ALBERT

Description: Dissolution rates of small forsterite spheres in superheated melts of basalt, andesite and rhyolite composition have been measured at 1300°C, atmospheric pressure. The rate is constant (83 µm hr−1) in the basalt, regardless of run duration. In the andesite the initial dissolution rate is 200µm hr−1, followed by a decrease to a constant value of 16µmhr−1 in 2–3 hours. Dissolution rate in the rhyolite decreases from an initial value of 1.7 to 〈0.1 µmhr−1 over 280 hours and never reaches a constant rate. Once the rate of dissolution has become constant, the film of contaminated melt that forms in melt about a crystal does not thicken with time, indicating attainment of a steady-state condition. Steady state is attributed to natural convection arising from the difference in density between the film of contaminated melt surrounding a crystal and that beyond. The density difference is approximately 2% of the density of the rock melt.

Description: The deep eastern Arctic basin between the Lomonosov Ridge and the Eurasian continental margin differs from other ocean basins in the very slow spreading of its floor and unusual depositional environment under perennial sea-ice cover. The recent expedition ARK IV/3 of RV Polar stern for the first time made geoscientific investigations from the northern margin of the Barents Sea north to the Nansen-Gakkel Ridge. Much deeper than most other mid-ocean ridges, this ridge is poorly-surveyed, but has a central valley which in places is deeper than 5.5 km, 1–1.5 km below the basin floors on either side. Heat flow in the central part of the valley is very rapid; both basement rocks and overlying sediments showed unexpectedly the influence of intense and long-term hydrothermal activity. The sediments on the northern and southern flanks of the ridge are slightly calcareous pelagic mud layers alternating with carbonate-free horizons, where up to 40% of the sedimentary section is soft mud clasts. Similar mud aggregates were observed on the surface of the multi-year sea ice, appearing to represent a special type of sediment transport by sea ice in the Transpolar Drift. In contrast to the western Arctic, Fram Strait and the Norwegian-Greenland Sea, gravel is rarely found in sediment cores. Recovered cores indicate that icebergs and sea ice carrying coarse sediment seldom rafted detritus to the study area during the last approximately 300,000 years.

Description: This article describes the natural history of a large colony of emperor penguins Aptenodytes for steri , its size, dispersal pattern of chicks, and associations with other bird and mammal species. A mid-season count of 19,364 chicks indicated that about 20–25,000 breeding pairs had been present in June and July. The colony was fragmented into several sub-groups which showed different mean sizes of chicks and survival to fledging. Other species observed included leopard seals Hydrurga leptonyx , the only major predators, which preyed heavily on both adults and fledging chicks. Fledgelings left the colony over a period of about 10 days; departure was an active process in which the chicks walked to the ice edge and dispersed in groups, swimming consistently southward. At this time they were still in about 60% down and weighed about 10 kg, having lost some 30% of the heaviest mass achieved during parental feeding.

Description: Within the Western Ross Sea, there are six emperor penguin colonies of widely different size that occur exclusively on sea ice. In 1990 a survey of all six sites, two by close overflights and four from the ground, showed that the breeding habitats were highly variable. The most important physical characteristics of these habitats appear to be stable fast ice, nearby open water, access to fresh snow, and shelter from the wind.

Description: Light absorbed by the photoreceptor membranes of the retina is transformed by a series of biochemical steps into changes in receptor potential. The visual pigment, rhodopsin, and associated enzymes which relay the visual signal belong to a widespread family of receptorenzyme complexes which transmit sensory, hormonal and neurotransmitter signals into cells. In the invertebrate visual system, rhodopsin activates enzymes which increase cytoplasmic calcium. The highly specialised and structurally ordered photoreceptors of the squid retina provide a favourable system for studying the mechanisms of these enzyme pathways.

Description: Arm autotomy was induced in a living specimen of Metacrinus rotundus (Echinodermata: Crinoidea). An arm was autotomized at a ligamentary articulation known as a cryptosyzygy, following incision by scissors distal to the break point. Although sessile stalked crinoids cannot entirely escape from a predatory attack by arm autotomy and they do not have an active defense, arm autotomy at cryptosyzygies reduces damage and arm loss by effective distribution, and by minimizing trauma and facilitating subsequent regeneration. The paradigmatic distribution of cryptosyzygies in which arm loss is set at a minimum, compared with the actual distribution, shows that these two patterns are similar and that actual specimens successfully reduce arm loss by the effective distribution of cryptosyzygies. The crinoid branching pattern also affects arm loss, and two different paradigms are discussed: anti-predatory and harvesting. Arm branching patterns of various isocrinids have tended toward the anti-predatory configuration from the Jurassic to the Recent, suggesting that the isocrinids have coped with increased predation. Shallow-water comatulids generally adopt the anti-predatory paradigm in their branching pattern, whereas many deep-water, stalked crinoids adopt a harvesting paradigm, reflecting that shallow-water comatulids receive more predatory attacks than do deep-water crinoids.

Description: The functional morphology of the buccal mass of 23 species of cephalopod (Octopoda, 4 species; Teuthoidea, 17; Sepioidea, 2) was investigated by gross dissection, histology and observations on fresh preparations. Cephalopod beaks lack a joint or articulation point. The jaws slide and rotate around an area rather than a fixed point. During closing the superior mandibular muscle (SMM) provides the force of a bite and the largest movement vector, whilst the inferior mandibular muscle (IMM) acts to retract the upper beak, causing shearing action. Dorsal portions of the lateral mandibular muscles (LMM) flex the upper beak walls outwards, probably to accomodate the backwards sweep of the radula and buccal palps during closing. To open the beaks, the ventral portions to the lateral mandibular muscles pull the rear lateral walls of the two beaks towards each other, moving the lower beak back relative to the upper. The buccal mass weighs more in decapods (0.65-4.34% of body weight) than octopods (0.49-0.77%). The weight difference is mainly accounted for by the size of the superior mandibular muscle. Beak shape and muscle volume are related. Increasing the size of the upper beak hood and lateral wall area results in larger SMM and LMM respectively Increasing hood size in the lower beak increases IMM size, and altering the angle by which the wings meet the lateral wall changes the volume of the SMM and LMM. To accomodate the decapod pointed upper rostrum, the lateral walls of the lower beak have shortened in length, whilst increasing in breadth and surface relief to maintain the area available for muscle insertion. In species with a lateral wall ridge or fold (e.g. Onychoteuthis) this may mark the insertion point of the LMM.

Description: The influence of photoperiodicity on hatching of Loligo forbesi and Loligo vulgaris embryos was investigated under different experimental light-dark (LD) conditions. The transition from light to dark stimulated hatching and functions as a "Zeitgeber" or synchronizer. Independent of the timing and duration of the dark period most embryos hatched soon after termination of the light period. Embyros which had developed in constant light, showed no hatching rhythm at all. If these embryos were exposed to a dark shock most embryos hatched soon after the onset of darkness. A twilight shock, in which the light was reduced by 50% (i.e. 50 µE s -1m-²), could not simulate hatching. Embryos which were kept from stage X on in an artifically controlled LD cycle, preferentially hatch in a period which coincides with the period at which darkness usually occured when placed in constant illumination from stage XX onwards.

Description: A correlation of the Campanian–Maastrichtian boundary is attempted using foraminiferal and nannoplankton data from two areas: the eastern North Atlantic and northwestern Germany. The Boreal benthic and Tethyan planktonic foraminiferal zonation schemes are applied to Site 548A, where both foraminiferal groups occur frequently. A direct comparison of both biozonations reveals that the base of the Maastrichtian, according to planktonic foraminifers, has to be placed in the Upper Campanian of the Boreal benthic foraminiferal biozonation, which concurs with the nannoplankton results. The Tethyan Middle and Upper Maastrichtian are probably equivalent to the Upper Maastrichtian in the Boreal sense. The bases of the Maastrichtian substages are thus diachronous between the Boreal and Tethyan realms. Palaeotemperatures (which were estimated using the oxygen isotopic composition of the Goban Spur chalks) indicate, in combination with palaeowind directions, that the faunal and floral distribution pattern recorded is the result of a stable, warm water outflow from the northwest European epicontinental seas through the Channel area to the Celtic Shelf sea and Goban Spur. This mechanism appears to have been a dominant separating factor of the Boreal and Tethyan bioprovinces on the western European Shelf.

Description: The groundmass of andesitic dykes at Sezaki, southwest Japan, has trachytic texture and contains microscopic shear zones. The shear zones comprise a conjugate pair formed by flattening of the solidifying dyke rock, probably caused by the magma pressure of the still molten part of the dyke. This pressure shortened the solidifying rock perpendicular to the dyke margins and caused it to extrude parallel to the magma flow direction. The groundmass shears indicate that locally the magma flowed 60° upward in the dykes. It is concluded that while groundmass shears are a useful indicator of flow direction in dykes, phenocryst alignment in dykes is strongly influenced by magma-pressure flattening and thus may be a poor indicator of flow direction.

Description: Outer membrane (OM), cytoplasmic membrane (CM) and intracytoplasmic membranes (ICM) from the halophilic phototrophic purple sulphur bacterium Ectothiorhodospira mobilis 9903 were purified and characterized. The three membrane fractions were significantly different in regard to protein profiles on SDS-PAGE, and to the composition of amino acids, fatty acids and lipids. The presence of lipoproteins, the occurrence of lyso-phosphatidyl-ethanolamine and an increased content of saturated and short-chain fatty acids are characteristic properties of the OM. CM and ICM fractions are different on the basis of buoyant density, of protein profiles and amino acid composition, and due to the presence of succinate dehydrogenase activity in CM. In addition, CM and ICM showed significant differences in pigment content and absorption spectra.

Description: The upper bathyal sea-pen Kophobelemnon stelliferum extends to depths of about 1600 m in the Porcupine Seabight, to the south-west of Ireland, but is rare below about 1150 m. Photographic data suggest that the species attains numerical abundances of more than 2 m−2and a wet weight biomass of at least 4 g m−2. The highest densities, however, do not necessarily correspond to the highest biomass values since there is a clear depth-related change in population structure. The largest sea-pens are restricted to the deeper parts of the bathymetric range of the species. There is also a marked change in the growth form at a total colony length of about 250 mm, with larger colonies having relatively more polyps than smaller ones. The sexes are separate in Kophobelemnon stelliferum and the sex ratio of colonies is about 1:1. The maximum oocyte diameter is about 800 μm, but there is no evidence of seasonal reproduction by this pennatulid in the Porcupine Seabight.

Description: The free-running locomotor activity rhythms of freshly-captured swimming crabs Liocarcinus holsatus and L. depurator have been studied in constant conditions in the laboratory. L. holsatus captured in the intertidal zone of sandy beaches showed strong circatidal activity rhythms with maximum activity at high tide. L. holsatus captured in the sublittoral zone had a clear tendency to show circadian activity rhythms with highest activity during day-time hours. L. depurator occurred only sublittorally and showed circadian activity patterns with highest activity during the night. Exposure to hydrostatic pressure cycles of tidal amplitude and periodicity, entrained strong circatidal activity rhythms in previously arhythmic L. holsatus. This activity pattern also showed a marked circadian component. Exposure to the same regime entrained a circadian rhythm, but not a circatidal rhythm in L. depurator. In the sublittoral zone L. depurator is active mainly during the night, whereas L. holsatus, is active mainly during the day. This may constitute a behavioural mechanism for minimizing competitive interactions between these two sympatric crabs

Description: Serological methods for prey identification have been applied to detection of residues ofsandeel (Ammodytidae) protein in faeces of common seals (Phoca vitulina) and grey seals(Halichoerus grypus) from the Moray Firth, north-east Scotland. Antisera raised to muscleprotein from Ammodytes marinus were evaluated by testing their reactions with proteinextracts made from a range of North Sea fish species and protein residues in in vitro digestates,seal digestive tracts and seal faeces. It was concluded that, using fused rocketimmuno-electrophoresis, linkage of precipitin peaks from unknown samples with peaksfrom standard sandeel extract was a reliable indicator of the presence of sandeel in theunknown sample. Seasonal variation in the incidence of sandeels in common seal diet in theMoray Firth was examined by identifying otoliths, bones, and proteins, and all threemethods indicated that sandeels occurred in the majority of samples tested in the summer,but were less important during the winter. Proteins were detected in fewer samples thanotoliths, particularly in February and March. Possible reasons for this difference arediscussed. Serological identification of sandeel proteins is potentially applicable to dietarystudies on all marine predators.

Description: Age and growth were estimated in the European squid, Loligo vulgaris, by examining growth increments in the statoliths of 203 specimens collected from off the French Mediterranean coast. Length and increment data were analyzed assuming that the increments were formed daily. The relationships between age and length showed that: growth rate varied considerably among individuals; growth was double exponential; the squids grew on average to 240 mm ML at 240 d from hatching, with a maximum of 350 mm at 240 d; the life span is probably about one year.

Description: Some of the limits to the use of serology to identify prey species in the digestive tracts of cephalopods have been evaluated. Cuttlefish, Sepia officinalis, were given meals of krill slurry (Euphausia superba). Protein extracts of contents from four regions of the digestive tract, stomach, caecum, digestive gland and intestine, were tested for prey antigenicity. Digestion times (loss of antigenicity) ranged from 1 to 8 h depending on sampling site. Stomach and caecum emptied rapidly, but meal antigenicity persisted longer in the digestive gland. The Sepia experiments provide a basis for interpretation of results from natural predation by cephalopods).

Description: The stomachsof 23 striped dolphins (Stenella coeruleoalba Meyen, 1833, Cetacea), stranded along the Ligurian coast (western Mediterranean Sea), contained 32 species of cephalopods, crustaceans and fishes, totalling an estimated 2,723 prey specimens representing about 36 kg in weight. Cephalopods and bony fishes were equally important in the diet (50%). Todarodes sagittatus (34.5%) and Micromesistius poutassou (25.9%) were found to be the most important food species. Other species belonging to six cephalopod families, three crustacean families and nine bony fish families, contributed to the diet with variable numbers, weights, and occurrences, demonstrating the opportunistic character of striped dolphin feeding.

Description: Thirty-four adult individuals of Loligo forbesi (males and females with dorsal mantle lengths from 27–77 cm) were observed in captivity in a 3 m diameter closed sea-water system on Faial Island, Azores. Squids were caught by jigging and were fed with horse mackerel (Trachurus picturatus) and chub mackerel (Scomber japonicus), either alive or dead. The maximum survival was 73 days. Feeding behaviour was dependent upon both the size of prey and its state of preservation;e.g. the squid would eat the head of small fish (〈 about 15 cm), reject the head of medium-sized fish (about 15–35 cm) and would eat only the dorsal part of a big fish (〉 about 35 cm) or a fish poorly preserved. Seventeen chromatic, 9 postural and 6 movement components of body patterns were observed and described. Conspecific interactions considered to be aggression and dominance were observed among males; no such interactions occurred when one male and two females were kept together. Body patterns in relation to relaxation, stress, shock, feeding, locomotion and aggression are also described.

Description: The presence of Stoloteuthis leucoptera in the Mediterranean is recorded on the basis of three specimens, including an adult male, caught by IKMT and by commercial otter-trawl in the Ligurian Sea. The hypothesis of a recent immigration is discussed. The list of Mediterranean cephalopods (Mangold Wirz, 1963; Torchio, 1968; Bello, 1986; Mangold & Boletzsky, 1987) includes the Sepiolidae of the subfamily Heteroteuthinae, whose members are supposed to be pelagic throughout their life cycle. Mangold Wirz (1963) recognizes in the Mediterranean fauna the unique species Heteroteuthis dispar, the other authors include H. atlantis Voss, which Voss himself (1955) reported at Messina. To this group may now be added Stoloteuthis leucoptera (Verrill, 1878) a species until now recorded in limited Atlantic areas. Verrill (1881) wrote “This species is an exceedingly beautiful one, when living, owing to the elegance and brilliancy of its colours and the gracefulness of its movements. In swimming it moves its fins in a manner analogous to the motion of the wings of a butterfly.”

Description: Samples of two loliginid squids Alloteuthis africana and A. subulata were collected from the continental shelf off the west Sahara in August-September 1987. Statoliths were taken from 124 specimens and processed using statolith ageing techniques. Statoliths of both species were very similar in shape. In the ground statolith, growth increments were examined and grouped into four growth zones distinguished mainly by the width of the increments. Age of adult mature males of both species did not exceed eight months, that of females six months. Alloteuthis africana grew faster than A. subulata in weight and, particularly, in length. At age 180 d the mantle of A. africana was twice as long and the body weight 1·2–1·5 times as large. Both species matured over a wide range of sizes and ages (from 120 to 180 d). The life span of A. africana and A. subulata hatching between January and May on the west Saharan shelf is about six months, much shorter than that of A. subulata in its northern temperate range.

Description: Samples of female lllex argentinus were taken from the catch of a Japanese squid jigging vessel on the Patagonian Shelf during March 1986. Morphometrics of the somatic and reproductive organ systems and the histological structure of the mantle in relation to maturation were examined. The data suggest that growth and maturation occur simultaneously during most of the time that lllex argentinus females are on the feeding grounds. In a squid of a ‘standard’ mantle length the whole body mass increases relative to mantle length during maturation and growth of the reproductive organs. This is accompanied by a small but significant decrease in the relative mass of the mantle, head and viscera whilst the mass of the digestive gland remains constant. Although mantle mass of a ‘standard’ female squid decreases relative to mantle length with maturity this is not associated with degeneration of the mantle muscles. Energy and nutrient resources for maturation are apparently derived from the squid's food, not from reserves, and during the course of maturation there is an increasing shift of emphasis from somatic growth to production of gonad and accessory reproductive organs.

Description: The timing of spawning and recruitment in the squid Loligo forbesi in Scottish waters is described on the basis of data from three sources: monthly samples of squid caught by commercial trawls (1986–1988), egg masses found by fishermen (1987–1991), and statistical data on animals caught by research trawls (1978–1987). Spawning females were present in samples from December to June, with peak spawning occurring in March. Most records of egg masses were from these months, but eggs were also found in August and September. These results suggest that there is an extended spawning season. Small squid (≤100 mm dorsal mantle length) were rarely present in commercial samples, but were recorded in research samples almost all year round. Thus there appears to be more or less continuous recruitment into the catchable population. The results of the present study are consistent with published data from other parts of the geographic range in that there is a regular seasonal peak in spawning, and spawning adults disappear from the population in summer. Further interpretation of the life-cycle of this species is not justified on the basis of current knowledge, and more information is needed on migrations, geographical variation, and lifespan in Loligo forbesi.

Description: Cephalopod remains from the stomachs of a Risso's dolphin (Grampus griseus Cuvier, 1812, Cetacea) entangled in a fishing net off the Ligurian coast (central Mediterranean Sea) include squids Ancistroteuthis lichtensteini, Histioteuthis bonnellii, H. reversa and Todarodes sagittatus and the sepiolid Heteroteuthis dispar. All these cephalopods live in oceanic water including water over the steep continental slope where Risso's dolphin is frequently sighted. Histioteuthis reversa contributed 78% of the cephalopods by number, 81% of the wet weight and 73% of the dry weight and calorific value. The total calorific value of the cephalopods represented by lower beaks was 17,300 kj.

Description: The stomach contents of 235 specimens of the squid Sthenoteuthis oualaniensis (4·3–36·5 cm mantle length, ML) were examined. A detailed list of 60 species of prey, comprising young and adult squid, is given together with their frequency of occurrence and proportional contribution. The size and number of each food item was investigated. Three ontogenetic size-groups of S. oualaniensis were distinguished: I, fry and young (4–10 cm ML), micronektonic epipelagic plankton-eaters; II, transient critical size group (10–15 cm ML), converting from feeding on planktonic crustaceans and fish larvae to myctophid fishes; III, medium-sized (adult) nyctoepipelagic nektonic predators (15–36·5 cm ML), feeding primarily on myctophids and secondarily on squid. Myctophids (genera Symbolophorus, Myctophum and Hygophum) were the most abundant prey in the diet of adult S. oualaniensis from different parts of its distribution.

Description: Samples of male Illex argentinus were taken from the catch of a Japanese squid jigging vessel on the Patagonian Shelf during March 1986 and an analysis was carried out on the morphometrics of the somatic and reproductive organ systems in relation to maturation. The data show that growth and maturation occurred simultaneously during most of the time that Illex argentinus males were on the feeding grounds over the southern Patagonian Shelf. In a squid of a ‘standard’ mantle length the whole body mass increased relative to mantle length during maturation and this could be attributed to the increase in mass of the reproductive and accessory reproductive organs. During maturation the mantle and digestive gland mass showed no significant change relative to mantle length. The mass of the head increased and the mass of the viscera decreased relative to mantle length. In male Illex argentinus, as in the female, the energy and nutrient resources for maturation are derived from the squid's food and during the course of maturation there is an increasing shift of emphasis from somatic growth to production of gonad and accessory reproductive organs. The proportional investment of body mass in reproductive and accessory reproductive organs predicted for a fully mature male Illex argentinus was less than half that of the female.

Description: During a study based on catches taken in the northern North Sea by selected Scottish fishing boats during 1985–1992, large numbers of the normally rare short-fin squid, Todaropsis eblanae (Cephalopoda: Ommastrephidae), were recorded in 1987 and 1990. Our findings, supported by data obtained from plankton/young fish surveys in 1988 and 1989, suggest that in northern waters Todaropsis eblanae generally mates and spawns during late summer and early autumn (June-November). Successful hatching events appear to occur during October-March, producing juvenile (stage I) squid in the early part of the year (January-June). Estimations of maximum male reproductive output and female fecundity were up to 130 spermatophores and ~28,000 eggs per individual, respectively.

Description: Statoliths of Loligo gahi were sampled in the fishery region 45–47°S on the Patagonian shelf during September 1989. Peculiarities of the growth zones in the ground statoliths of adults are described. Maximum age of large maturing and mature females (130–160 mm of mantle length, ML) was estimated to be 325–345 d, that of large mature males (250–290 mm ML) ranged from 360 to 396 d. The squid Loligo gahi d'Orbigny, 1835, occurs in temperate shelf and upper slope waters of the Atlantic and Pacific coasts of South America and is caught commercially by the international fleet in the southern part of the Patagonian shelf within the Falkland Islands Interim Conservation Zone (FICZ) (Roper et al., 1984; Csirke, 1987). Occasionally, dense shoals of L. gahi appear in the fishery region 45–47°S off the Exclusive Economic Zone of Argentina (EEZA) and have been caught in significant numbers by trawlers at depths of 120–150 m in September-October (Chesheva, 1990). Loligo gahi is a medium sized loliginid; in Falkland waters males attain 350 mm ML, females 210 mm ML (Hatfield, 1991), while in the fishery region 45–47°S maximum size is 260 mm and 160 mm, respectively (Chesheva, 1990). Patterson (1988) revealed two Falkland spawning stocks of L. gahi of unclear status, spring-spawners and autumn-spawners (austral seasons) and pointed out that the life span of squid of each stock lasted ~1 y. Recently Hatfield (1991) used statoliths to elucidate Patterson's (1988) estimations of age and growth of Falkland stocks of L. gahi and confirmed the 1-y duration of L. gahi's life span.

Description: Organic-rich shales sampled from the aples Beach section of the Monterey Formation. Califomia. contain authigenic phosphorite phases which apparently formed within bacterial mat laminations. Light and scanning electron microscope observations show that the fossilized remains ofthese mats are similar to communities of filamentous sulfur-oxidizing bacteria found today at slope-depth, sediment, oxic anoxic interfaces. The crystal size and habits ofthe phosphatic minerals resemble contemporaf) prec1pitates in contact with pore water solutions. Mineralogical and chemical analyses ofthe most phosphatic layers show that some are a nearly pure carbonate fluorapatite (or francolite). These la)ers are lightly colored and are sandwiched between black siliceous muds with 〈0.2% CaCOJ . and organic carbon contents that excecd 25%. In othcr phosphatic intcrvals of thc Naplcs Beach section. ca leite is a major diluent oflight and dark layers. The C:P ratio of a single modern bacterial mat sample shows that these benthic communities are more enriched in phosphorus than planktonic organic matter. Thus, the generally believed premise that authigenic phosphorite formation results from organic matter diagenesis in near-surface anoxic sediments is hcre modified by the contention that such transformations are more highly favored in sediments supporting massive microbial communities.

Description: The data presented provides new information on the distribution of Antarctic squids and on the summer diet of the emperor penguins. The diet of 58 adult emperor penguins (Aptenodytes forsteri) on the fast ice of the Drescher Inlet, Vestkapp Ice Shelf (72°52′S, 19°25′W) in the eastern Weddell Sea was investigated. Prey consisted principally of squid, fish, krill, amphipods and isopods. Squids were identified by the lower beaks and allometric equations were used to estimate the squid biomass represented. Beaks occurred in 93% of the stomach samples. Each sample contained a mean of 27 beaks (range 1–206). Ninety-two percent of the squids could be identified by the lower beaks and belonged to four families (Onychoteuthidae, Psychroteuthidae, Neoteuthidae and Gonatidae). The most abundant squid was Psychroteuthis glacialis which occurred in 52 samples with lower rostral lengths (LRL) ranging from 1.4–7.2 mm. Forty-five samples contained Alluroteuthis antarcticus (LRL range 1.8–5.8 mm), 17 Kondakovia longimana (LRL range 4–12.1 mm), and four Gonatus antarcticus (LRL range 4.1–6.1 mm). In terms of biomass K. longimana was the most important species taken by the penguins comprising 50% of total estimated squid wet mass (245348 g) in 1990 and 48% in 1992 (154873 g). However, if only fresh beaks were considered for estimations of squid consumption, i.e. beaks that have been accumulated for not longer than 5–6 days in the stomachs, squid diet was of minor importance. Then total squid wet mass accounted for only 4809 g in 1990 and 5445 g in 1992 which implies that one penguin took c.30 g squid d−1 with P. glacialis and A. antarcticus being the most important by mass. The prey composition suggests that emperor penguins take squid at the steep slope regions of the eastern Weddell Sea.

Description: We investigate the weakly nonlinear spatial evolution of helical disturbances of an axisymmetrical jet which are the analogue of three-dimensional disturbances, such as a single oblique wave (the wave vector is directed at an angle to the main flow velocity) in plane-parallel flows. It is shown that when a supercriticality is large enough, the perturbation amplitude A grows in the streamwise direction (along z) explosively: A ~ (z0—z)-5/2, though more slowly than in the case of essentially three-dimensional disturbances in the form of a pair of oblique waves (A ~ (z0 — z)-3; Goldstein & Choi 1989). The nonlinearity needed for such a growth, is due equally to the cylindricity of shear layer and to the spatial character of the evolution (in the temporal problem the ‘evolution’ contribution is absent). At a smaller supercriticality, the evolution equation has a non-local (integral in z) nonlinearity, unusual for the regime of a viscous critical layer. Scenarios of disturbance development for different levels of supercriticality are studied, with proper account taken of viscous broadening of the flow. © 1994, Cambridge University Press. All rights reserved.

Description: In an earlier paper (Davey 1978) the first author investigated the linear stability of flow in a straight pipe whose cross-section was an ellipse, of small ellipticity e, by regarding the flow as a perturbation of Poiseuille flow in a circular pipe. That paper contained some serious errors which we correct herein. We show analytically that for the most important mode n = 1, for which the circular problem has a double eigenvalue c0 as the ‘swirl’ can be in either direction, the ellipticity splits the double eigenvalue into two separate eigenvalues c0±e2c12, to leading order, when the cross-sectional area of the pipe is kept fixed. The imaginary part of c12 is non-zero and so the ellipticity always makes the flow less stable. This specific problem is generic to a much wider class of fluid dynamical problems which are made less stable when the symmetry group of the dynamical system is reduced from S1 to Z2. In the Appendix, P. G. Drazin describes simply the qualitative structure of this problem, and other problems with the same symmetries, without technical detail. © 1994, Cambridge University Press. All rights reserved.

Description: This paper describes a combined computational and experimental study of the flow between contra-rotating disks for — 1 ≤Γ≤0 and Reϕ= 105, where is the ratio of the speed of the slower disk to that of the faster one and Reϕ is the rotational Reynolds number of the faster disk. For Γ = 0, the rotor-stator case, laminar and turbulent computations and experimental measurements show that laminar Batchelor-type flow occurs: there is radial outflow in a boundary layer on the rotating disk, inflow on the stationary disk and a rotating core of fluid between. For Γ= — 1, the laminar computations produce Batchelor-type flow: there is radial outflow on both disks and inflow in a free shear layer in the mid-plane, on either side of which is a rotating core of fluid. The turbulent computations and the velocity measurements for Γ = — 1 show Stewartson-type flow: radial outflow occurs in laminar boundary layers on the disks and inflow occurs in a non-rotating turbulent core between the boundary layers. For intermediate values of Γ, transition from Batchelor-type flow to Stewartson-type flow is associated with a two-cell structure, the two-cells being separated by a streamline that stagnates on the slower disk; Batchelor-type flow occurs radially outward of the stagnation point and Stewartson-type flow radially inward. The turbulent computations are mainly in good agreement with the measured velocities for Γ = 0 and Γ= — 1, where either Batchelor-type flow or Stewartson-type flow occurs; there is less good agreement at intermediate values of Γ, particularly for F = —0.4 where the double transition of Batchelor-type flow to Stewartson-type flow and laminar to turbulent flow occurs in the two-cell structure. © 1994, Cambridge University Press. All rights reserved.

Description: Based on linear potential theory, the general three-dimensional problem of steady supersonic flow inside quasi-cylindrical ducts is formulated as an initial-boundary-value problem for the wave equation, whose general solution arises as an infinite double series of the Fourier-Bessel type. For a broad class of solutions including the general axisymmetric case, it is shown that the presence of a discontinuity in wall slope leads to a periodic singularity pattern associated with non-uniform convergence of the corresponding series solutions, which thus are unsuitable for direct numerical computation. This practical difficulty is overcome by extending a classical analytical method, viz. Kummer's series transformation. A variety of elementary flow fields is presented, whose complex cellular structure can be qualitatively explained by asymptotic laws governing the propagation of small perturbations on characteristic surfaces. © 1994, Cambridge University Press. All rights reserved.

Description: This paper determines the ray structure of a spinning acoustic mode propagating inside a semi-infinite circular cylindrical duct, and thereby determines the ray structure of the field radiated from the end of the duct. Inside the duct, but outside of a caustic cylindrical surface, the rays are piecewise linear helices; on striking the rim of the end-face of the duct, these rays produce ‘Keller cones’ of diffracted rays. The cones determine the structure of the radiated field: for example, no rays penetrate two cone-shaped far-field quiet zones centred on the duct axis; two rays pass through each point in a forward loud zone; and one ray passes through each point in a rearward loud zone. The two rays through each point in the forward loud zone interfere to produce an oscillatory directivity pattern. One quarter of the rays on each cone point back inside the duct and produce the reflected field. Thus the rim of the end-face of the duct acts as a ‘ring source’, in which the radiated and reflected fields have their origin. Every propagating duct mode determines a polar angle and an azimuthal angle; these are taken as parameters specifying the mode and are used to calculate the positions and angles of all the rays. The mathematical method on which the paper is based is Debye's approximation for the Bessel function which appears in the expression for the duct modes; the approximation shows also that the duct contains a region of smooth helical rays on which the field consists of inhomogeneous waves: this region is the inner cylinder, lying inside the annulus of piecewise linear helical rays. The results of the paper are very promising for the application of Keller's geometrical theory of diffraction to detailed calculations of the sound radiated from aeroengine ducts. An alternative description of the field, using Cargill's meridional rays, is summarized.

Description: The effects of thermal conditions on the patterns of two-dimensional Boussinesq convection are studied by numerical integration. The adopted thermal conditions are (i) the heat fluxes through both upper and lower boundaries are fixed, (ii) the same as (i) but with internal cooling, (iii) the temperature on the lower boundary and the heat flux through the upper boundary are fixed, (iv) the same as (iii) but with internal cooling, and (v) the temperatures on both upper and lower boundaries are fixed. The numerical integrations are performed with Ra = 104 and Pr = 1 over the region whose horizontal and vertical lengths are 8 and 1, respectively. The results confirm that convective cells with the larger horizontal sizes tend to form under the conditions where the temperature is not fixed on any boundaries. Regardless of the existence of internal cooling, one pair of cells spreading all over the region forms in the equilibrium states. On the other hand, three pairs of cells form and remain when the temperature on at least one boundary is fixed. The formation of single pairs of cells appearing under the fixed heat flux conditions shows different features with and without internal cooling. The difference emerges as the appearance of a phase change, whose existence can be suggested by the weak nonlinear equation derived by Chapman & Proctor (1980). © 1994, Cambridge University Press. All rights reserved.

Description: Gravity wave radiation by vortical flows in the /-plane shallow-water equations is investigated by direct nonlinear numerical simulation. The flows considered are initially parallel flows, consisting of a single strip in which the potential vorticity differs from the background value. The flows are unstable to the barotropic instability mechanism, and roll up into a train of vortices. During the subsequent evolution of the vortex train, gravity waves are radiated. In the limit of small Froude number, the gravity wave radiation is compared with that predicted by an appropriately modified version of the Lighthill theory of aerodynamic sound generation. It is found that the gravity wave field agrees well with that predicted by the theory, provided typical lengthscales of vortical motions are well within one deformation radius. It is found that the nutation time for vortices in the train increases rapidly with increasing Froude number in cases where the potential vorticity in the vortices is of the same sign as the background value, whereas the nutation time is almost independent of Froude number in cases where the potential vorticity in the vortices is zero or of opposite sign to the background. Consequently, in the former cases, the unsteadiness of the flow decreases with increasing Froude number, so the effect of the inertial cut-off frequency is increased, leading to an optimal Froude number for gravity wave radiation, above which the intensity of the radiated waves decreases as the Froude number is further increased. It is proposed that the existence of a finite range of interaction within the vortices, for flows with positive vortex potential vorticity, may account for the strong dependence of nutation time on Froude number in those cases. The interaction scale within the vortices becomes infinite in the limit of zero vortex potential vorticity, and so the arguments do not apply in those cases. © 1994, Cambridge University Press. All rights reserved.

Description: Oscillations of a tank at a near-resonant frequency have been shown to produce a response which changes from a ‘hard-spring’ to a ‘soft-spring’ response as the depth passes through a critical value. This paper investigates the transition region and it is shown, using a symbolic manipulator, that in fact the large-amplitude response is that of a soft spring on either side of this critical depth. © 1994, Cambridge University Press. All rights reserved.

Description: Premixed H2/02/N2 flames propagating in two-dimensional turbulence have been studied using direct numerical simulations (DNS: simulations in which all fluid and thermochemical scales are fully resolved). Simulations include realistic chemical kinetics and molecular transport over a range of equivalence ratios ©〉 {& — 0.35, 0.5, 0.7, 1.0, 1.3). The validity of the flamelet assumption for premixed turbulent flames is checked by comparing DNS data and results obtained for steady strained premixed flames with the same chemistry (flamelet ‘library’). This comparison shows that flamelet libraries overestimate the influence of stretch on flame structure. Results are also compared with earlier zero-chemistry (flame sheet) and one-step chemistry simulations. Consistent with the simpler models, the turbulent flame with realistic chemistry aligns preferentially with extensive strain rates in the tangent plane and flame curvature probability density functions are close to symmetric with near-zero means. For very lean flames it is also found that the local flame structure correlates with curvature as predicted by DNS based on simple chemistry. However, for richer flames, by contrast to simple-chemistry results with non-unity Lewis numbers (ratio of thermal to species diffusivity), local flame structure does not correlate with curvature but rather with tangential strain rate. Turbulent straining results in substantial thinning of the flame relative to the steady unstrained laminar case. Heat-release and H202contours remain thin and connected (‘flamelet-like’) while species including H-atom and OH are more diffuse. Peak OH concentration occurs well behind the peak heat-release zone when the flame temperature is high (of the order of 2800 K). For cooler and leaner flames (about 1600 K and for an equivalence ratio below 0.5) the OH radical is concentrated near the reaction zone and the maximum OH level provides an estimate of the local flamelet speed as assumed by Becker et al. (1990). © 1994, Cambridge University Press. All rights reserved.

Description: The modification of the mean and fluctuating characteristics of a flat-plate boundary layer subjected to nearly isotropic free stream turbulence (FST) is studied experimentally using hot-wire anemometry. The study is focussed on the region upstream of the transition onset, where the fluctuations inside the boundary layer are dominated by elongated flow structures which grow downstream both in amplitude and length. Their downstream development and scaling are investigated and the results are compared with those obtained by previous authors. This allows some conclusions about the parameters which are relevant for the modelling of the transition process. The mechanisms underlying the transition process and the relative importance of the Tollmien–Schlichting wave instability in this flow are treated in an accompanying paper (part 2 of the present report). © 1994, Cambridge University Press. All rights reserved.

Description: Linear birefringence measurements of dilute and semi-dilute polyisobutylene solutions following flow through a disordered fixed fibre bed of 2.47 % solids volume fraction provide both transient and steady measurements of chain deformation. Our results indicate that the flexible polyisobutylene polymers undergo a large conformation change, stretching in the direction of the average flow. This occurs even though the average flow in the bed is a plug flow which would not cause any polymer stretch by itself. The polymer stretch or conformation change increases with the number of chain interactions with bed fibres and ultimately reaches a steady-state value that can be correlated with the pore-size Deborah number (i.e. a characteristic polymer relaxation time divided by a characteristic flow time in the bed pore). Large changes in the polymer conformation are noted for values of the Deborah number, De 〉 5. In addition, the time to steady state scales with the characteristic flow time within a pore over a large range of Deborah numbers. The pressure drop across the fibre bed was also measured simultaneously with the birefringence measurement and was found to be directly proportional to the birefringence throughout the range of De investigated. Thus, we show empirically, for the first time, that chain elongation, which produces normal stress anisotropy within the fluid, is directly responsible for the increased flow resistance. These findings are then analysed in the light of recent theories for the response of polymer molecules in fixed bed flow fields (Shaqfeh & Koch 1992). It is shown that our results are consistent with the interpretation that these flows are stochastic strong flows, which create an apparent ‘coil-stretch’ transition. After extending the theory of Shaqfeh & Koch to account for the specifics in the experiments, including the bed geometry and statistics as well as the polydispersity of the polymer solutions, it is shown that the theory can predict most of the experimental results both qualitatively and quantitatively. © 1994, Cambridge University Press. All rights reserved.

Description: The existence of an organized streamwise vortical structure, which is superimposed on the well known coherent spanwise vorticity in nominally two-dimensional free shear layers, has been studied extensively. In the presence of stratification, however, buoyancy forces contribute to an additional mechanism for the generation of streamwise vorticity. As the spanwise vorticity layer rolls up and pulls high-density fluid above low-density fluid, a local instability results. The purpose of the current investigation is to force the three-dimensional instability in the stratified shear layer. In this manner, we experimentally observe the effect of buoyancy on the streamwise vortex tube evolution, the evolution of the buoyancy-induced instability, and the interaction between these two vortical structures. A simple numerical model is proposed which captures the relevant physics of the flow evolution. It is found that, depending on the location, streamwise vortices resulting from vortex stretching may be weakened or enhanced by the stratification. Buoyancy-induced vortex structures are shown to form where the unstable part of the interface is tilted by the streamwise vortex tubes. These vortices strengthen initially, then weaken downstream, the timescale for this process depending upon the degree of stratification. For initial Richardson numbers larger than about 0.03, the baroclinically weakened vortex tubes eventually disappear as the flow evolves downstream and the baroclinically generated vortices dominate the three-dimensional flow structure. © 1994, Cambridge University Press. All rights reserved.

Description: A flagellated, bottom-heavy micro-organism's swimming direction in a shear flow is determined from a balance between the gravitational and viscous torques (gyrotaxis). Hitherto, the cell has been assumed to be a spheroid and the flagella have been neglected. Here we use resistive-force theory to calculate both the magnitude and the direction of a biflagellate cell's swimming velocity and angular velocity relative to the fluid when there is an arbitrary linear flow far from the cell. We present an idealized model for the flagellar beat but, in calculating the velocity of the fluid relative to an element of a flagellum, the presence of the cell body is not neglected. Results are given for the case of a spherical cell body whose flagella beat in a vertical plane, when the ambient linear flow is in the same vertical plane. Results show that resistive-force theory can be used for organisms where the cell body has significant effect on the flow past the flagella and that the viscous torque on the flagella is a significant term in the torque balance equations. A model is presented for the calculation of a cell's velocity and angular velocity in a shear flow which is valid up to high magnitudes of rate of strain or vorticity. The main application of the results will be to modify a recent continuum model for suspensions of gyrotactic micro-organisms (Pedley & Kessler 1990). © 1994, Cambridge University Press. All rights reserved.

Description: The natural occurrence of Tollmien-Schlichting (TS) waves has so far only been observed in boundary layers subjected to moderate levels of free stream turbulence (Tu 〈 1%), owing to the difficulty in detecting small-amplitude waves in highly perturbed boundary layers. By introducing controlled oscillations with a vibrating ribbon, it is possible to study small-amplitude waves using phase-selective filtering techniques. In the present work, the effect of TS-waves on the transition is studied at Tu — 1.5%. It is demonstrated that TS-waves can exist and develop in a similar way as in an undisturbed boundary layer. It is also found that TS-waves with quite small amplitudes are involved in nonlinear interactions which lead to a regeneration of TS-waves in the whole unstable frequency band. This results in a significant increase in the number of turbulent spots, which promote the onset of turbulence. © 1994, Cambridge University Press. All rights reserved.