ALBERT

Description: The dissolution rates of spheres of two magnesian olivines, two plagioclases, and quartz in tholeiitic basalt have been determined at three super-liquidus temperatures and one-atmosphere pressure. There are considerable differences in the rates among the minerals, e.g. at 1210°, 12° above the liquidus temperature of the basalt, labradorite dissolves at 86 µm/h. and the magnesian olivines at 9 and 14 µm/h. The rates are not time dependent and this, coupled with the existence of concentration gradients in the composition of quenched melt adjacent to partially dissolved crystals, indicates that the dissolution rates are dictated by a combination of diffusion and convection of components to and from the crystal-liquid interface. Values for the activation enthalpy of dissolution are small for quartz and plagioclase (40–50 kcal mol−1) but large for olivine 73–118 kcal mol−1). Dissolution of plagioclase in rock melts seems to be a much more rapid process than crystal growth, whereas olivines apparently dissolve and grow at similar rates. Crystal dissolution is sufficiently slow that ascending, crystal-bearing magma may become superheated and yet fail to dissolve the crystal fraction before quenching; this may be the reason that olivine phenocrysts are often rounded.

Description: Petrographic, mineralogic, and geochemical data are reported for lavas from two of the major shield volcanoes of the Santorini volcanic complex (Skaros and Micro Profitis Ilias), both of which were active prior to the well-known Minoan eruption with associated caldera collapse. Field work and whole-rock chemical analyses indicate four cycles of eruptive activity within the Skaros sequence and three within the Micro Profitis Ilias (M P1) sequence. SiO2 and LIL-element contents decrease from the base to the top of all cycles except for the uppermost cycle of Skaros. Chemical variations within cycles are interpreted to result from eruption from compositionally and thermally zoned magma chambers. Major oxide data and the results of least-squares, mass balance modeling indicate that fractional crystallization played an important role in the development of the observed chemical variations. However, observed systematic variations in groundmass compositions within each cycle, observed irregular variations in total phenocryst content and the results of density calculations require that generation of the chemical zonation did not involve crystal settling but reflects unstable density stratification, probably resulting from sidewall crystallization. Some of the primitive lavas erupted on Santorini preserve phenocryst and xenocryst evidence for a stage of high-pressure fractional crystallization (involving removal of olivine, clinopyroxene, orthopyroxene, and Cr-spinel). Trace element data combined with petrographic data (i.e. the occurrence of abundant phenocrysts with resorption textures) is taken as evidence that magma mixing was also important in the development of cyclic variations. Most basaltic andesites from Skaros appear to be hybrids derived by mixing of basalt and andesite/dacite. Mineralogic data demonstrate that mixing was also important in the development of zonation in the chambers beneath MPI, but trace element data cannot be explained by combined fractionation and mixing alone. Specifically, incompatible, and compatible element abundances are lower than predicted if fractionation and mixing occurred and it is suggested that the anomalous trace element behaviour of especially LIL elements reflects the simultaneous operation of assimilation, for which there is support from isotopic studies. It is concluded that inter- cyclic chemical variations are explicable in terms of fractionation, mixing and assimilation. The LIL element and highly compatible element concentrations in the most primitive lavas erupted in each cycle of Skaros and MPI increase with time, indicating that mixing became more important with time.

Description: Cephalopod remains were collected from all of 12 dead Emperor penguin chicks [Aptenodytes forsteri (Gray)], from 76% of 29 living adult Emperor penguins, and from 18% of 105 living adult Adelie penguins [Pygoscelis adeliae (Hombron & Jacquinot)] from Adelie Land, Antarctica, in 1982. Of the seven species of squids represented by lower beaks, Psychroteuthis glacialis comprised 88% of the number in both Emperor chicks and Emperor adults and 100% in Adelie adults. From estimates of the weight of squids represented by lower beaks, Gonatus antarcticus and Kondakovia longimana contributed 18 and 14%, respectively, of the weight of squids in the diet of Emperor chicks and 27 and 21%, respectively, in the diet of Emperor adults. The data suggest that Psychroteuthis glacialis probably hatch in July–September and grow steadily for one year, and then spawn and die.

Description: The Pantelleria Rift system is a wide zone of post-Miocene northwest-trending grabens and horsts beneath the Sicily Strait. The central grabens host volcanics of predominantly alkalic composition which are exposed on the islands of Pantelleria and Linosa. On the Maltese Islands, along the northeastern shoulder of the rift, an Oligocene-Miocene carbonate succession exposed above sea level allows structural analysis and determination of shallow crustal stresses within the otherwise largely submarine rift system. An older northeast-trending set of normal faults is probably the expression of an Oligocene-Miocene crustal extension event which produced continental rifts in western Europe and led to passive margin formation in the western Mediterranean. Younger northwest-trending grabens of the Pantelleria Rift system cut the older faults almost at right angles and define a zone of lithospheric stretching between Tunisia and Sicily. The northwest-trending grabens which subsided dramatically since the beginning of Pliocene time appear to be connected by east-trending dextral and, more rarely, north-trending sinistral transforms. Displacement along the transforms is probably in the order of a few kilometres. In-situ stress measurements carried out on the Maltese Islands show maximum horizontal compression (SH) parallel to the rift. This suggests that in general σ1 (vertical) and σ2 (horizontal and parallel to the rift) are of about the same magnitude; both exceed σ3 (Sh) which trends northeasterly. Slight intraplate convergence in a NW-SE direction seems to be more than balanced by extension in a NE-SW direction. Neotectonics of the region possibly reflects an asthenospheric flow pattern which became established during the Messinian salinity crisis. The mechanism of recent intraplate deformation of the Pelagian shelf has relevance for the understanding of more anciently subsided platforms of the Apulian Plate.

Description: The fur seal, Arctocephalus gazella, population at Mossman Peninsula (Laurie Island) was studied from 1985 to 1987. Weekly counts were carried out at a 4 km bachelor haul-out beach from December through June. Maxima of 2 240, 2 787 and 5 196 juvenile and adult males were counted during March of the respective years. Census data indicate an increase in the non-breeding population of 13.5% between 1985–1986 and 46.5% between 1986–1987.

Description: Surveys of the interdial macrofauna and sediment characters of Nigg Bay, Moray Firth, were carried out between 1981 and 1985. Permanent stations were located at the intersections of a half-kilometre grid covering the entire interdial area and sampled for infauna using replicate cores. Estimates were also made of mussel and lugworm densities from quadrats and cast counts respectively. The biomass of selected species that constitute important resources for higher tropic levels were also estimated. The sediment for each station was analysed for median particle diameter and slit content. The infaunal data were analysed by Detrended Correspondence Analysis. This indicated that tida height was the most important factor governing the distribution and abundance of the interdial communities. Sediment characters were only poorly related to distribution patterns. The bay has a rich fauna and is biologically similar to other outer bays of the Moray Firth, which, like Nigg, are important areas for wildfowl and waders. Comparison of survey data from different years indicate that there are natural cycles in some sediment and biological characters of Nigg Bay.

Description: Cephalopod beaks recovered from stomach samples taken from l 4 sea bird species in the southern Benguela region off Southern Africa and from one species at Sub-Antarctic Marion Island, were identified as far as possible, counted and the lower rostral lengths (LRLs) measured. Dorsal mantle lengths (DMLs) and body masses of the cephalopods eaten were estimated. The results of analyses by percentage frequency of occurrence and numerical abundance are discussed with reference to present knowledge of the distribution of cephalopods eaten by sea birds in the areas studied. Division of the cephalopod component of seabird diets into species which float, and species which sink, after death indicates that the birds forage on dead or moribund cephalopods on the surface, rather than catching live bioluminescent cephalopods at night.

Description: In the Antarctic there are large unexploited stocks of cephalopods with high potential commercial value and there are two important fisheries for squid in the cool temperate waters of the Southern Ocean, adjacent to the Antarctic, in the Atlantic and Pacific sectors. Squid fisheries can develop very rapidly, and if this were to happen in the Antarctic before adequate management plans could be established, there would be serious consequences for the squid stocks, and also for the vertebrate predator populations which depend on them. It is especially important to increase our knowledge of the Antarctic cephalopod species, their distribution and role in the food chain, and to understand their life cycles