Finger numbness and temperature in Antarctica

first_imgA group of new arrivals in Antarctica and a group staying a second consecutive year were observed over a period of one year. Differences of cold acclimatization in finger sensitivity was demonstrated which were lost within 6 weeks. There was no difference in resting finger temperature between the groups, but there was a significant fall in temperature over the year. It was concluded that some forms of acclimatization to cold occur only after a greater degree of cold stress than do others. Second year men showed the greater immunity to frostbite under the experimental conditions, but this was not proved statistically. The addition of drift snow to the ‘cold’ wind doubled the numbness induced in the finger. Under ‘very cold’ conditions drift increased finger numbness over six times. Provided sufficient time is spent outdoors, the outdoor temperature is the more important for cold acclimatization, regardless of comfortable indoor temperatures.last_img read more

Comparative respirometry of peat decomposition on a latitudinal transect in the maritime Antarctic

first_imgThe hypothesis that moss peat respiration in the maritime Antarctic was dependent more on edaphic conditions, substrate quality and microflora than latitude was broadly supported by studies on a 14° transect in 1980–81. Oxygen-uptake and CO2-release of samples from Polytrichum and Drepanocladus communities at five locations were compared by ANOVA. Regression analysis showed moisture and temperature to be prime regulators. A strong but unquantifiable influence of substrate quality was inferred. The influence of microbial biomass was blurred by variation. the absence in Polytrichum of significant multiple regressions of respiration with moisture and temperature implied stable respiration during a summer period of relatively invariable moisture, pH, Eh and potential substrate availability. Conversely, the occurrence of Drepanocladus in a broader range of moisture conditions yielded a significant regression. When extrapolated to estimate annual C-loss, this was similar to estimates for the 1975–77 seasons at Signy Island which was thereby shown to represent the maritime Antarctic.last_img read more

The physical properties of quartz-micaschist and their application to freeze-thaw weathering studies in the maritime antarctic

first_imgAs part of a study on freeze‐thaw weathering in the maritime Antarctic an investigation was made of the physical properties of the local rock. Tests were made of point‐load compressive strength, Schmidt hammer in situ rock strength, moisture content, indentor resistance and the size range of weathering products. The resulting data were used to consider the form of freeze‐thaw weathering operative in the field and its relationship to laboratory simulations. A distinct difference between ‘massive rock’ and ‘intact rock’ is observed in the field. It is suggested that future studies should generate a greater database pertaining to rock properties as it is an invaluable aid in the study of mechanical weatheringlast_img read more

Age determination of European lobsters (Homarus Gammarus L.) by histological quantification of lipofuscin

first_imgDuring the past decade, quantification of the pigment lipofuscin in the olfactory lobe cell masses (OLCM) has been successfully used for age determination of crustaceans. The aim of the current study was to quantify the amount of lipofuscin in European lobsters (Homarus gammarus L.) of known age and to determine the accuracy of lipofuscin as an age predictor. Lipofuscin was quantified by confocal fluorescence microscopy and image analysis of histological sections. Our results showed that age and OLCM lipofuscin were closely and linearly related (r2 = 0.88). Furthermore, in contrast to earlier studies, age was also closely, but nonlinearly, related to carapace length (r2 = 0.78). Comparison of lipofuscin and carapace length as age predictors nevertheless showed that lipofuscin produced significantly more accurate estimates of age than carapace length. The relatively small difference in the precision of age estimation between lipofuscin and carapace length emphasises the importance of evaluating the relationship between age and carapace length/lipofuscin in studies of populations with variable environmental conditions or demographic processes. It is possible that age, in specific situations, could be satisfactorily predicted on basis of measurements of size.last_img read more

Behavioural flexibility during year-round foraging in macaroni penguins

first_imgPenguins are major consumers in the marine environment. However, like many top predators, very little information exists on their foraging behaviour outside the breeding season. We investigated the foraging behaviour of the macaroni penguin Eudyptes chrysolophus continuously for 2 consecutive years, from the end of December 2001. This allowed us to investigate whether foraging behaviour varied between sexes, years or phases of the annual cycle. Male penguins tended to dive deeper and longer than female penguins, but at a lower frequency, probably as a result of their larger body size. There was little variation in foraging behaviour between the 2 years studied, although neither year included a notable period of low Antarctic krill abundance. Diving behaviour varied substantially within years and general linear models were used to investigate this variability. In summary, all penguins tended to dive deeper, longer and more efficiently during their winter migration than during the summer breeding season. The penguins dived predominantly during daylight hours at all times of the year, but appeared to be more constrained by daylight during the short winter days. Several diving variables including dive duration, dive rate and amount of time spent diving were significantly related to day length and these associations were stronger during winter than summer. The macaroni penguin shows flexibility in its foraging behaviour as it adapts to differing constraints and challenges during its annual cycle.last_img read more

On the occurrence of auroral westward flow channels and substorm phase

first_imgAuroral westward flow channels (AWFCs) are intense, narrow channels of westward drift overlapping the equatorward edge of the auroral oval in the pre-magnetic midnight sector. They are a close relative of the sub-auroral polarisation stream which encompasses polarisation jets, a phenomenon also known as sub-auroral ion drift events. Recent observations made with the Tasman Geospace Environment Radar (TIGER) (147.2°E, 43.4°S Geodetic; 55.0° Geomagnetic) have revealed close associations between the appearance of AWFCs and substorm onset, and their subsequent decay toward the end of recovery phase. In fact, in terms of electric field strength, they are the strongest signatures of substorms in the ionospheric convection (>50 mV m−1). In terms of electric potential difference (>10 kV), they also represent a substantial fraction of the total potential difference generated during substorms. The AWFCs exhibit a diverse range of behaviour, there being no typical event. The radar observations show that radial polarisation fields sometimes oscillate towards and away from the Earth, and bifurcate, within regions of closed flux in the magnetotail throughout substorm evolution. We have identified every AWFC observed by TIGER during the first year of operation, 2000. Simple statistical arguments imply that one, if not more, AWFC probably occurs during every substorm. AWFCs are a fundamental aspect of substorm evolution.last_img read more

Acquisition and assimilation of nitrogen as peptide-bound and D-enantiomers of amino acids by wheat

first_imgNitrogen is a key regulator of primary productivity in many terrestrial ecosystems. Historically, only inorganic N (NH4+ and NO3-) and L-amino acids have been considered to be important to the N nutrition of terrestrial plants. However, amino acids are also present in soil as small peptides and in D-enantiomeric form. We compared the uptake and assimilation of N as free amino acid and short homopeptide in both L- and D-enantiomeric forms. Sterile roots of wheat (Triticum aestivum L.) plants were exposed to solutions containing either 14C-labelled L-alanine, D-alanine, L-trialanine or D-trialanine at a concentration likely to be found in soil solution (10 µM). Over 5 h, plants took up L-alanine, D-alanine and L-trialanine at rates of 0.9±0.3, 0.3±0.06 and 0.3±0.04 µmol g−1 root DW h−1, respectively. The rate of N uptake as L-trialanine was the same as that as L-alanine. Plants lost ca.60% of amino acid C taken up in respiration, regardless of the enantiomeric form, but more (ca.80%) of the L-trialanine C than amino acid C was respired. When supplied in solutions of mixed N form, N uptake as D-alanine was ca.5-fold faster than as NO3-, but slower than as L-alanine, L-trialanine and NH4+. Plants showed a limited capacity to take up D-trialanine (0.04±0.03 µmol g−1 root DW h−1), but did not appear to be able to metabolise it. We conclude that wheat is able to utilise L-peptide and D-amino acid N at rates comparable to those of N forms of acknowledged importance, namely L-amino acids and inorganic N. This is true even when solutes are supplied at realistic soil concentrations and when other forms of N are available. We suggest that it may be necessary to reconsider which forms of soil N are important in the terrestrial N cycle.last_img read more

Iron localization in Acarospora colonizing schist on Signy Island

first_imgA small, inconspicuous lichen, Acarospora cf. badiofusca, was discovered colonizing ironstainedquartz mica schists on the lower slope of Manhaul Rock, a recently exposed nunatak on the McLeodGlacier, Signy Island, South Orkney Islands. Thallus colour ranged from rust on exposed rock surfaces topaler orange and green in shaded crevices. This study addressed the hypothesis that colour reflects elementlocalization, and considered substance localization within lichen tissues and responses to stress. Electronmicroprobe analysis of specimens confirmed that Fe is localized principally in the outer rust-coloured partof the cortex, confirming that the colour reflects Fe localization. Oxalates, widely reported as contributingto tolerance mechanisms to environmental stress, were not detected using X-ray diffraction. The upperthallus surface consisted of sub-micron particulate phases containing Fe, Al and O, suggesting mixed oxide/hydroxide phases are present and play a role in photoprotection.last_img read more

Gentlemen first? ‘Broken stick’ modelling reveals sex-related homing decision date in migrating seabirds

first_imgTechnical progress in animal-borne tracking and movement data analysis has facilitated the understanding of the interplay between successive periods in the life cycle of migratory animals. We investigated how sex differences on the constraints of homing may influence migration to breeding areas in crested penguins (genus Eudyptes). We used a novel approach to infer homing decision date, a precise point in time that translates statistically as a change point in the current distance of the animal to its colony (‘broken stick’ modelling approach, R codes provided here). We applied this approach to geolocation tracking data on migration in three Eudyptes species, from three localities in the southern Indian Ocean (five populations). Sex had a subtle and consistent influence on the temporal activity of the 66 animals during their migratory journey. Males began migration to the breeding localities earlier than females, by an average of 9.1 (range: 4.5–13.5) days. This difference was statistically significant in 4 of 5 populations, and occurred among all species, sites and years surveyed. Our study shows an original application of a recent modelling approach to detect change point in movement data. Our results suggest that sex-specific constraints related to breeding in migrating animals may also modify activity schedules well before breeding commences.last_img read more

Spatial and temporal variations in basal melting at Nivlisen ice shelf, East Antarctica, derived from phase-sensitive radars

first_imgThinning rates of ice shelves vary widely around Antarctica, and basal melting is a major component of ice shelf mass loss. In this study, we present records of basal melting at a unique spatial and temporal resolution for East Antarctica, derived from autonomous phase-sensitive radars. These records show spatial and temporal variations of basal melting in 2017 and 2018 at Nivlisen, an ice shelf in central Dronning Maud Land. The annually averaged basal melt rates are in general moderate (∼0.8 m yr−1). Radar profiling of the ice shelf shows variable ice thickness from smooth beds to basal crevasses and channels. The highest basal melt rates (3.9 m yr−1) were observed close to a grounded feature near the ice shelf front. Daily time-varying measurements reveal a seasonal melt signal 4 km from the ice shelf front, at an ice draft of 130 m, where the highest daily basal melt rates occurred in summer (up to 5.6 m yr−1). In comparison with wind, air temperatures, and sea ice cover from reanalysis and satellite data, the seasonality in basal melt rates indicates that summer-warmed ocean surface water was pushed by wind beneath the ice shelf front. We observed a different melt regime 35 km into the ice shelf cavity, at an ice draft of 280 m, with considerably lower basal melt rates (annual average of 0.4 m yr−1) and no seasonality. We conclude that warm deep-ocean water at present has a limited effect on the basal melting of Nivlisen. On the other hand, a warming in surface waters, as a result of diminishing sea ice cover, has the potential to increase basal melting near the ice shelf front. Continuous in situ monitoring of Antarctic ice shelves is needed to understand the complex mechanisms involved in ice shelf–ocean interactions.last_img read more