first_imgThe fauna reported here was obtained from the Legoupil Formation in the north-western part of the Antarctic Peninsula (Fig. 1), which has been assigned a Cretaceous age on the basis of radiometric data1,2. Among the first collection of poorly preserved fossils from this formation were two bivalves tentatively referred to the Cretaceous genus Platopis, an identification which substantiated the radiometric evidence. The study of a more recent collection, by members of the British Antarctic Survey, shows, however, that the bivalves have strong Triassic affinities and, since there is no reason to suspect that they are derived, indicates that the Legoupil Formation is of the same age.last_img read more

first_imgCold environments impose several ecological and physiological constraints upon arthropods, including reduction of metabolic rate, locomotory activity, and feeding. These result in slow growth rates and extended life cycles. Additionally, the probability of freezing is accentuated at subzero temperatures. Using data for Antarctic mites, the interplay of such constraints is examined, and the resultant ecophysiological adaptations outlined for a common oribatid mite (Alaskozetes antarcticus) of the maritime Antarctic. The synthesis suggests that its survival strategy is comprised of two components. First, the utilization of above-zero temperatures during the short austral summer to maximize growth and production, and thereby reproduce. These processes are aided by an elevation of its standard metabolic rate, commonly termed cold adaptation. Second, the tolerance of freezing temperatures by supercooling of all its postovum life stages throughout the entire year. Its supercooling potential is enhanced by the presence of glycerol and other polyols in the body fluids, the production of which is mediated by environmental temperature and desiccation at low relative humidities. Thus this species, in common perhaps with many other freezing susceptible arthropods, has ensured its survival in southern polar habitats by the evolution of a bipartite adaptational strategy.last_img read more

first_imgThe terrestrial environment of Signy Island, South Orkney Islands, maritime Antarctic, is undergoing rapid and possibly irreversible change caused by a natural biological agent. During the past decade there has been a dramatic increase in the number of Antarctic fur seals Arctocephalus gazella coming ashore on the island during the short summers. It is not known whether significant numbers of seals were present on the island prior to the initiation of commercial hunting in the early 1820s. The impact that the continuing increase of these seals had made on the island’s terrestrial and freshwater environments has been sudden and locally devastating. The fragile cryptogam-dominated vegetation has suffered physical damage from which it may be impossible to recover. These seals are also frequenting several of the island’s freshwater lakes which are becoming increasingly eutrophic. The long-term implications of this impact are causing serious concern for the future of the lowland terrestrial and freshwater ecosystems on Signy Island if the fur seal population continues to increase.last_img read more

first_imgA 181 m long ice core was drilled at 79°36′51″ S, 45°43′28″ W, near the summit of Berkner Island, Antarctica (886 m a.s.l.). Berkner Island is located between the Filchner and Ronne Ice Shelves, and the ice near the summit shows little lateral flow. The density of the ice core was measured every 3 mm along its length, using attenuation of a gamma-ray beam, which gave an absolute accuracy of 2%. As expected, there is a general density increase with depth, the maximum densities of > 900 kg m−3 being reached just above 100 m depth. Comparison with the electrical conductivity method (ECM) shows density variations with the same wavelength as the annual signals, which can be seen in the ECM log (higher acidity during summer). In the shallowest part of the core, the density of winter layers is higher than that of summer layers, a relationship which is reversed at greater depth. We assume that the densification rates for the two types of firn are different. Similar density phenomena were observed on ice cores from Greenland, showing that such phenomena are not a local effect.last_img read more

first_imgCirrate octopods are conspicuous members of the benthopelagic and bathypelagic communities and include some of the largest invertebrates of the deep-sea. Although they have often been considered to be rare members of deep-sea communities, recent trawlinghas shown that the relative abundance of some cirrates, especially opisthoteuthids, may be locally or regionally high (e.g., Boyle et al., 1998). Cirrates also are presumed to be primitive, morphologically similar to ancestral octopods (Young et al., 1998), althoughrecent observations indicate unexpected adaptations such as bioluminescence (Johnsen et al., 1999) and possibly diverse feeding modes (Vecchione and Young, 1997). Therefore, knowledge of cirrates may contribute substantially to understanding cephalopod evolution as well as deep-sea biology and ecology. However, because they are fragile, the condition of specimens collected up until the past decade generally has been very poor,and our knowledge of the group is rudimentary. New methods, such as videotapes recorded in-situ and gentle collection by submersibles, have allowed substantial new observations and renewed interest in the group.last_img read more

first_imgPetrels are highly mobile seabirds that face many threats and whose conservation is frequently hampered by a lack of understanding of their biology at sea. We used a combination of data from burrow monitoring and geolocation-immersion loggers to study the intra-and inter-seasonal distribution and behaviour of the endangered Chatham Petrel (Pterodroma axillaris), breeding on Rangatira Island, New Zealand. Breeding extended from November to June with a pre-laying exodus of 35 days; an incubation period of 46 days, with up to five incubation shifts; and a chick-rearing period of 87 days, including a desertion period of 10 days. When breeding, Chatham Petrels foraged between the Subtropical Convergence and Subantarctic Fronts, moving 2000-3000 km to the south-east of the Chatham Islands, during the pre-laying exodus and incubation period, but restricting foraging to the south of the Chatham Islands, around the Bollons Seamount, during chick-rearing. Between April and June birds migrated east and north to core non-breeding distributions similar to 1000 km from the coast of Peru and Chile. Birds spent a greater proportion of time resting and nocturnally active during the non-breeding period than when breeding, when birds where active during darkness and daylight. These data contribute to the conservation management of the Chatham Petrel and to conservation initiatives to identity marine protected areas for endangered seabirds on the high seas beyond national jurisdictions.last_img read more

first_imgDespite their pivotal role as primary producers, there is little information as to the diversity and physiology of cyanobacteria in the meltwater ecosystems of polar regions. Thirty cyanobacterial mats from Adelaide Island, Antarctica were investigated using 16S rRNA gene pyrosequencing and automated ribosomal intergenic spacer analysis, and screened for cyanobacterial toxins using molecular and chemical approaches. A total of 274 operational taxonomic units (OTUs) were detected. The richness ranged between 8 and 33 cyanobacterial OTUs per sample, reflecting a high mat diversity. Leptolyngbya and Phormidium (c. 55% and 37% of the OTUs per mat) were dominant. Cyanobacterial community composition was similar between mats, particularly those obtained from closely adjacent locations. The cyanotoxin microcystin was detected in 26 of 27 mats (10–300 ng g-1 organic mass), while cylindrospermopsin, detected for the first time in Antarctica, was present in 21 of 30 mats (2–156 ng g-1 organic mass). The latter was confirmed via liquid chromatography-mass spectrometry and by the presence of the cyrAB and cyrJ genes. This study demonstrates the usefulness of pyrosequencing for characterizing diverse cyanobacterial communities, and confirms that cyanobacteria from extreme environments produce a similar range of cyanotoxins as their temperate counterparts.last_img read more

first_imgThe balance of dayside and nightside reconnection processes within the Earth’s magnetosphere, and its effect on the amount of open magnetic flux threading the ionosphere is well understood in terms of the expanding-contracting polar cap model. However, the nature and character of the consequential fluctuations in the polar cap boundary are poorly understood. By using the poleward auroral luminosity boundary (PALB), as measured by the FUV instrument of the IMAGE spacecraft, as a proxy for the polar cap boundary we have studied the motion of this boundary for more than two years across the complete range of magnetic local time. Our results show that the dayside PALB dynamics are broadly self-similar on timescales of 12 minutes to 6 hours and appear to be monofractal. Similarity with the characteristics of solar wind and interplanetary magnetic field (IMF) variability suggest that this dayside monofractal behaviour is predominantly inherited from the solar wind via the reconnection process. The nightside PALB dynamics exhibit scale-free behaviour at intermediate timescales (12-90 minutes) and appear to be multifractal. We propose that this character is a result of the intermittent multifractal structure of magnetotail reconnection.last_img read more

first_imgSeabirds show remarkable variability in migration strategies among individuals and populations. In this study, we analysed 47 migrations of 28 brown skuas Catharacta antarctica lonnbergi breeding on King George Island in the Maritime Antarctic. Brown skuas from this population used a large area during the non-breeding period north of 55°S, including parts of the Patagonian Shelf, Argentine Basin and South Brazil Shelf, areas which are characterised by high levels of marine productivity. However, individual birds utilised only a subset of these areas, adopting 1 of 4 distinct migration strategies to which they were highly faithful between years, and showed high repeatability in departure and arrival dates at the breeding ground. Although they spent the majority of the non-breeding season within a particular region, almost all individuals used the same area in the late winter, exploiting its seasonal peak in productivity. Overall, these results indicate consistent individual variation in migration strategies that may reflect a combination of genetic control and individual experience, but with considerable flexibility to shift distribution in response to prevailing environmental conditions.last_img read more

first_imgThe study of systematics in wide-ranging seabirds can be challenging due to the vast geographic scales involved, as well as the possible discordance between molecular, morphological and behavioral data. In the Southern Ocean, macaroni penguins (Eudyptes chrysolophus) are distributed over a circumpolar range including populations in Antarctic and sub-Antarctic areas. Macquarie Island, in its relative isolation, is home to a closely related endemic taxon — the royal penguin (Eudyptes schlegeli), which is distinguishable from E. chrysolophus mainly by facial coloration. Although these sister taxa are widely accepted as representing distinct species based on morphological grounds, the extent of their genome-wide differentiation remains uncertain. In this study, we use genome-wide Single Nucleotide Polymorphisms to test genetic differentiation between these geographically isolated taxa and evaluate the main drivers of population structure among breeding colonies of macaroni/royal penguins. Genetic similarity observed between macaroni and royal penguins suggests they constitute a single evolutionary unit. Nevertheless, royal penguins exhibited a tendency to cluster only with macaroni individuals from Kerguelen Island, suggesting that dispersal occurs mainly between these neighboring colonies. A stepping stone model of differentiation of macaroni/royal populations was further supported by a strong pattern of isolation by distance detected across its whole distribution range, possibly driven by large geographic distances between colonies as well as natal philopatry. However, we also detected intraspecific genomic differentiation between Antarctic and sub-Antarctic populations of macaroni penguins, highlighting the role of environmental factors together with geographic distance in the processes of genetic differentiation between Antarctic and sub-Antarctic waters.last_img read more