first_img86Rb uptake was examined in two species of unicellular green algae, Chlamydomonas nivalis isolated from snow, and a cell wall-less mutant of the temperate freshwater Chlamydomonas reinhardii. In C. reinhardii cells grown at 20°C and cooled rapidly to 0°C, 86Rb uptake was abolished. Cells cooled rapidly to −5°C in the absence of ice accumulated 86Rb very rapidly but the time course of this uptake suggested non-selective accumulation through a damaged plasmalemma. Cells grown at 8°C were viable, able to divide and motile; they showed no signs of cold-shock and 86Rb uptake, albeit slow, was measurable at −5°C in the absence of extracellular ice. Cells of C. nivalis grown at 20°C were damaged at sub-zero temperatures although they did show an enhanced 86Rb uptake at 0°C. Cells grown at 5°C were able to accumulate 86Rb from media undercooled to -5°C in the absence of extracellular ice, and again showed enhanced uptake at 0°C. The process of acclimation to low temperature appears to differ in the two species.last_img read more

Read more

first_imgThe diving behaviour of 11 lactating female Antarctic fur seals (Arctocephalus gazella) was recorded for a total of 254 animal-days at sea. Median and maximum dive depths for individuals varied from 8 to 19 m and from 82 to 181 m, respectively, and median and maximum dive durations from 0.75 to 1.17 min and from 2.8–10.0 min, respectively. Theoretical aerobic diving limits were exceeded on  20 m) by having slower rates of descent and ascent and by being confined to the mixed layer at the ocean surface, as judged by records of sea temperature obtained concurrently with records of depth. Dives were grouped into bouts, defined by inflexion points observed in the cumulative probability distribution of surface interval after probit transformation. Bouts (defined by preceding and succeeding surface intervals lasting 13–24 min) occurred within a diel pattern of diving activity, with 74–85% of dives occurring at night. The pattern of diving, in terms of division into bouts, showed greater differences between individual seals than did dive depth and duration. Dives tended to be shorter and shallower later in lactation. Most variation in diving behaviour between individuals was in terms of the proportion of available time spent foraging, bout frequency, and bout duration. The foraging strategy in the Antarctic fur seal is geared to exploiting prey within the surface mixed layer.last_img read more

Read more

first_imgRecently two species of carabid beetle were accidentally introduced onto the sub-Antarctic island of South Georgia. Both species are carnivorous and flightless. One of the species, Trechisibus antarcticus, is locally very abundant and in the process of invading the coastal lowland area, where the endemic herbivorous beetle Hydromedion sparsutum (Perimylopidae) is common. Field samples showed the abundance of the endemic species to be much lower, and its adult body size to be larger, in carabid-infested locations than in carabid-free locations. The sample data allowed us to estimate the growth rate of the H. sparsutum larvae and to reconstruct the most likely life-cycle of both species. A laboratory experiment showed a high mortality for the first three (out of six) larval instars of H. sparsutum in groups which had been subjected to predation by T. antarcticus. The duration of the period during which the larvae are vulnerable to predation was shown in a growth experiment to depend on food type. Quantitative and qualitative aspects of the interaction between the introduced predator and the endemic prey, and conditions which allowed the former to invade are discussedlast_img read more

Read more

first_imgPrevious reviews have recognized patterns of lactation in pinnipeds divided along phylogenetic lines. This study extended previous models of lactation in pinnipeds by explicitly taking into account all the energetic costs to mothers. Based on an analysis of time-energy budgets, the feasible lactation strategy for a species can be shown to depend on body mass. Due to increased metabolic costs of maintenance, species with a large body mass cannot normally sustain lactation by foraging during lactation unless they have access to rich local prey resources. Consequently, large pinnipeds must normally sustain lactation from body reserves. This disadvantage is compensated in large pinnipeds by freedom to forage in support of offspring at greater range whereas small pinnipeds are restricted to foraging within the locality of the pupping colony. In the absence of correlations between major life-history variables and body mass in pinnipeds, the principal patterns of lactation are likely to be different solutions to the trade-off between foraging on a relatively rich prey resource at long range and foraging on a poorer prey resource within a restricted range. Hence phylogeny may be less important than adaptation in the evolution of pinniped lactation.last_img read more

Read more

first_imgAn area of mudwave development has been identified from the northwestern Powell Basin, northern Weddell Sea, Antarctica. The wave-field is located near the base of the continental slope in water depths of 2800–3100 m, along the pathway of Antarctic Bottom Water (AABW) flow from the Weddell Sea. The waves are presently active, migrating up a low angle (0.6°) slope to the northwest. They are typically 20–50 m in amplitude and 2–4 km in wavelength, and cover an area greater than 1000 km2. Swath mapping and high-resolution multi-channel seismic reflection profiling across the area show that the waves developed in association with basin floor channels and strongly current-influenced sediments. Acoustically, the sediments can be divided into three units. The uppermost unit, C, is 0.5 s twt (two-way time) thick with highly continuous, parallel reflectors displaying well-developed waveforms mimicking those at the seabed and, towards the southeast, a basin floor channel. Unit B is up to 0.8 s twt thick, with strong and continuous subhorizontal reflectors. In the mid-upper section of B are developed buried sinusoidal wave-forms and a base of slope depression or `moat’ and a sediment drift which is infilled and buried, the reflector pattern suggesting sediment supply under current control alongslope, interpreted as contouritic sediments. A lower transparent unit, A, is 1–1.5 s twt thick, with occasional reflectors. The original construction of the waves may have been by turbidity currents predominantly supplied from the basin floor channels. Present-day deposition across the waves is maintained by fine-grained sediment as a result of the lateral transfer of distal turbidites from the basin floor channels by bottom currents. It is suggested that the initiation of current-influenced sedimentation was closely linked to the onset of AABW flow during the Early Miocene, following the separation of the South Orkney Microcontinent and the opening of the Powell Basin during the Late Oligocene.last_img

Read more

first_imgErect bryozoans are extremely abundant and diverse in polar waters and individual species may span a wide range in latitude and bathymetry. A number of aspects of lifestyle, including polypide recycling, embryo production, distribution, growth form and epibiosis were compared in three species of erect byozoans. These were collected from two locations; Signy Island (60°S) and Rothera Point, Adelaide Island (68°S) and a variety of depths. All three species were in similar stages of polypide cycling within and between the two sites. In the species Isosecuriflustra rubefacta and Nematoflustra flagellata the rate of brown body production (polypide generations) was slower at Signy Island than at Rothera Point. There was little difference between localities (within species) in the pattern of embryo production and no change in embryo size with depth. Embryos of I. rubefacta, however, were significantly larger at Rothera Point than at Signy Island. The proportion of the community occupied by each species changed with depth, but all three species occurred in shallower water at Rothera Point than at Signy Island. Fouling by epibionts decreased with increasing depth and from Signy Island to Rothera Point, both in terms of per cent cover and number of colonizing taxa. Possible trends with depth and latitude are compared with other studies involving bryozoans. The literature on Antarctic benthic taxa, in general, is also considered to determine whether trends within the Bryozoa are reflected in other groups.last_img read more

Read more

first_imgOcean floor magnetic anomalies show that New Zealand was the last continental fragment to separate from Antarctica during Gondwana break-up, drifting from Marie Byrd Land, West Antarctica, about 84 Ma ago. Prior to continental drift, a voluminous suite of mafic dykes (dated by Ar–Ar laser stepped heating at 107 ± 5 Ma) and anorogenic silicic rocks, including syenites and peralkaline granitoids (95–102 Ma), were emplaced in Marie Byrd Land during a rifting event. The mafic dyke suite includes both high- and low-Ti basalts. Trace element and Sr and Nd isotope compositions of the mafic dykes may be modelled by mixing between tholeiitic OIB (asthenosphere-derived) and alkaline high- to low-Ti alkaline magmas (lithospheric mantle derived). Pb isotopes indicate that the OIB component had a HIMU composition. We suggest that the rift-related magmatism was generated in the vicinity of a mantle plume. The plume helped to control the position of continental separation within the very wide region of continental extension that developed when the Pacific–Phoenix spreading ridge approached the subduction zone. Separation of New Zealand from Antarctica occurred when the Pacific–Phoenix spreading centre propagated into the Antarctic continent. Sea floor spreading in the region of the mantle plume may have caused an outburst of volcanism along the spreading ridge generating an oceanic plateau, now represented by the 10–15 km thick Hikurangi Plateau situated alongside the Chatham Rise, New Zealand. The plateau consists of tholeiitic OIB-MORB basalt, regarded as Cretaceous in age, and similar in composition to the putative tholeiitic end-member in the Marie Byrd Land dykes. The mantle plume is proposed to now underlie the western Ross Sea, centred beneath Mount Erebus, where it was largely responsible for the very voluminous, intraplate, alkaline McMurdo Volcanic Group. A second mantle plume beneath Marie Byrd Land formed the Cenozoic alkaline volcanic province.last_img read more

Read more

first_imgLong-term changes in the physical environment in the Antarctic Peninsula region have significant potential for affecting populations of Antarctic krill (Euphausia superba), a keystone food web species. In order to investigate this, we analysed data on krill-eating predators at South Georgia from 1980 to 2000. Indices of population size and reproductive performance showed declines in all species and an increase in the frequency of years of low reproductive output. Changes in the population structure of krill and its relationship with reproductive performance suggested that the biomass of krill within the largest size class was sufficient to support predator demand in the 1980s but not in the 1990s. We suggest that the effects of underlying changes in the system on the krill population structure have been amplified by predatorinduced mortality, resulting in breeding predators now regularly operating close to the limit of krill availability. Understanding how krill demography is affected by changes in physical environmental factors and by predator consumption and how, in turn, this influences predator performance and survival, is one of the keys to predicting future change in Antarctic marine ecosystems.last_img read more

Read more

first_imgThe Jutulstraumen ice stream in western Dronning Maud Land may conceal a Jurassic continental rift. Delineating the geometry and the magmatic patterns of this inferred glaciated rift in East Antarctica is important to improve our understanding of the regional tectonic and magmatic processes associated with Gondwana break-up. A high-resolution aeromagnetic survey provides new insights over the largely buried tectonic and magmatic patterns of the Jutulstraumen area. Prominent NE-SW oriented aeromagnetic trends are detected over the Jutulstraumen. These trends delineate major inherited structural boundaries, active in Grenvillian (about 1.1 Ga) and Pan-African times (about 500 Ma), which appear to strongly control the location of the later Jurassic rift. The postulated east-ern flank of the rift is marked by a broad positive anomaly over H. U. Sverdrupfjella. Buried Grenvillian age rocks may be the source of the long-wavelength anomaly. However, the higher frequency components correlate with granitoids of late Pan-African age. The inferred western flank of the rift features short-wavelength anoma-lies over the Borgmassivet and Ahlmannryggen areas, indicating a considerably greater extent of mid-Proterozoic tholeiitic sills than apparent in outcrop. In contrast, aeromagnetic signatures suggest that alkaline plutons, which relate to Jurassic rifting, are restricted to outcrop areas along the eastern rift flank. The prominent magnetic low over the Jutulstraumen indicates either a largely amagmatic rift, or perhaps subglacial sediments within the rift basin.last_img read more

Read more

first_imgNo Lepidoptera (butterflies and moths) are known to be residents of South Georgia. This paper presents new records of three lepidopterans on the island. Two, Agrotis ipsilon (Noctuidae) and Plutella xylostella (Yponomeutidae), are well-known migrants. The third, Plodia interpunctella (Pyralidae), is closely associated with human habitation. In the context of regional trends of climate warming P. xylostella may already possess the ecophysiological capacity to permit establishment on South Georgia.last_img read more

Read more