Month: May 2021

Population structure and social organization of southern elephant seals, Mirounga leonina (L.)

first_imgThe population structure and social organization of the Southern Elephant Seal, Mirounga leonina, were studied at South Georgia principally by extensive field census work and determination of age and reproductive history from sections of teeth taken from samples of bulls and cows. The adult males of the South Georgia population were exploited from 1910 to 1964, mainly at the maximum sustainable yield for this population. The present data are compared with similar information obtained from studies at South Georgia in 1951 during the exploitation phase and at Macquarie Island in the 1950’s where sealing ended in 1919 and the population had stabilized. Changes have been noted in the time of bull haul out, number of bulls ashore, cow: bull ratio, harem size and the age of harem bulls. These changes can all be attributed to the ending of exploitation. In contrast, the structure of the cow herd has not changed appreciably in the same period. In addition, differences in growth, body size and population structure still persist between the South Georgia and Macquarie Island populations and it is likely that most of them may reflect differences in food availability at the two locations.last_img read more

Size at sexual maturity of Patagonian toothfish (Dissostichus eleginoides)

first_imgAnalyses of size at sexual maturity were undertaken on samples of Patagonian toothfish (Dissostichus eleginoides) caught in the commercial fishery within Subarea 48.3. The results for 1996 indicate that Lm50 occurs at 78.5 cm total length for male and 98.2 cm for female fish. In 1997 the results for male fish were essentially the same. For female fish there is evidence that in 1997 a significant proportion, 25 to 43%, of sexually mature fish were not coming into spawning condition. This introduces a bias leading to the overestimation Lm50 of calculated by conventional methods. Further analysis allowing for this bias indicates that Lm50 for female fish in 1997 was no different to that for 1996. The implications of this phenomenon are discussed.last_img read more

Age and environment of Miocene-Pliocene glaciomarine deposits, James Ross Island, Antarctica

first_imgKnowledge of the late Miocene-Pliocene climate of West Antarctica, recorded by sedimentary units within the James Ross Island Volcanic Group, is still fragmentary. Late Miocene glacio-marine deposits at the base of the group in eastern James Ross Island (Hobbs Glacier Formation) and Late Pliocene (3 Ma) interglacial strata at its local top on Cockburn Island (Cockburn Island Formation) have been studied extensively, but other Neogene sedimentary rocks on James Ross Island have thus far not been considered in great detail. Here, we document two further occurrences of glaciomarine strata, included in an expanded Hobbs Glacier Formation, which demonstrate the stratigraphic complexity of the James Ross Island Volcanic Group: reworked diamictites intercalated within the volcanic sequence at Fiordo Belen, northern James Ross Island, are dated by Ar-40/Ar-39 and Sr-87/Sr-86 at c. 7 Ma (Late Miocene), but massive diamictites which underlie volcanic rocks near Cape Gage, oil eastern James Ross Island, yielded an Ar-Ar age of < 3.1 Ma (Late Pliocene). These age assignments are confirmed by benthic foraminiferal index species of the genus Ammoelphidiella. The geological setting and Cassididina-dominated foraminiferal biofacies of the rocks at Fiordo Belen suggest deposition in water depths of 150-200 m. The periglacial deposits and waterlain tills at Cape Gage were deposited at shallower depths (< 100 in), as indicated by all abundance of the pectinid bivalve 'Zygochlamys' anderssoni and the epibiotic foram Cibicides lobatulus. Macrofaunal and foraminiferal biofacies of glaciomarine and interglacial deposits share many similarities, which suggests that temperature is not the dominant factor in the distribution of late Neogene Antarctic biota. Approximately 10 m.y. of Miocene-Pliocene climatic record is preserved within the rock sequence of the James Ross Island Volcanic Group. Prevailing glacial conditions were punctuated by interglacial conditions around 3 Ma.last_img read more

Observations of the wavenumber 1 and 2 components of the semi-diurnal tide over Antarctica

first_imgThis paper combines four years of radar wind data from Halley and Scott Base in an attempt to resolve the zonal structure of the semi-diurnal tide over Antarctica and to determine the dominant component as a function of time. If only one odd and one even wavenumber component are present then it is possible to calculate the amplitudes and phases of those using data from two stations that are similar in latitude but separated in longitude, ideally by 180. Assuming that the main components of the semi-diurnal tide at Scott Base and Halley latitudes are wavenumber 1 and 2, as has been suggested by other studies, we are able to determine the seasonal variation of both components. The wavenumber 1 component is often dominant in summer, in winter a mixture of wavenumber 1 and 2 is observed. In addition the longitude at which the maxima of the components coincide was determined and found to vary relatively little. Amplitude variations and the longitudes of maxima coincidence were used to investigate the generation mechanisms of the wavenumber 1 wave. Interaction between planetary waves with wavenumber 1 and the wavenumber 2 semi-diurnal tide was found to be a potential mechanism for the generation of the wavenumber 1 component of the tide, confirming theories and observations discussed in the literature. For periods where this explanation for the generation of the wavenumber 1 tide fails we suggest asymmetric heating through solar particle flux as an additional source.last_img read more

Quasi-biennial oscillation influence on long-period planetarywaves in the Antarctic upper mesosphere

Long-period planetary wave data derived from meteor wind observations recordedover a 12-year period with the SuperDARN radar at Halley, Antarctica, are presentedand compared with the phase of the quasi-biennial oscillation (QBO) throughout theequatorial stratosphere. Enhanced planetary wave activity in the Antarctic uppermesosphere is found during the summer months, when the QBO in the equatorial upperstratosphere is westerly, and during the late winter, when the QBO in the upperstratosphere is easterly. These quasi-biennial enhancements in planetary wave activitycoincide with a reduction in strength, by up to 30%, of the late-winter eastward winds inthe Antarctic upper mesosphere. In addition, when the QBO is in the correct phase forenhanced planetary wave activity in the upper mesosphere above Halley, planetary waveactivity measured in the upper mesosphere of the high-latitude Northern Hemisphere isreduced (and vice versa). These results clearly indicate significant interhemisphericpropagation of planetary waves from the winter to summer hemispheres. Observationalevidence that the stratospheric QBO induces a strong enough QBO in the equatorial uppermesosphere to act as a gate to the interhemispheric propagation of these long-periodwaves is discussed in light of these results. read more

Remote sensing space weather events: Antarctic-Arctic radiation-belt (Dynamic) Deposition-VLF Atmospheric Research Konsortium network

[1] The Antarctic-Arctic Radiation-belt (Dynamic) Deposition-VLF Atmospheric Research Konsortium(AARDDVARK) provides a network of continuous long-range observations of the lower ionosphere in thepolar regions. Our ultimate aim is to develop the network of sensors to detect changes in ionizationlevels from 30–90 km altitude, globally, continuously, and with high time resolution, with the goal ofincreasing the understanding of energy coupling between the Earth’s atmosphere, the Sun, and space. Thisscience area impacts our knowledge of space weather processes, global atmospheric change,communications, and navigation. The joint New Zealand-United Kingdom AARDDVARK is a newextension of a well-established experimental technique, allowing long-range probing of ionization changesat comparatively low altitudes. Most other instruments which can probe the same altitudes are limitedto essentially overhead measurements. At this stage AARDDVARK is essentially unique, as similar systemsare only deployed at a regional level. The AARDDVARK network has contributed to the scientificunderstanding of a growing list of space weather science topics including solar proton events, the descentof NOx into the middle atmosphere, substorms, precipitation of energetic electrons by plasmaspherichiss and electromagnetic ion cyclotron waves, the impact of coronal mass ejections upon the radiationbelts, and relativistic electron microbursts. Future additions to the receiver network will increase thescience potential and provide global coverage of space weather event signatures. read more

Mysterious attendance cycles in Cory’s shearwater, Calonectris diomedea: an exploration of patterns and hypotheses

Several species of seabirds show cyclic patterns of attendance at their nesting colonies. We examined the patterns of variation in the numbers of Cory’s shearwater at three colonies (two oceanic and one located on the continental shelf), including the world’s largest, at Selvagem Grande, Madeira, Portugal and considered several hypotheses concerning their causal mechanisms. At Selvagem Grande, cycles were exceptionally marked and regular, with a periodicity ranging from 7.8 to 11 days, and involved both breeders and nonbreeders. In contrast, variation in numbers was aperiodic at a nearby and much smaller colony (Selvagem Pequena), and also at the colony located off the Portuguese coast (Berlenga Island). We found no relationships between number of birds ashore and environmental variables such as wind direction and speed or lunar cycle. Cycles did not seem to be driven by oscillations in food availability or accessibility, given that they did not correlate with daily chick growth rates (which were acyclic) or diet. Despite their regularity, cycles were slightly out of phase in different sectors of Selvagem Grande, which suggests that social interactions at the colony could act as an entrainment agent for an endogenous rhythm, and so cycles are probably more likely to occur in large and dense colonies. Observations are consistent with the hypothesis that cycles facilitate social interactions by maximizing the probability of encounters at the colony. However, the exact mechanisms through which these remarkable cycles are controlled are still completely unknown, and clearly further research is needed. (C) 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. read more

The significance of cephalopod beaks in marine ecology studies: Can we use beaks for DNA analyses and mercury contamination assessment?

first_imgCephalopod beaks found in the diet of predators have been a major source of scientific information. In this study, we evaluated the usefulness of DNA and contaminants analysis (total mercury — T-Hg) in cephalopod beaks in order to assess their applicability as tools in marine ecology studies. We concluded that, when applying DNA techniques to cephalopod beaks from Antarctic squid species, when using flesh attached to those beaks, it was possible to obtain DNA and to successfully identify cephalopod species; DNA was not found on the beaks themselves. This study also showed that it is possible to obtain information on T-Hg concentrations in beaks: the T-Hg concentrations found in the beaks were 6 to 46 times lower than in the flesh of the same cephalopod species. More research on the relationships of mercury concentrations in cephalopod beaks (and other tissues), intra- and inter-specifically, are needed in the future.last_img read more

Redescription and neotype designation of the Antarctic springtail Folsomotoma octooculata (Collembola: Isotomidae)

first_imgThe growing interest in Antarctic collembolan species has led us to re-evaluate both the morphological and molecular aspects of different species adapted to the extreme Antarctic environment. The genus Folsomotoma includes nine species mainly distributed in Antarctic and subantarctic areas and a few additionally from Australia and South America. We herein designate the neotype of Folsomotoma octooculata (Willem 1901) and redescribe its morphological characters with particular emphasis on the sensory and ordinary chaetotaxy. Furthermore, based on analyses of both our new and previously published morphological data for F. octooculata, we propose a systematic key of the species for the genus.last_img read more