Observations by the Dynamics Explorer 1 satellite provide validation of the theory that terrestrial myriametric radiation is produced by the linear conversion of electrostatic upper hybrid waves to electromagnetic radiation via a radio window. This theory predicts that the myriametric radiation is beamed relative to the magnetic field lines.
A mixture of tiletamine and zolazepam at a combined dose of 1 mg/kg was a reliable and safe agent for immobilising wild grey seals (Halichoerus grypus) and southern elephant seals (Mirouga leonina). The agent had a number of advantages over all the other agents used previously.
Newly formed bottom water (θ ≤ −0.7°C) in the northern Weddell Sea flows E or NE at speeds up to 10–15 cm/s, with velocity decreasing towards the centre of the Weddell Gyre (preliminary results from long-term current meter moorings). Upper Quaternary sediments from this area contain a fine-grained terrigenous component (from the nepheloid layer) plus biogenic silica (mostly diatoms) with a small amount of ice-rafted debris. In cores from between 61° and 66°S and from 3300 m to 4700 m water-depth, the proportion of biogenic silica increases northwards (corresponding to increasing seasonal extent of open water vs sea-ice cover), and the proportion of silt and well-sorted fine sand in surface sediments increases with average current velocity. Downcore, diatom-rich and diatom-poor sediments alternate on a scale of 1–3 m, and intervals with more diatoms contain a higher proportion of silt to clay. Preliminary stratigraphy suggests the cyclicity in composition and texture is related to glacial-interglacial cyclicity. During warm periods (indirectly correlated with isotope stages 1, 3, 5 etc.) biogenic silica production takes place during several months of each year, and silt and fine sand are transported by bottom currents. During glacial periods with greater sea-ice cover than at present, biogenic productivity was suppressed and no silica was preserved in the sediments: in addition, a lower proportion of terrigenous silt implies that bottom currents were weaker. At sites with a present-day average velocity of 10 cm/s, a Last Glacial Maximum average velocity of 1 cm/s or less is inferred from grain-size measurements.
The site of ice nucleation in the freeze-tolerant, sub-Antarctic beetleHydromedion sparsutumhas been investigated. Ice+bacteria, active at above −2.0°C, were isolated from the guts of beetles and identified as a fluorescentPseudomonasspecies. Other possible sites of nucleation, including the hemolymph, were examined but had a lower activity. Ice+bacteria were isolated from mixed populations, isolated from the guts of adult beetles, and grown on nutrient agar plates and in nutrient broth. Nucleation activity of the broth culture peaked after only 2 days although the number of live cells continued to increase until day 6. These cultures were used to determine the maximum nucleation activity of a bacterial suspension in sterile distilled water (−3.4°C) and the dilution factor required to cause a 50% reduction in activity (104). The original bacterial suspension had an absorbance of 0.5 measured at 660 nm and contained 6 × 1011bacteria per milliliter. From this it is estimated that only 1 in 106bacteria possessed the highest levels of ice-nucleating activity. Other insect species, including Perimylops antarcticus,which are found in habitats similar to that ofH. sparsutum,were examined for the presence of ice+bacteria. All contained ice-nucleating bacteria in their guts but with a lower level of activity than in H. sparsutum.
A new species of the synallactid sea cucumber genus Pseudostichopus is described, P. aemaulatus sp. nov., based on genetic (DNA sequences of the mitochondrial gene Cytochrome Oxidase I [COI] gene) and morphological characters. A comparative molecular study with two other species of the same genus (P villosus and P. mollis) and from a different: Family (Isostichopus fuscus) was carried out in order to clarify its taxonomic identity. The nucleotide distance between P. aemulatus sp. nov. and P. villosus and P. mollis is sufficient to support distinct species status. The estimated difference in the number of amino acids, coded for by a partially sequenced COI gene, within the species of the family Synallactidae ranged from 4 to 18. The phylogenetic analysis clearly supports separate species status of these sympatric morphotypes, as indicated by the morphological analysis.
1. Lakes and ponds in the Larsemann Hills and Bolingen Islands (East-Antarctica) were characterised by cyanobacteria-dominated, benthic microbial mats. A 56-lake dataset representing the limnological diversity among the more than 150 lakes and ponds in the region was developed to identify and quantify the abiotic conditions associated with cyanobacterial and diatom communities. 2. Limnological diversity in the lakes of the Larsemann Hills and Bolingen Islands was associated primarily with conductivity and conductivity-related variables (concentrations of major ions and alkalinity), and variation in lake morphometry (depth, catchment and lake area). Low concentrations of pigments, phosphate, nitrogen, DOC and TOC in the water column of most lakes suggest extremely low water column productivity and hence high water clarity, and may thus contribute to the ecological success of benthic microbial mats in this region. 3. Benthic communities consisted of prostrate and sometimes finely laminated mats, flake mats, epilithic and interstitial microbial mats. Mat physiognomy and carotenoid/chlorophyll ratios were strongly related to lake depth, but not to conductivity. 4. Morphological-taxonomic analyses revealed the presence of 26 diatom morphospecies and 33 cyanobacterial morphotypes. Mats of shallow lakes (interstitial and flake mats) and those of deeper lakes (prostrate mats) were characterised by different dominant cyanobacterial morphotypes. No relationship was found between the distribution of these morphotypes and conductivity. In contrast, variation in diatom species composition was strongly related to both lake depth and conductivity. Shallow ponds were mainly characterised by aerial diatoms (e.g. Diadesmis cf. perpusilla and Hantzschia spp.). In deep lakes, communities were dominated by Psammothidium abundans and Stauroforma inermis. Lakes with conductivities higher than +/-1.5 mS cm(-1) became susceptible to freezing out of salts and hence pronounced conductivity fluctuations. In these lakes P. abundans and S. inermis were replaced by Amphora veneta. Stomatocysts were important only in shallow freshwater lakes. 5. Ice cover influenced microbial mat structure and composition both directly by physical disturbance in shallow lakes and by influencing light availability in deeper lakes, as well as indirectly by generating conductivity increases and promoting the development of seasonal anoxia. 6. The relationships between diatom species composition and conductivity, and diatom species composition and depth, were statistically significant. Transfer functions based on these data can therefore be used in paleolimnological reconstruction to infer changes in the precipitation-evaporation balance in continental Antarctic lakes.
Dust can affect the radiative balance of the atmosphere by absorbing or reflecting incoming solar radiation(1); it can also be a source of micronutrients, such as iron, to the ocean(2). It has been suggested that production, transport and deposition of dust is influenced by climatic changes on glacial-interglacial timescales(3-6). Here we present a high- resolution record of aeolian dust from the EPICA Dome C ice core in East Antarctica, which provides an undisturbed climate sequence over the past eight climatic cycles(7,8). We find that there is a significant correlation between dust flux and temperature records during glacial periods that is absent during interglacial periods. Our data suggest that dust flux is increasingly correlated with Antarctic temperature as the climate becomes colder. We interpret this as progressive coupling of the climates of Antarctic and lower latitudes. Limited changes in glacial-interglacial atmospheric transport time(4,9,10) suggest that the sources and lifetime of dust are the main factors controlling the high glacial dust input. We propose that the observed similar to 25-fold increase in glacial dust flux over all eight glacial periods can be attributed to a strengthening of South American dust sources, together with a longer lifetime for atmospheric dust particles in the upper troposphere resulting from a reduced hydrological cycle during the ice ages.
Under the Antarctic Treaty System, environmental monitoring is a legal obligation for signatory nations and an essential tool for managers attempting to minimize local human impacts, but is it given the importance it merits? Antarctica is a vast frozen continent with an area around 1.5 times that of Europe (14 000 000 km2), but the majority of its terrestrial life is found on multiple outcrops or ‘islands’ of ice-free coastal ground, with a combined area of ~6000 km2, equivalent to four times that of Greater London (Tin et al 2009). The biological communities of these ice-free terrestrial habitats are dominated by a small number of biological groups, primarily mosses, lichens, microinvertebrates and microorganisms. They include many endemic species, while birds and marine mammals use coastal areas as breeding sites (Chown and Convey 2007).
Relationships between events in one period of the annual cycle and behaviour in subsequent seasons are key determinants of individual life histories and population dynamics. However, studying such associations is challenging, given the difficulties in following individuals across seasons, particularly in migratory species. Relationships between breeding performance and subsequent winter ecology are particularly poorly understood, yet are likely to be profoundly important because of the costs of reproduction. Using geolocation technology, we show that black-legged kittiwakes that experienced breeding failure left their colony in southeast Scotland earlier than successful breeders. Moreover, a greater proportion of unsuccessful breeders (94% versus 53% successful) travelled over 3000 km to the West Atlantic, whereas fewer visited the East Atlantic (31% versus 80% successful), less than 1000 km from the colony. The two groups did not differ in the timing of return to the colony the following spring. However, 58 per cent of males made a previously undescribed long-distance pre-breeding movement to the central Atlantic. Our results demonstrate important links between reproductive performance and winter distribution, with significant implications for population dynamics. Furthermore, macro-scale segregation associated with breeding outcome is relevant to defining important wintering areas, in particular among declining species experiencing increasingly regular breeding failure.
The spatial distribution of turbulent dissipation rates and internal wave field characteristics is analysed across two contrasting regimes of the Antarctic Circumpolar Current (ACC), using microstructure and finestructure data collected as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). Mid-depth turbulent dissipation rates are found to increase from O (1×10-10 W kg-1) in the Southeast Pacific to O (1×10-9 W kg-1) in the Scotia Sea, typically reaching 3×10-9 W kg-1 within a kilometre of the seabed. Enhanced levels of turbulent mixing are associated with strong near-bottom flows, rough topography, and regions where the internal wave field is found to have enhanced energy, a less-inertial frequency content and a dominance of upward-propagating energy. These results strongly suggest that bottom-generated internal waves play a major role in determining the spatial distribution of turbulent dissipation in the ACC. The energy flux associated with the bottom internal wave generation process is calculated using wave radiation theory, and found to vary between 0.8 mWm-2 in the Southeast Pacific and 14 m W m-2 in the Scotia Sea. Typically, 10-30% of this energy is found to dissipate within 1 km of the seabed. Comparison between turbulent dissipation rates inferred from finestructure parameterizations and microstructure-derived estimates suggests a significant departure from wave-wave interaction physics in the near-field of wave generation sites.