ALBERT

Description: In Moreton Bay, Queensland, the catch obtained using monofilament polyamide (PA) otter trawl-nets with multifilament polyethylene (PE) cod ends was compared with that obtained using multifilament PE trawl-nets of identical mesh opening (38 mm). Monofilament PA otter trawl-nets retained fewer small prawns ( 〈 24 mm carapace length) than conventional multifilament PE nets, but both nets caught similar quantities of larger prawns ( 〉 24 mm carapace length). The higher retention rate of small prawns by multifilament PE gear was reflected in the greater catch weights of Peraeus plebejus, Metapenaeus bennettae and Metapenaeopsis novaeguineae in those nets. Catch weights of larger prawn species such as Penaeus esculentus and Metapenaeus endeavouri did not differ between nets. Winter whiting (Sillago maculata) and squid (Loligo spp.) were trawled in similar abundance in both nets, although the monofilament retained fewer squid 〈 50 mm mantle length. More marketable ( 〉 15 cm carapace width) sand crabs (Portunus pelagicus) were caught in the monofilament net. There was not significant difference in the trash (noncommercial component) weight caught in both nets. Over the range of towing speeds tested (1.7–2.3 kn), use of monofilament nets significantly reduced total gear drag.

Description: ln the past, analysis of habitat choice by marine nekton has been hampered by limited access to its environment. We suggest a method to facilitate study of habitat choice, using data gathered from videotapes. The aims of this study were (a) to identify members of a particular nekton assemblage, and (b) to identify environmental variables important to the assemblage as a whole. Data on species and environmental variables came from Videotapes of a sandy-bottom shelf area (60m depth) in the Gulf of Mexico off Pensacola, Florida, taken by a remote-controlled submersible travelling along defined transects. We analyzed these Videotapes to derive Information on habitat use of several species of fishes and large invertebrates. We divided the transects into sections which were homo· geneaus for bottom type and algal coverage, and in each section measured habitat variables and abundances of the most common and reliably identifiable species of demersal nekton. Factor analysis of species' means for environmental variables identified patterns of habitat use among these species. The analysis identified these patterns by generating axes that represented environmental gradients. The patterns of habitat use by these species related to their preferences for different amounts of three·dimensional structure, algae, and infaunal and epifaunal organisms. We compared species distributions and habitat distributions on these axes to find which environmental gradients were of most importance in habitat selection by these species. We found that more species selected habitats on the basis of particular amounts of structure, fewer selected on the basis of algal coverage and infaunal organisms. Only one species seemed to select habitats on the basis of types or abundances of epifaunal organisms. Thus, amount of three-dimensional structure seemed an important variable to the sandy·bottom assemblage overall, followed by amount of algal coverage and types of infaunal organisms.

Description: We compared the diets of 4 CO-occurring species of penguin at sub-Antarctic Marion Island in light of mechanlsn~s thought to result in dietary differentiation. Calculation of overlap indices and correspondence analyses indicated a clear separation in the diets of the 3 penguin genera but considerable similarity between the congeneric species pair The pelagic foraging king penguin Aptenodytes patagonicus consumed mainly myctophid fish, whereas the near-to offshore foraging macaroni penguin Eudyptes chrysolophus and rockhopper penguin E. chrysocome both consumed predominantly small pelagic crustaceans, although in different proportions. The inshore foraging gentoo penguin Pygoscelis papua fed largely on benthic nototheniid fish. Although king penguins rarely take small prey, differences in diet cannot be accounted for solely on the basis of prey size selection. Different diving capabilities may have some role in dietary differentiation, however, we consider prey availability in the apparently distinct feeding zones to explain most of the differences in the diets of the 4 species of penguins at Marion Island. The daily population food requirements of the respective penguin species at the Prince Edward Islands (comprising Marion and Prince Edward islands) increased with Increasing species foraging range. The mainly benthic nature of the prey in the inshore area, compared with the more easily replenished pelagic food stocks, probably explains the differences in food ava11abi.lity that sustain the greater food demands of the large populations of pelagic and offshore foragers.

Description: Sperm whales Physeter macrocephalus were observed off the Galapagos Islands between late February and April 1985, a year of cool sea-surface temperatures (SST), and January to June 1987, an 'El Nino' year of warm SST Distribu- tlon, abundance and diet of sperm whales were similar in both years. However, in 1987 they appeared to have a lower feeding success, as ind~cated by a reduced rate of observing faeces, and dived to shallower depths. Excretion rates were negatively correlated with sea-surface temperatures.

Description: Thirteen types of octopodid paralarvae are recognized from Hawaiian waters, although the adults of only seven species (three are undescribed) are currently known from this area. The most common 11 paralarval types are described; five types can be identified with known adults. Stage II paralarvae differ from Stage I paralarvae by the presence of sucker buds on their arms. The number of suckers in Stage I paralarvae is characteristic for a species, as are their chromatophore patterns. Hatchlings have a high density of integumental pores containing secretory granules that may produce a mucous “drogue” to assist in offshore transport.

Description: Characteristics of water masses were analyzed to study the Kuroshio intrusion into the sea southwest of Taiwan. Hydrographic data were obtained from CTD (conductivity, temperature, and depth) casts during two cruises in May and August 1986. In May, remnants of water intruding from the Kuroshio were found on the continental slope south of the Penghu Channel. By August, these were replaced by water from the South China Sea. During this period, water from the Kuroshio also appeared near the southern tip of Taiwan. The intrusion current reached a depth of at least 500 m and was probably part of a cyclonic circulation in the northern South China Sea. The results support the hypothesis of a seasonal pattern of the intrusion process: intrusion of water from the Kuroshio begins in late summer, intensifies in winter, and ceases by late spring when South China Sea waters again enter this region.

Description: Kurzfassung eines Vortrages zum Polartag in Bremerhaven am 23.2.1988

Description: Combined Sr-Nd-Pb isotope and trace-element data for St Helena are interpreted in terms of changing thermal and chemical fluxes impinging on and interacting with the base of the lithosphere over a period of 6 Ma. The data reveal the existence of two geochemically distinct components in the St Helena source region: (i) a HIMU (high U/Pb) component which has extremely radiogenic lead isotopes (206Pb/204Pb 〉20.8) with 87Sr/86Sr and 143Nd/144Nd ratios displaced below the mantle array; (ii) a component with less radiogenic lead and strontium isotopic compositions and more radiogenic neodymium compositions. Coupled trace-element and isotope variations are evident during the activity of each volcano. During shield development an increase in incompatible-trace-element enrichment occurs. This is coupled to a decrease in 143Nd/144Nd, whilst strontium and lead isotope ratios become progressively more radiogenic with time. The time-dependent variations are thought to be consistent with high-level processes occurring at the base of, or within, the lithosphere. A decrease in the signature of the depleted component with time is shown to be the result of a decreasing thermal flux acting on the base of the lithosphere. As a consequence the degree of partial melting of the depleted component (which may reside in the lithosphere or asthenosphere) is reduced, increasing the signature of the HIMU component in the erupted magmas.

Description: The importance of feeding pattern is well documented in fish (Jenkins & Green, 1977; Simenstad & Cailliet, 1986) but there are not many reported studies in cephalopods. Feeding patterns, as defined by Jenkins & Green (1977) have been studied, to our knowledge, only in Todarodes pacificus (Okiyama, 1965), Loligo pealei (Vovk, 1972), Loligo opalescens (Karpov & Cailliet, 1978), Illex illecebrosus (Amaratunga et ah, 1979; Amaratunga, 1980) and Nototodarus gouldi (O'Sullivan & Cullen, 1983). Boyle (1983) dealt with aspects of feeding in several cephalopod species but not specifically with feeding pattern. Aspects of feeding in Sepia officinalis have been reviewed by Nixon (1987). The present work describes the daily feeding pattern in Sepia officinalis from data collected in the field.

Description: The diets of five breeding seabird species were investigated on Adélie Land in January–February 1982. Stomach contents of Adélie penguins, Pygoscelis adeliae, were sampled by a water off-loading method and of Procellariiformes by spontaneous regurgitation. Diet compositions by mass were: Adélie penguin (79% euphausiid, 18% fish, 3% squid); Cape pigeon, Daption capense, (64% euphausiid, 29% fish, 7% carrion); Antarctic fulmar, Fulmarus glacialoides, (64% euphausiid, 20% carrion, 16% fish); snow petrel, Pagodroma nivea, (95% fish, 2% euphausiid, 1% carrion) and Wilson's stormpetrel, Oceanites oceanicus, (39% fish, 37% euphausiid, 13% carrion, 12% various crustaceans). The present Adélie penguin diet is consistent with those reported in other studies, given our knowledge of geographical variation in food availability. Differences in the diets of fulmarine petrels appear to relate to differences in foraging areas. The snow petrel is a fish-eating bird associated with pack-ice. Cape pigeon and Antarctic fulmar are mainly krill-eaters and we infer segregation along a neritic/oceanic gradient because of the importance of the neritic Euphausia crystallorophias in the former and the oceanic E. superba in the latter.

Description: Se describen los resultados del estudio ecolögico de las especies mäs abundantes pertenecientes a las familias Ommastrephidae y Loliginidae del A tlä n tic o Sudoeste. Las investigaciones fueron (levadas a cabo por cienti'ficos sovieticos entre 1981 y 1987. Se presta especial atencion a Ille x argentinus. Se presenta informaciön sobre la frecuencia biotöpica, ciclos de vida, duraciön de vida, biologia reproductiva y fauna de los paräsitos. Asimismo se discute el problema de su estructura intraespeci'fica.

Description: A collection of 130 specimens of Sepiola (ligulata, robusta, rondeletii, intermedia), 115 Rondeletiola minor, 90 Sepietta ( obscura, neglecta) and more abundant samples of S. oweniana obtained by trawl fishing in the Ligurian Sea are briefly illustrated in terms of depth distribution, sex ratio and maturity stages.

Description: Santorini volcanic field has had 12 major (1–10 km3 or more of magma), and numerous minor, explosive eruptions over the last ~ 200 ka. Deposits from these eruptions (Thera Pyroclastic Formation) are well exposed in caldera-wall successions up to 200 m thick. Each of the major eruptions began with a pumice-fall phase, and most culminated with emplacement of pyroclastic flows. Pyroclastic flows of at least six eruptions deposited proximal lag deposits exposed widely in the caldera wall. The lag deposits include coarse-grained lithic breccias (andesitic to rhyodacitic eruptions) and spatter agglomerates (andesitic eruptions only). Facies associations between lithic breccia, spatter agglomerate, and ignimbrite from the same eruption can be very complex. For some eruptions, lag deposits provide the only evidence for pyroclastic flows, because most of the ignimbrite is buried on the lower flanks of Santorini or under the sea. At least eight eruptions tapped compositionally heterogeneous magma chambers, producing deposits with a range of zoning patterns and compositional gaps. Three eruptions display a silicic–silicic + mafic–silicic zoning not previously reported. Four eruptions vented large volumes of dacitic or rhyodacitic pumice, and may account for 90% or more of all silicic magma discharged from Santorini. The Thera Pyroclastic Formation and coeval lavas record two major mafic-to-silicic cycles of Santorini volcanism. Each cycle commenced with explosive eruptions of andesite or dacite, accompanied by construction of composite shields and stratocones, and culminated in a pair of major dacitic or rhyodacitic eruptions. Sequences of scoria and ash deposits occur between most of the twelve major members and record repeated stratocone or shield construction following a large explosive eruption. Volcanism at Santorini has focussed on a deep NE–SW basement fracture, which has acted as a pathway for magma ascent. At least four major explosive eruptions began at a vent complex on this fracture. Composite volcanoes constructed north of the fracture were dissected by at least three caldera-collapse events associated with the pyroclastic eruptions. Southern Santorini consists of pryoclastic ejecta draped over a pre-volcanic island and a ridge of early- to mid-Pleistocene volcanics. The southern half of the present-day caldera basin is a long-lived, essentially non-volcanic, depression, defined by topographic highs to the south and east, but deepened by subsidence associated with the main northern caldera complex, and is probably not a separate caldera.

Description: Between September 1987 and February 1988, Antarctic fur seals Arctocephalus gazella (Peters) at Heard Island fed mainly on fish with an average 95.2% of scats in monthly collections containing fish remains. Pelagic myctophids constituted more than 50% of fish taken by fur seals at the beginning of the summer season and again at the end when there was an influx of non-breeding male seals. During the middle period from October to December, fish from the surrounding shelf area comprised the bulk of the diet. These included various benthic nototheniid species, the bentho-pelagic ice fish Champsocephalus gunnari Lönnberg and skate (Bathyraja spp.), the latter being found in over 60% of scats in October and November. The population of Antarctic fur seals at Heard Island is increasing at about the same rate as at South Georgia. There the increase is thought to be due to the high availability of krill E. superba, but in the present study no euphausiid remains were found, so the increasing population at Heard Island has been supported on a diet of fish. Whether this population increase can be sustained in future on a diet of fish is arguable. Trial fishing around Heard Island indicates that one of the major dietary items of the seals (C. gunnari) is of probable commercial importance and therefore any plans for the establishment of a fishery on Heard Island grounds must be considered in this light.

Description: Metabolism not only affects the acid–base status of an animal by means of proton stoichiometries but, by feedback regulation, acid–base parameters (pH, , bicarbonate) influence metabolic rates and the pathways used. This leads to a significant contribution of metabolism to acid–base regulation under both aerobic and anaerobic conditions. The relationship between amino acid metabolism, urea synthesis, and excretion is discussed as an example important for steady-state metabolic acid–base regulation during aerobiosis. Generally, acid–base relevant metabolism may be regulated through the effect of acid–base disturbances on hormonal mediation, allosteric modulation of enzyme proteins, pH optima, and the levels of substrates or products, some of these being acid–base relevant substances like bicarbonate, CO2, inorganic phosphate, and NH3. During functional or environmental anaerobiosis the same relationships prevail. Metabolic proton accumulation is counterbalanced by phosphagen depletion and ammonia accumulation in adenylate catabolism. In addition, in integrated control of metabolic and acid–base status, long-term (mitochondrial) anaerobiosis leads to reductions in metabolic rate and increased removal of acidic groups. The importance of metabolic processes in acid–base methodology is discussed in terms of traditional concepts and recent developments.

Description: Der Einfluß lateralen Stresses auf die mechanische Diagenese von marinen Sedimenten kann mithilfe sedimentphysikalischer Daten quantifiziert werden. Beispielhaft wurde dies anhand von Daten aus dem Deep Sea Drilling Project (DSDP) und Ocean Drilling Project (ODP) für den Akkretionskeil des Barbados Ridge Complex durchgeführt. Die Untersuchung erfolgte in drei Schritten. (1) In einer statistischen Untersuchung der umfangreichen sedimentologischen und sedimentphysikalischen Datenbank des DSDP wurden tief enabhängige Funktionen der mechanischen Diagenese für eine Reihe von lithologischen Standardtypen definiert. Diese, als Referenzgröße zur Quantifizierung der tektonischen KonsoHdation in einem rezenten Akkretionskeil benötigten Funktionen, wurden in erster Linie für pelitische und psammitische Sedimente mit geringen Karbonatgehalten entwickelt. Zwei verschiedene Verfahren zur Auswahl von entsprechenden Datensätzen werden beschrieben und die Ergebnisse der statistischen Untersuchung mit den in der Literatur beschriebenen Funktionen verglichen. (2) Die entwickelten Typfunktionen wurden bei der Durchführung eines palinspastischen Rekonstruktionsverfahrens benutzt, mit dem die Entwicklung sedimentphysikalischer Parameter während der initialen Deformationsphase in rezenten Akkretionssystemen modelliert werden konnte. Diese Untersuchung basierte im wesentlichen auf sedimentphysikalischen Daten der DSDP- und ODP-Legs 78A und J 10 (Barbados Ridge Komplex, Kleine Antillen). Durch palinspastische Entzerrung der imbrikierten Schuppung und stratigraphische Rekonstruktion akkretierter "thrust slices" im untersuchten Bereich, entsprechender Relozierung der zugehörigen sedimentphysikalischen Daten und dekompaktive Anpassung an die rekonstruierte Position konnte ein synthetisches prä-akkretionäres Profil der ursprünglichen Porosität rechnerisch modelliert werden. (3) Der Vergleich dieses synthetischen Porositäts-Tiefen-Profils mit charakteristischen Referenzprofilen aus undeformierten Sequenzen unmittelbar vor der Deformationsf ront zeigt eine systematische, lithologisch bestimmte Divergenz. Durch Überarbeitung des Rekonstruktionsverfahrens mithilfe von Stress-PorositätsBeziehungen konnte der relative und absolute Einfluß der lateralen Stresskomponente auf die Konsolidation hemipelagischer Sedimente in diesem Teil des konvergenten Plattenrandes quantifiziert werden.

Description: One method of testing the concept of sequence stratigraphy is to compare it to Quaternary sediments in which chronology, stratigraphic relations, and facies geometry are more clearly understood than in older rocks. Rapid deposition rates during Quaternary glacial-eustatic cycles in large deltaic depocenters generate sequences comparable to those in the ancient stratigraphic record. In the northern Gulf of Mexico, the late Wisconsinan-Holocene Mississippi River has deposited a Type 1 sequence that includes lowstand, transgressive, and high-stand systems tracts. Characteristics of modern Mississippi River sedimentary environments support the methodology used in sequence analysis, but the short time taken for sequence generation here raises important questions about sequence time scales, correlation, and driving mechanisms.

Description: RECENT advances in 40Ar/39Ar dating1,2 have made it possible to date individual K-feldspar grains from Pleistocene tephra, a capability that greatly improves the reliability and temporal resolving power of the method. Here we apply these new techniques to the dating of a phonolite tephra from the East Eifel volcanic field in West Germany, which is sandwiched between loess and palaeosol (alfisol) deposits, and which was therefore erupted during the transition from a glacial to an interglacial period. Our age estimate for this transition is 215±4 kyr (1 σ), which has important implications for the marine δ18O timescale and for models of global climate change during the Pleistocene. The results show that single-grain dating can detect and compensate for the large quantities of xenocrystic contaminants which are found in many tephra deposits. This technique could be used to date the tephra layers found in marine sediment cores and the results could greatly enhance the reliability of the marine δ18O timescale for more rigorous Fourier analysis testing of the Milankovitch hypothesis.

Description: A seismic refraction profile recorded along the geologic strike of the Chugach Mountains in southern Alaska shows three upper crustal high-velocity layers (6.9, 7.2, and 7.6 km/s) and a unique pattern of strongly focussed echelon arrivals to a distance of 225 km. The group velocity of the ensemble of echelon arrivals is 6.4 km/s. Modeling of this profile with the reflectivity method reveals that the echelon pattern is due to peg-leg multiples generated from with a low-velocity zone between the second and third upper crustal high-velocity layers. The third high-velocity layer (7.6 km/s) is underlain at 18 km depth by a pronounced low-velocity zone that produces a seismic shadow wherein zone peg-leg multiples are seen as echelon arrivals. The interpretation of these echelon arrivals as multiples supersedes an earlier interpretation which attributed them to successive primary reflections arising from alternating high- and low-velocity layers. Synthetic seismogram modeling indicates that a low-velocity zone with transitional upper and lower boundaries generates peg-leg multiples as effectively as one with sharp boundaries. No PmP or Pn arrivals from the subducting oceanic Moho at 30 km depth beneath the western part of the line are observed on the long-offset (90-225 km) data. This may be due to a lower crustal waveguide whose top is the high-velocity (7.6 km/s) layer and whose base is the Moho. A deep (~54 km) reflector is not affected by the waveguide and has been identified in the data. Although peg-leg multiples have been interpreted on some long-range refraction profiles that sound to upper mantle depths, the Chugach Mountains profile is one of the few crustal refraction profiles where peg-leg multiples are clearly observed. This study indicates that multiple and converted phases may be more important in seismic refraction/wide-angle reflection profiles than previously recognized.

Description: The presence of the cephalopods H. dispar and 0. banksii in the Gulf of Taranto (Ionian Sea, Mediterranean) is recorded here. One specimen of each species was found in the gastric content of two different swordfish; two more specimens of H. dispar were obtained from the starnach of a flying squid, Todarades sagittatus, wich in turn had been preyed upon by one of those swordfish.

Description: The foraging behaviour of fur seals and two species of surface feeding seabirds was observed over swarms of vertically migrating krill along the Antarctic Peninsula in July 1987. Fur Seal haul out patterns were correlated with krill in the upper 30 m of the water column. Krill moved to the surface at night; seals subsequently foraged from 1400-0700 hours before returning to floes. Foraging was continuous through the night. Dive duration decreased as krill moved up to the surface; shorter dives may have been more successful than longer ones. It is possible that very deep dives, which occur early in a foraging bout, represent more of an attempt to assess krill depth and distribution rather than being a genuine foraging effort. Seabirds responded to the presence of a surface krill swarm by circling over it and foraging; krill at depths greater than 30 m elicited directional flight and low frequencies of prey capture attempts. Both Snow Petrels and Antarctic Terns preyed on krill, but each species approached the swarms from different habitats. Snow Petrels primarily overflew areas covered by ice; terns preferred open water. This suggested that prey encounters are essentially opportunistic, although the search for prey is limited to rather specific marine habitats. This feature may be important to our understanding of the factors that determine the pelagic distribution of seabirds.

Description: The diet of the Gentoo Penguin Pygoscelis papua at sub-Antarctic Marion Island was sampled by stomach pumping at monthly intervals from March 1984 to March 1985. Overall, fish accounted for 53% of the diet by mass, crustaceans 44% and cephalopods 2%. Crustaceans predominated between March and June 1984; a marked increase in the proportion of fish in July coincided with the start of egg laying by Gentoo Penguins. Fish accounted for almost all of the diet in January and March 1985. Juvenile nototheniid fish, in particular Notothenia squamifrons, formed the bulk of the fish component; myctophids and Channichthys rhinoceratus were less common. The pelagic euphausiid Euphausia vallentini accounted for about 50% by mass of the overall crustacean component lumped over the entire study period. The decapod shrimp Nauticaris marionis was the most important crustacean species consumed during June to September 1984. Cephalopods, predominantly octopods, were taken mainly in February and March 1985. The hypothesis that seasonal changes in diet occur in direct response to the arrival of crested penguins (Eudyptes spp) early in summer is not supported by the data. Changes in diet appear to reflect local changes in the availability of prey species within the inshore waters exploited by Gentoo Penguins.

Description: Experimental feeding of Yellow-eyed Penguins (Megadyptes antipodes) with meals containing cephalopod beak pairs and otoliths of known weight, and subsequent flushing of stomachs at 2-48 h intervals after feeding, were carried out to determine the rate of digestion of beaks and otoliths. Otoliths and beaks were placed in HCl to observe changes. All otoliths were totally digested after 24 h in penguin stomachs, disappearance rate was inversely related to size of the otolith. After 24 h squid beaks showed increasing signs of wear, the extent of which was dependent on the presence or absence of small stones in the stomach. Experiments showed that HCl only causes otolith erosion at pH 1.5; erosion rate was twice as slow as in the stomachs. Acid had no effect on squid beaks after 78 h immersion. /// Se llevó a cabo alimentación experimental de pingüinos (Megadyptes antipodes) con comida previamente pesada que contenía otolitos y picos de cefalópodos, para determinar la velocidad de digestión de picos, y de picos-y-otolitos. Para determinar la velocidad de digestión se lavó el estómago de las aves utilizando la técnica de Wilson (1984) a intervalos de 2-48 h, una vez los pingüinos eran alimentados. Otolitos y picos fueron también colocados en HCl para observar cambios en estos. Los otolitos fueron totalmente digeridos luego de pasar 24 h en el estómago de los pingüinos. La velocidad de desaparición fue inversamente proporcional al tamaño del otolito. Después de 24 h los picos de los calamares mostraban signos de desgaste; la extención del desgaste estuvo relacionado con la presencia o ausencia de gúijaros en el estómago de los pingüinos. Los experimentos in vitro demostraron que el HCl solo causa erosión de los otolitos a un pH de 1.5; la velocidad de erosión resultó ser dos veces más lenta que en el estómago de los pingüinos. Los picos de calamares no se afectaron después de estar sumergidos por 78 h en ácido.

Description: Sediments on high Arctic shelves result from modern processes and the effect of former glaciations. Based on data from the northern Barents Sea, an area with input from large and numerous surging glaciers, we define two principal zones with different environmental regimes and corresponding sedimentary facies: (1) a glacier-proximal zone influenced by grounding-line processes and the immediately adjacent areas affected by glacial sediment input, and (2) a glacier-distal, sea-ice and current-controlled zone, which also includes a wide sediment-starved region dominated by biogenic carbonate accumulation. Characteristic of the glacier-proximal zone are glacial surges which affect sedimentation rates and leave a diagnostic pattern of sea-floor morphologies. Extensive ice gouging causes a homogeneous sediment texture. In the glacier-distal zone, fine-grained mud supplied from sea ice and infrequent coarser material deposited from icebergs is reworked by modern oceanographic processes. On shallow banks, in 30–50 m of water, carbonates accumulate from a prolific bottom fauna formed in response to extensive reworking and nutrient supply.

Description: During a seismic reflection survey conducted by the California Consortium for Crustal Studies in the Basin and Range Province west of the Whipple Mountains, SE California, a piggyback experiment was carried out to collect intermediate offset data (12–31 km). These data were obtained by recording the Vibroseis energy with a second, passive recording array, deployed twice at fixed positions at opposite ends of the reflection lines. The reflection midpoints fall into a 3-km-wide and 15-km-long region in Vidal Valley, roughly parallel to a segment of one of the near-vertical reflection profiles. This data set makes three unique contributions to the geophysical study of this region. (1) From forward modeling of the observed travel times using ray-tracing techniques, a shallow layer with velocities ranging from 6.0 to 6.5 km/s was found. This layer dips to the south from 2-km depth near the Whipple Mountains to a depth of 5-km in Rice Valley. These depths correspond closely to the westward projection of the Whipple detachment fault, which is exposed 1 km east of the near-vertical profiles in the Whipple Mountains. (2) On the near-vertical profile, the reflections from the mylonitically deformed lower plate at upper crustal and mid crustal depths are seen to cease underneath a sedimentary basin in Vidal Valley. However, the piggyback data, which undershoot this basin, show that these reflections are continuous beneath the basin. Thus near-surface energy transmission problems were responsible for the apparent lateral termination of the reflections on the near-vertical reflection profile. (3) The areal distribution of the midpoints allows us to construct a quasi-three-dimensional image on perpendicular profiles; at the cross points we determined the true strike and dip of reflecting horizons. This analysis shows that the reflections from the mylonitically deformed lower plate dip to the southwest westward of the Whipple Mountains and dip to the south southward of the Turtle Mountains. The results of this study support the interpretation of crustal reflectivity in the near-vertical reflection profiles to be related to the mid-Tertiary episode of extension which produced the Whipple metamorphic core complex. This association geometrically suggests a more regionally distributed mechanism for crustal thinning as compared with single detachment fault models.

Description: Five major alteration zones in the Extrusive Series and the Sheeted Dike Complex of the Troodos Ophiolite are each characterized by (a) distinct elemental changes compared to the original composition and (b) secondary mineralogy. The upper ca. 300 m of the extrusive crust, the highly oxidatedcold seawater alteration zone (CSA), is strongly enriched in K2O and depleted in Na2O. It is followed downwards by alow temperature alteration zone (〈170° C) which is most widespread in the Troodos extrusives and where Na2O and K2O are enriched, the latter less strongly than in the CSA zone. Three types ofhigh temperature alteration zones (〈440° C; HTA I–III) are found in the Sheeted Dike Complex. All are marked by thorough leaching of K2O, while the behavior of Na2O (e.g. unchanged in type III) and CaO (depleted in type I, enriched in types II, III) is variable. Mass budgets of elemental changes are quantified by calibration of whole rock analyses via systematic stable element variations of fresh glasses found throughout the extrusive section. The Troodos extrusive crust and upper Sheeted Dike Complex are a major sink for MgO, K2O, and Na2O, and a source for CaO; the overall scale of fluxes drastically exceeds estimates based on fresh basalt compositions from present ocean crust.

Description: Zur Ableitung der Bodenalbedo aus METEOSAT - Daten müssen verschiedene Korrekturen vorgenommen werden: a)eine Wolkenelimination, b) eine Atmosphären-, c) eine Winkelkorrektur und d) eine spektrale Korrektur. Zur Wolkenerkennung wurde ein Extremwertverfahren entwickelt, das gleichzeitig eine Minimierung des Atmosphäreneinflusses bewirkt. Nach Anwendung dieses Verfahrens muß nur noch ein kleiner Einfluß der Atmosphäre behandelt werden. Für die Korrekturen im wolkenfreien Fall wurde mit Strahlungstransportsimulationen ein synthetischer Datensatz bestehend aus gefilterter und ungefilterter Bodenalbedo, METEOSAT - Strahldichte, Gesamtwasserdampfgehalt, optischer Dicke der Atmosphäre und dem Anisotropiefaktor am Boden erzeugt. Die multivariate Analyse des Datensatzes ergab als Auswertemodell einen linearen Zusammenhang zwischen gefilterter Bodenalbedo (Bodenalbedo im METEOSAT - Kanal), METEOSAT - Strahldichte, Gesamtwasserdampfgehalt, optischer Dicke und Anisotropiefaktor am Boden. Unter Berücksichtigung realistischer Fehler der Eingangsgrößen kann hiermit eine kombinierte Atmosphären- und Anisotropiekorrektur erfolgen. Das breite Spektrum an Reflexionseigenschaften, das in der Analyse berücksichtigt wurde, sowie der nach der Anwendung des Extremwertverfahrens geringe Atmosphäreneinfluß bewirken, daß die Atmosphärenparameter verglichen mit dem Anisotropieverhalten der Oberfläche nur eine untergeordnete Rolle spielen. Die Analyse des Datensatzes ergab gleichfalls einen linearen Zusammenhang zwischen ungefilterter und gefilterter Bodenalbedo, wobei im wesentlichen das spektrale Reflexionsvermögen der Oberfläche und weniger die Atmosphäre bestimmend ist. Bei Berücksichtigung von Zusatzinformationen beträgt die Genauigkeit der solaren Bodenalbedo 0.04 bis zu einem Sonnenzenitwinkel von 66.45° und für die meisten Blickwinkelgeometrien. In der Anwendung konnte für den Januar und Juni 1983 11:30 UT gezeigt werden, daß die Bodenalbedo über Afrika bei hohem Sonnenstand mit genügender Genauigkeit auch ohne Zusatzinformationen abgeleitet werden kann. Der maximale Fehler im Juni beträgt 0.03 und im Januar 0.034. Im Vergleich mit ebenfalls aus Satellitendaten abgeleiteten Werten der Bodenalbedo anderer Autoren in der westafrikanischen Sahelzone lagen die hier abgeleiteten Werte etwas niedriger, in einigen Fällen stimmten sie innerhalb der angegebenen Fehlergrenzen überein. Vergleiche mit in-situ Messungen der Bodenalbedo in der Sahara über sechs verschiedenen Oberflächen ergab in zwei Fällen eine gute Übereinstimmung innerhalb der Fehlergrenzen, bei den anderen traten größere Differenzen auf.

Description: Cephalopod beaks in the regurgitations of wandering albatross chicks from the breeding colony at Bird Island, South Georgia were collected throughout the austral winters of 1983 and 1984. There were large changes in relative frequency of species between the two years. In 1984 there were fewer Antarctic species in the bird's diet and more species which are known to occur to the north of the Sub-Antarctic Front. Notably, the proportion of an Illex sp. increased from 11% to 33% by number. Illex sp. was absent from a collection of cephalopod beaks from wandering albatross chick regurgitations made in 1976-77. The nearest known stock of this genus is Illex argentinus, which occurs over the Patagonian shelf. The data indicate that in 1984 the wandering albatrosses were exploiting a warmer water cephalopod community. Either their foraging range was extended further to the north and west in that year or there was a south easterly incursion of water from the South Atlantic which carried warmer water cephalopods closer to Bird Island. Sea-surface temperature records (NOAA, Climate Analysis Center) show no evidence of an incursion of warm water in 1984. On the contrary, in 1984 sea surface temperatures were cooler than in 1983. It is proposed that the collapse of the krill population in the vicinity of South Georgia, reported in the literature for the 1983 austral winter, resulted in sufficient disruption of the food web in the region to cause the wandering albatrosses to extend their foraging range in the austral winter of 1984.

Description: Age and growth parameters of the tropical loliginid squid sepioteuthis lessoniana in eastern Australian waters were determined from statolith growth-ring analysis. Juvenile specimens were captured, maintained alive, and their statoliths were chemically makred in situ with either tetracycline or calcein. These chemicals produced a flourescent mark within the statolith microstructure when viewed under UV light. Statoliths were mounted in thermoplastic cement and subsequently ground and polished. This process allowed rings to be visualized without any further preparation. It was thus possible to validate that distinct statolith rings were formed daily and that less-distinct thinner rings were, in fact, subdaily rings. The results of the age analysis of field-captured individuals revealed that the population of S. lessoniana in the study area grows at a very fast rate. Maturity in both sexes was achieved in less than 100 days. All specimens aged were less than 6 months old. The size of large individuals was within the range of S. lessoniana captured in other areas, with size ranges being 75-213 mm and 75-184 mm for males and females, respectively. Growth rates determined for S. lessoniana based on statolith ageing are considerably different from previous estimates based on length frequency data.

Description: Las capturas de calamar (Ille x argentinus) de cinco campanas de investigaciön realizadas por el B /l Oca Balda fueron procesadas mediante el metodo de ärea barrida para obtener estimaciones (en peso y nümero de individuos) de las densidades en cada lance de pesca. Utilizändose estratos de finidosa p r io r i sobre la base de la abundancia relativa de la merluza comün (Merluccius hubbsi), se realizaron las estimaciones de la biomasa del calamar, en peso y nümero, correspondientes a las campanas del ano 1986 y a la OB-03/87. Igualmente se suministra la evaluaeiön de calamar en mayo de 1987 pero sobre estratos de fin id o sa p r io r i relacionados con las zonas de concentraciön de calamar de anos anteriores.

Description: Durante diciembre de 1986 y enero-febrero de 1987, el B/l Oca Balda realizo dos cruceros de investigacion en aguas de la plataforma Continental patagonica. El primero (OB-07-86), operö en el sector norpatagonico entre las isobatas de 50 y 100 m, teniendo como objetivo la evaluacion del stock desovante de merluza comün (Merluccius hubbsi). El segundo (OB-Ol-87), explorö las aguas de la plataforma subpatagönica desde los 46°S hasta los 55°S por fuera del ärea de exclusion de las Isias Malvinas, y tuvo por objetivo la evaluacion de las principales especies de interes comercial.

Description: Humboldt Penguins diving in clear water in Chile had two distinct behaviours; short dives (x¯=13.3s)(x¯=13.3s) where the birds remained within a metre of the surface and bounce dives, where the penguins descended the water column to the sea bed where they immediately returned to the surface. Here, dive time was correlated with water depth. Stomach pumped penguins had eaten predominantly pelagic school fish,Scomberesox, Engraulis andSardinops. Most prey (94 %) had been seized from below. We suggest that short, shallow dives are typical of travelling penguins. Bounce dives, however, would enable foraging penguins, which have an enhanced binocular field above the line of the bill, to perceive surface-swimming prey more easily because silvery clupeid fish appear as silhouettes. In klaren Gewässern in Chile tauchende Humboldt-Pinguine zeigten zwei deutlich verschiedene Verhaltensweisen. Während kurzer Tauchgänge (x¯=13,3s)(x¯=13,3s) blieben die Tiere im Bereich von 1 m unter der Oberfläche. Tauchgänge durch unmittelbares Abtauchen in einem Winkel von 45° eingeleitet, führten direkt zum Meeresboden; die Vögel kehrten sofort wieder an die Oberfläche zurück. In diesem Fall war die Tauchzeit von der Wassertiefe abhängig. Pinguine, deren Magen durch Auspumpen untersucht wurde, hatten vorwiegend pelagische Schwarmfische gefressen:Scomberesox, Engraulis undSardinops. Die Mehrzahl der Fische (94 %) wurde von unten kommend erfaßt. Nach unserer Auffassung sind die kurzen und flachen Tauchgänge typisch für nicht jagende Pinguine, die längere horizontale Strecken zurücklegen. Das tiefe Abtauchen dagegen ermöglicht jagenden Pinguinen, die ein besonders gutes Fernsichtvermögen oberhalb des Schnabels besitzen, nahe der Oberfläche schwimmende Beute leichter zu erfassen. Die sonst silbrigen clupeiden Fische sind als dunkle Silhouetten gegen die Wasseroberfläche besser zu erkennen.

Description: Collections of Loligo pealei LeSueur, 1821 from the Atlantic seaboard between Cape Hatteras and Georges Bank differ significantly in both allele and genotype frequencies at the phosphoglucomutase locus. Loligo pealei collected off the coast of Virginia are distinct at this locus from all other areas surveyed. Loligo pealei collected from Georges Bank also differ significantly at this locus from those collected inshore off Cape Cod. These results suggest that L. pealei along the Atlantic seaboard consists of several distinct populations. A comparison of allele frequencies at nine allozyme loci among L. pealei, Loligo plei Blainville, 1823, and Lolliguncula brevis (Blainville, 1823) reveals that L. pealei differs completely from L. plei at five loci, L. pealei from L. brevis at six loci, and L. plei from L. brevis at three loci.

Description: Auszug aus einem Arbeitsbericht

Description: Geostrophic computations from historical data across the Brazil Current at 23° and 24°S lead to transports of 10.2 and 9.6 Sv, respectively. Data exist from all four seasons at about 24°S, but no seasonal signal can be seen in the baroclinic transport of the Brazil Current there. At 33°S the Brazil Current transport is estimated to be 17.5 Sv. A recirculation cell of 7.5 Sv is found in the western South Atlantic south of 28°S. The major problem in computing transport of the Brazil Current is not with determining the correct reference depth, but with the Brazil Current flowing partially over the shelf and therefore not being sampled completely by deep-water hydrographic stations. As long as the vertical distribution of water masses is taken into account for choosing a reference depth, geostrophic computations lead to results consistent with previous estimates.

Description: Historical data from the region between the Greenwich meridian and the African continental shelf are used to compute the offshore geostrophic transport of the Benguela Current. At 32°S, the Benguela Current is located near the African coast, transporting about 21 Sv (1 Sv = 106 m3 s−1) of surface water toward the north relative to a potential density surface lying between the upper branch of Circumpolar Deep Water and the North Atlantic Deep Watar. Two warm core eddies of probable Agulhas Current origin an observed west of the Benguela Current at 32°S. Near 30°S, the Benguela Current turns toward the northwest and begins to separate from the eastern boundary. It carries about 18 Sv of surface water across 28°S. The current then turns mainly toward the west to flow over a relatively deep segment of the Walvis Ridge south of the Valdivia Bank. A surface current with northward surface of about 10 cm s−1 flows along the western side of the Valdivia Bank, while another northward surface current flows at about 20 cm s−1 some 300 km west of the bank. About 3 Sv of surface now do not leave the Cape Basin south of the Vaidivia Bank, but instead drift northward as a wide. sluggish flow out of the northern end of the Cape Basin. Because of the more southerly seaward extensions of most of the Benguela Current, there are no deep-reaching interactions observed between this current and the cyclonic gyre in the Angola Basin east of the Greenwich meridian. Beneath the surface layer, about 4–5 Sv of Antarctic Intermediate Water are carried northward across 32° and 28°S by the Benguela Current, essentially all of which turns westward to cross the Greenwich meridian south of 24°S.

Description: The regions containing the two zonal currents of the subtropical gyre in the eastern North Atlantic, the Azores Current and the North Equatorial Current (NEC), have quite different physical characteristics. Associated with the Azores Current are strong horizontal thermohaline gradients that can be located easily both at the surface and at depth with temperature data alone, thus making satellite IR imagery and expendable bathythermograph profiles suitable for observing it. During winter, the surface expression of the Azores Current is often found to the north of the strongest subsurface gradients. In contrast to the Azores Current and to the central water mass boundary just to the south, the NEC has relatively weak horizontal temperature and salinity gradients, requiring density information in order to identify it. There is no clear surface manifestation found with the NEC. Common to both currents, though, is that each transports O(8 Sv) in the upper 800 m of the ocean near 27°W, with the largest velocities being in the upper 400 m.

Description: Five Ocean Drilling Program sites (657-661), which form a north-south transect off the western periphery of the Sahara, were selected. Nearshore mean flux of opal off Cap Blanc (21°N) showed an abrupt increase about 3 Ma that appears to reflect the main onset of coastal upwelling fertility and enhanced trade winds. At the same time, the input of river-borne clay strongly decreased, suggesting a dry up of the central Saharan rivers. Later, marked short-lived spikes of clay and opal may indicate ongoing ephemeral pulses of fluvial runoff linked to peak interglacial stages. Aridification of the south Sahara and Sahel increased in several steps: at 4.6, 4.3 and especially at 4.0, 3.6 and 2.1 Ma, and again, at 0.8 Ma. The late Miocene and earliest Pliocene were humid. Central and north Sahara climate appears to be linked to the glaciation history of the Northern Hemisphere. Spatial distribution of quartz accumulation suggests that the dust outbreaks linked to the Intertropical Convergence Zone during summer did not shift in latitude back to 4.0 Ma, at least. Short-term variations of dust output over the last 0.5 my followed orbital scale pulses with a strong precessional signal, showing a link of Sahelian humidity changes to the variation of sea-surface temperature and evaporation in the tropical Atlantic.

Description: Growth line analysis of diagenetically altered scleractinians is only possible if carbonate diagenesis has followed the pathway of aragonite leaching and coeval formation of low magnesium calcite. All other possibilities of aragonite transformation into calcite exclude the preservation of this growth line banding. Examples of these diagenetic patterns are found in the Pleistocene of Barbados.

Description: Clay- and silt-size mineral assemblages are described from eight piston cores from the fiords and shelf on the western margin of Baffin Bay, Arctic Canada. Radiocarbon dates indicate that all the cores extend back in time to the last local glacial/interglacial transition (i.e. 8–10 ka); four extend back to between 10 and 12 ka, and HU77-021-156, located on the Southeast Baffin Island shelf, includes the entire late Foxe glacial stage. Silt- and clay-size particles constitute ca 40 and 55%, respectively, by weight of the bulk sediment. The clay-size fraction is dominated by mica; feldspars and quartz are the main constituents of the silt fraction. The fiord sediments are mainly composed of local mineralogies, but on the shelf, and at times in the fiords, exotic mineral species occur. The most important of these are detrital carbonates, derived from erosion of the Paleozoic basins in Arctic Canada and/or northwest Greenland. Both calcite and dolomite occur; calcite is the major carbonate mineral in the “southern” cores, whereas dolomite is the most abundant in cores north of 66°N. Higher inputs of carbonate species occur during regional deglaciation, 7–10 ka, and during the last 5 ka (probably reflecting increased iceberg production from northwest Greenland). Thus variations in the precentages of the carbonate minerals indicate significant shifts in Late Quaternary glacial-sediment source areas and oceanographic regimes.

Description: Changes in composition of modern benthic ostracod faunas across the continental margin of southwestern Africa occur at boundaries between and within major water masses: a Mixed Layer-Antarctic Intermediate Water (AAIW) boundary at 200 m, an AAIW salinity minimum zone at 650 m, an AAIW bathyal thermocline at 1000 m, and the AAIW/North Atlantic Deep Water (NADW) boundary at 1500 m. In addition, two population changes occur within the NADW at 1.8–2.0 km and 2.0–3.0 km. The Antarctic Bottom Water assemblage is sparse and poorly preserved.

Description: Der Himalaya ist als höchstes Gebirgssystem unserer Erde wesentlich älter als vermutet. Bisher gingen Geowissenschaftler davon aus, daß der Aufstieg des Himalaya vor 10 Millionen Jahren begann. Jetzt konnte jedoch nachgewiesen werden, daß die Gebirgsbildung mindestens 10 Millionen Jahre früher begonnen hat, der Himalaya also doppelt so alt ist wie bisher angenommen. Zu diesem Ergebnis kamen Meeresgeologen im Indischen Ozean an Bord des Bohrschiffes Joides Resolution während des Fahrtabschnittes (Leg) 116 des internationalen Tiefseebohrprogrammes ODP (Ocean Drilling Program) im Sommer 1987. Grundlage der Untersuchungen waren 3 Bohrungen 800 km südlich von Sri Lanka in 4 700 m Wassertiefe (Abbildung 1). An der 43tägigen Expedition nahmen 25 Wissenschaftler (siehe Tabelle 1) und 18 Techniker aus Großbritannien, Frankreich, Indien, Italien, Japan, Kanada, Sri Lanka, USA und der Bundesrepublik Deutschland teil.

Description: Li/Ca ratios in modern brachiopod shells generally correlate inversely with growth temperature, ranging from ∼20 µmol/mol at 30°C to ∼50 µmol/mol at 0°C with no apparent interspecific offsets. Causes of the temperature effect on Li/Ca ratios are not yet understood. Cenozoic brachiopod Li/Ca ratios average ∼30 µmol/mol, similar to the average observed in modern brachiopods. Relatively constant Li/Ca ratios for Eocene to Pleistocene nonluminescent brachiopod shells, consistent with previous observations of Cenozoic planktonic foraminifera, support the conclusion of little variation in Cenozoic seawater Li/Ca. Nonluminescent portions of Permian and Carboniferous brachiopods have Li/Ca ratios substantially lower (generally 〈10 µmol/mol) than modern, Cenozoic, or Devonian samples. Mass balance considerations, constrained by δ18O of brachiopods, suggest that low Li concentrations in Permo-Carboniferous seawater could be the result of a lower flux of dissolved Li from the continents and/or a higher flux of Li from seawater to clastic marine sediments. Nonluminescent Devonian brachiopods from a single hand specimen have Li/Ca ratios around 70% of the modern average. These Li/Ca ratios can be explained by either somewhat higher temperature with constant seawater Li/Ca, somewhat lower seawater Li/Ca at constant temperature, or a combination of slightly elevated temperature and slightly lower seawater Li/Ca.

Description: Ectothiorhodospira mobilis is a halophilic phototrophic bacterium that has been isolated from soda lakes containing high concentrations of sulphate, chloride and carbonates. It utilizes reduced sulphur compounds as photosynthetic electron donors and oxidizes them to sulphate, but can also grow photoheterotrophically with sulphate as sole sulphur source. The requirements for, and the cytoplasmic concentrations of, sulphate and chloride have been determined. High concentrations of sulphate are neither required for nor inhibit growth. Although chloride is by far the dominant anion of the environment, growth of E. mobilis occurs in the absence of added chloride. Sodium chloride can be replaced by sodium sulphate and sodium carbonate. Chloride is excluded from the cytoplasm with decreasing ratios of cytoplasmic/external chloride at increasing external chloride concentrations (under iso-osmotic conditions).

Description: Eocene to Holocene sediments from Ocean Drilling Program (ODP) Site 647 (Leg 105) in the southern Labrador Sea, approximately 200 km south of the Gloria Drift deposits, were investigated for their biogenic silica composition. Three sections of different diagenetic alteration products of primary siliceous components could be distinguished: (1) opal-A was recorded in the Miocene and the early Oligocene time intervals with strongly corroded siliceous skeletons in the Miocene and mostly well preserved biogenic opal in the early Oligocene; (2) opal-CT precipitation occurs between 250-440 meters below seafloor (mbsf) (earliest Oligocene to late Eocene); (3) between 620-650 mbsf (early/middle Eocene), biogenic opal was transformed to clay minerals by authigenesis of smectites. Using accumulation rates of biogenic opal, paleoproductivity was estimated for the early Oligocene to late Eocene interval. A maximum productivity of biogenic silica probably occurred between 35.5 and 34.5 Ma (early Oligocene). No evidence for opal sedimentation during most of middle Eocene was found. However, at the early/middle Eocene boundary (around 52 Ma), increased opal fluxes were documented by diagenetic alteration products of siliceous skeletons.

Description: Turrialba volcano, the southeasternmost volcano in the Central American arc, is constructed of medium to high-K calcalkaline basalts, andesites, and dacites, plus rare basalts with unusually high Nb concentrations. The compositions of these high-Nb basalts are more similar to those of intraplate basalts than they are to typical calcalkaline or arc-tholeiitic basalts. The association of calcalkaline and high-Nb basalts is rare in arc front volcanoes, seemingly being restricted to volcanoes that overlie Oligocene or younger subducting crust or that overlie the edges of subducting plates. The calcalkaline and high-Nb basalts at Turrialba have generally similar major element, trace element, and isotopic compositions but differ significantly in their Ba/La and La/Nb ratios. The geochemical similarities imply that they were derived from similar ocean island basalt sources. Their geochemical differences suggest that residual rutile stabilized by a large ion lithophile element bearing slab-derived fluid was present during calcalkaline basalt genesis but not during high-Nb basalt genesis. To explain the stability of rutile in a calcalkaline melt with a relatively low TiO2 concentration, we use a model that involves two stages of melting for both basalt types. Silica saturated high degree melts with mid-ocean ridge basalt like incompatible element concentrations generated by upwelling mantle are used as mixing end-members for both the calcalkaline and the high-Nb basalts. The calcalkaline basalts represent mixtures of the high-degree melts and oxidized small-degree melts generated by amphibole breakdown in mantle overlying the subducting slab. This small-degree melt has high incompatible element concentrations and is saturated in rutile. Arc-related lamprophyric rocks have compositions that are appropriate for these small-degree melts. High-Nb basalts are mixtures of the high-degree melts and more reduced small-degree melts that are undersaturated in rutile. These reduced melts may migrate around or through the subducting slab into the wedge to become involved in arc magma genesis.

Description: Based on sediment physical property data from DSDP/ ODP Legs 78A and 110 (Barbados Ridge Complex), a simple palinspastic reconstruction scheme was employed to study porosity changes during accretion. Undoing the compactional effects caused by imbricate stacking of wedge slices, a synthetic pre-accretion porosity depth profile was developed, which bears strong resemblence to a characteristic profile from a reference drillhole in front of the Barbados accretionary complex. Differences between synthetic and reference profile are interpreted in terms of a semiquantitative estimate of the relative impact of the horizontal stress component on gravitational compaction in accretionary wedge environments. An exponential relationship between depth and porosity divergence for distinct lithologic units is evident. The defined relationship facilitates the analysis of deformational behavior of accreted sediments in general.

Description: Based on available nonexclusive seismic data, a preliminary model has been developed for salt deformation on the deep margin of the central Gulf of Mexico basin. In this model, the Tertiary clastic wedge prograded to the basinward limit of original Jurassic salt by the middle Miocene. As the salt and overburden thinned basinward, lateral flow, combined with a strong component of downward force exerted by subsiding voluminous middle Miocene loading, caused the basinward limit of the Louann Salt to effectively shear off. Deposition of the upper Miocene and Pliocene sediments was confined primarily shoreward of an incipient salt swell, but Pleistocene sediments were eventually able to breach the barrier.

Description: At ODP Site 661 from the continental margin of Northwest Africa, authigenic clinoptilolites were investigated in detail. Based on chemical data, crystal size and shape and their intergrowth with associated mineral phases, two types of clinoptilolite (type A and B) occur representing different diagenetic conditions under which the formation of zeolites took place. Clinoptilolite type A was found in a sediment section comprises numerous hiatuses and stratigraphically condensed sediments and could have been formed during early diagenesis. In contrast, clinoptilolite type B was precipitated in Campanian sediments during later diagenesis, after the transformation from opal-A to opal-CT had taken place. At Site 661, the silica source for the authigenesis of both clinoptilolite types is biogenic opal. Volcanic ash material occurs, but in low amounts and thus is not a prerequisite for the formation of clinoptilolite at Site 661.