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.