogenesis following stunted shell growth.

Description: The basement morphology and sediment thickness of the Hess Rise, an oceanic plateau in the central North Pacific, have been mapped on the basis of seismic reflection profiles. The acoustic stratigraphy on and around the rise is correlated with the lithostratigraphy at Deep Sea Drilling Project sites 464, 310, 465, and 466. A total sediment isopach chart of the rise reveals small-scale departures from the expected sedimentary pattern (thick sediment in shallow areas; thin sediment in deep areas). Sediment-filled basement depressions result from mass transport; thin sediment (〈50 m) occurs on steep scarps, basement ridges, and areas affected by bottom currents. A pre-Senonian sediment isopach chart shows a thickening from less than 50 m to more than 250 m of sediment from the northeast to the southwest. This trend seems explainable only in terms of the time-transgressive nature of seafloor formed at a mid-ocean ridge. The axial trend of the rise (N30°W) parallels nearby Mesozoic magnetic lineations and seems to be isochronous as deduced from the Deep Sea Drilling Project data. The Hess Rise began developing in late Aptian time along a segment of the Pacific-Farallon Ridge. Important events in the history of the rise are late-stage volcanism on the southern margin of the rise along the Mendocino Fracture Zone, tectonism and volcanism about 85 Ma that resulted in a major regional unconformity (reflector C), and another period of tectonism and volcanism between 65 and 43 Ma that coincided with the formation of the Emperor Seamounts and created structural benches on the western side of the rise. A significant change in the paleoenvironment that apparently occurred around the Paleogene-Neogene boundary (∼25–20 Ma) caused pronounced changes in the depositional environment and resulted in another major regional unconformity (reflector A).

Description: Five hundred and twenty-eight specimens of Loligo forbesi Steenstrup, from landings in Horta, Faial, Azores, during the year 1 March 1980 to 28 February 1981, were tudied; 59·3 % were males, 40·7 % females. Of the males 80·2 % were sexually mature, of the females 91·6 %, both sexes showing the highest degree of maturity in spring and he lowest in autumn. The mean dorsal mantle length of the mature males was 56·5 cm, or females 33·5 cm. A weight-length relationship was calculated. he stomachs of 622 specimens were sampled, of which 306 contained food. The prey omponents were studied qualitatively. The main prey was fish (82·0%), of which 0·5 % were horse mackerel, Trachurus picturatus, this being the most important food rganism. Preliminary results of statolith readings are given.

Description: The distribution of 234Th, 230Th, and 228Th between dissolved and particulate forms was determined in 17 seawater samples from the Guatemala and Panama basins. Sampling was carried out in situ with battery-powered, submersible pumping systems in which the seawater first passed through a Nuclepore filter (1.0-μm pore size) and then through a cartridge packed with Nitex netting that was impregnated with MnO2 to scavenge the dissolved Th isotopes. Natural 234Th was used as the tracer for monitoring the efficiency of scavenging. For all three isotopes, most of the activity was found in the dissolved form. On the average 4% of the 234Th, 15% of the 228Th, and 17% of the 230Th occurred in the particulate form, though the percentages were found to be strongly dependent on particle concentration. These distributions are not consistent with chemical scavenging models that assume irreversible uptake of Th on particle surfaces. The results can be explained, however, if continuous exchange of Th isotopes between seawater and the particle surfaces is assumed. Vertical profiles of both particulate and dissolved 230Th show increasing concentrations with depth, as required by the assumption of reversible exchange. Some of the dissolved 230Th profiles, however, show a reversal of this trend near the bottom, indicating accelerated scavenging near the water/sediment interface. Kinetics of both adsorption and desorption can be examined if at least two Th isotopes are measured in the same samples. Results show that reaction times are short (a few months) compared to the residence time of suspended matter in the deep ocean (several years), indicating that particles suspended in the deep sea are close to equilibrium with respect to exchange of metals at their surfaces.

Description: Symbiotic luminous bacteria have been described in, and cultured from, a number of species offish and cephalopod. Indeed only in these two groups are extracellular luminous bacteria believed to be utilized as a source of light (see Buchner (1965) and Herring (1978) for references). Despite several earlier investigations of such symbioses in cephalopods the bacteria in these animals have not been adequately identified, nor has the extent of their role been clarified. The ultrastructural relationships between bacteria and the tissues of the squid accessory nidamental gland have been investigated in the non-luminous species Loligo pealei (Lesueur) (Bloodgood, 1977) and Sepia officinalis L. (Van den Branden et al. 1979) but no comparative work on luminous species has been undertaken apart from that on Heteroteuthis dispar (Rüppell), whose photophore does not contain typical luminous bacteria (Dilly & Herring, 1978; cf. Leisman, Cohn & Nealson, 1980). The order Sepioidea contains five families, among which are the two families Sepiolidae and Spirulidae. Though the presence of luminous bacteria is known in some sepiolids (as well as in certain loliginids (order Teuthoidea)) some doubt remains about the source of light in the photophore of Spirula spirula Hoyle. The steady luminescence of this species has prompted speculation that bacteria may be involved (Harvey, 1952). In this paper we compare the anatomy and ultrastructure of the photophores of both Sepiola and Spirula in order to clarify some of these problems.

Description: This is the first detailed analysis of cephalopod beaks from the stomach of a northern bottlenosed whale, Hyperoodon ampullatus (Forster, 1770). The digestive action of many predators barely affects the chitinous beaks of cephalopods and some cetaceans accumulate the beaks in considerable numbers in their stomachs. The present beaks are clean and unbroken. Identification of cephalopod beaks from stomachs of predators such as sperm whales (see Clarke, 1977), seals (Clarke & Trillmich, 1980) and albatrosses (Clarke, Croxall & Prince, 1980) throws considerable light on the biology and relative ecological importance of the species of cephalopods concerned as well as providing useful information on the diet of the predators.

Description: The existence of a southward‐flowing current beneath the northern part of the seasonally reversing Somali Current is documented in a 2½‐year‐long time series of currents obtained at moored stations near 5°N about 30 km off the Somali coast. Its mean annual transport in the layer 150–600 m amounts to about 5×106 m3/s. The undercurrent has a pronounced seasonal cycle in phase with the near surface flow, suggesting a close coupling to the monsoonal wind forcing. With the spin‐up of the deepreaching northern Somali gyre after the onset of the southwest monsoon, the undercurrent is temporarily destroyed in the northern Somali Basin during June/July but is re‐established in August. The undercurrent does not reach 3°N but turns offshore north of that latitude.

Description: The titanium to aluminum ratio in core V19–29 is correlated with aluminosilicate accumulation rates. This correlation may be due to Pleistocene eolian transport fluctuations which alter the mean grain size of sedimented eolian material. The relation between aluminum accumulation rate and Ti/Al, established from accumulation rates integrated over 11,000–50,000 year intervals, can be inverted to compute a high‐resolution record of aluminosilicate and calcium carbonate accumulation rates over the past 130,000 years. Carbonate accumulation rates are closely related to the oxygen isotope record in the core, with a phase lag and damping constant that is compatible with the response time (shown to be only 6000 years) of calcium carbonate in the ocean. Carbonate sedimentation at this site responds to several processes independently correlated with climatic change. The relative importance of these processes for carbonate sedimentation at this site can be constrained by the record in this core and other lines of evidence: 15% of the increased carbonate deposition at this site during glacial periods may be due to diminished NADW (North Atlantic deep water) formation; 10% is due to carbonate productivity decreases in the North Atlantic; 25% may be due to a diminished shallow‐sea carbonate sink; and the residual 50% must be due to a local productivity increase. These assignments are consistent with observations on carbonate paleoceanography in the North Atlantic. Aluminosilicate accumulation rate variations correlate with the record of eolian quartz deposition near northwest Africa and, in a general way, with the climatic record. But in detail the record differs substantially from the oxygen isotope record and may provide independent evidence on the nature of climate dynamics.

Description: Broadband receiver functions developed from teleseismic P waveforms recorded on the midperiod passband of Regional Seismic Test Network station RSCP are inverted for vertical velocity structure beneath the Cumberland Plateau, Tennessee. The detailed broadband receiver functions are obtained by stacking source‐equalized horizontal components of teleseismic P waveforms. The resulting receiver functions are most sensitive to the shear velocity structure near the station. A time domain inversion routine utilizes the radial receiver function to determine this structure assuming a crustal model parameterized by many thin, flat‐lying, homogeneous layers. Lateral changes in structure are identified by examining azimuthal variations in the vertical structure. The results reveal significant rapid lateral changes in the midcrustal structure beneath the station that are interpreted in relation to the origin of the East Continent Gravity High located northeast of RSCP. The results from events arriving from the northeast show a high‐velocity midcrustal layer not present in results from the southeast azimuth. This velocity structure can be shown to support the idea that this feature is part of a Keweenawan rift system. Another interesting feature of the derived velocity models is the indication that the crust‐mantle boundary beneath the Cumberland Plateau is a thick, probably laminated transition zone between the depths of 40 and 55 km, a result consistent with interpretations of early refraction work in the area.

Description: Cephalopod statoliths are paired calcareous stones which lie in cavities, the statocysts, within the skull. They have a form which, though variable, shows promise as a source of criteria for taxonomic and evolutionary studies. As a preliminary to more detailed studies, Clarke (1978) published a description of the form of a generalized teuthoid statolith, coined nomenclature for the various parts and gave a very brief survey of variation of statoliths within the living Cephalopoda. This nomenclature was used in a detailed description of fossilized teuthoid statoliths by Clarke & Fitch (1979). Here, descriptions of the statoliths of the living species Berryteuthis magister (Berry, 1913), Gonatopsis borealis Sasaki, 1923, Gonatopsis (Boreoteuthis) makko Okutani & Nemoto, 1964 and Gonatus fabricii (Lichtenstein, 1818) are given and the fossil Berryteuthis species described in outline by Clarke & Fitch (1979) is compared with B. magister. A statistical analysis of measurements of the statoliths of these five species has been made and the results are presented. This forms the first part of a general description of teuthoid statoliths and similar studies on the Ommastrephidae and the Loliginidae are in preparation.

Description: The eastern boundary of the Caroline plate, in the western equatorial Pacific, is composed of three structural provinces distinguished primarily on the basis of morphology. Each province shows evidence for convergence between the Caroline and Pacific plates though the structural style varies considerably between each province. Most notably, the sense of underthrusting appears to change along the boundary at about 3°N. To the south, at the Mussau System, Caroline lithosphere underthrusts beneath the Mussau Ridge (which is part of the Pacific plate), while to the north the Caroline plate appears to overthrust the Pacific plate. Recently collected seismic reflection profiles across each province documents the structural changes along and across strike of the Caroline-Pacific plate boundary. With this information, we estimate that a minimum of approximately 4 km of crustal shortening has occurred at about 5°N due to convergence of the two plates. Further to the south (about 2°N), simple gravity models suggest that about 10 km of Caroline lithosphere lies beneath the present-day Pacific plate. Using a previously determined pole of rotation describing Caroline-Pacific relative motion (Weissel and Anderson, 1978), we grossly estimate the duration of the convergence between these two plates at about one million years. It is suggested that variation in the convergence rate along the plate boundary provides the primary control on the variation of structural deformation observed between provinces; however, favorable thermal conditions are factors that are considered. If the eastern boundary of the Caroline plate is a region of incipient though perhaps transient subduction, as we postulate, then the geophysical and geological evidence presented can constrain models on the initiation of subduction.

Description: Strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface. This process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone, consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip. Because steady state subduction does not contribute to the deformation at the free surface, deformation observed there is completely equivalent to that produced by the slip cycle alone. The response to that slip is simply the response of a particular earth model to embedded dislocations. For a purely elastic earth model, the deformation cycle consists of a coseismic offset followed by a linear‐in‐time recovery to the initial value during the interval between earthquakes. For an elastic‐viscoelastic earth model (elastic lithosphere over a viscoelastic asthenosphere), the postearthquake recovery is not linear in time. Records of local uplift as a function of time indicate that the long‐term postseismic recovery is approximately linear, suggesting that elastic earth models are adequate to describe the deformation cycle. However, the deformation predicted for a simple elastic half‐space earth model does not reproduce the deformation observed along the subduction zones in Japan at all well if stick slip is restricted to the main thrust zone. As recognized earlier by Shimazaki, Seno, and Kato, the uplift profiles could be explained if stick slip were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km, but independent evidence suggests that stick slip at such depths is unlikely.

Description: Three arrays of ocean bottom seismographs have been deployed to study the seismicity at the northern end of the Juan de Fuca ridge system off western Canada. Nearly 100 events were located with estimated accuracies generally better than ±10 km, all lying on or near the en echalon ridge-transform fault plate boundaries as defined in this area by the magnetic anomalies, the seafloor morphology and by other geophysical data. The depths of 12 events were determined to lie between 2 and 6 km below the top of the crust. The seismograms exhibit clear P and S wave arrivals along with phases that involve P to S and sometimes S to P conversion probably at the base of the sediments beneath the instruments. The event magnitudes have been estimated from signal duration using four calibration events that were well recorded by a land station. The magnitude estimates permit the determination of rough magnitude-frequency of occurrence relations over the magnitude range of 1 to 3 that are in surprisingly good agreement with the recurrence relations for the area at larger magnitudes from 75 years of land station data. The mean P wave velocity in the uppermost mantle from the earthquake data recorded by the sea floor arrays is 7.6 km s-1 and the mean Vp/Vs ratio is 1.71 or a Poisson's ratio of 0.24.