Descripción: • Background and Aims: Trees with a partial leaf-shedding pattern and other morphological features a priori considered intermediate between those of the deciduous Nothofagus antarctica (G. Forster) Oersted and the evergreen N. dombeyi (Mirb.) Oersted (Nothofagaceae) were found in natural stands. The hybridization between a deciduous and an evergreen species of Nothofagus has not been reported so far in natural communities. • Methods: The putative hybrids and the two presumed parental species were compared using 14 enzyme systems as well as shoot, leaf and reproductive morphology. • Key Results: Six enzyme systems showed good resolution (MDH-B, IDH, SKDH, 6-PGDH, GOT and PGI) and in four of them (PGI, MDH-B, SKDH and 6-PGDH) the putative hybrids showed intermediate zymogram patterns between N. antarctica and N. dombeyi. Both principal coordinates analysis on isozyme data and principal components analysis (PCA) on quantitative morphological traits of shoots and leaves separated both parental species and located the putative hybrids closer to N. antarctica than to N. dombeyi. In the PCA, the number of basal cataphylls and the length:width ratio of leaves were the variables most discriminating among shoots of the three entities. The putative hybrids were intermediate between both species regarding leaf vernation, outline and venation, variation in leaf shape (length/width) with position on the parent shoot and in staminate inflorescence and cupule morphology. For other morphological traits, the putative hybrids resembled one of the parental species or differed from both species (e.g. valve morphology). • Conclusions: Isoenzymatic and morphological data sets support the idea of the hybrid nature (probably F 1 generation) of the semi-deciduous trees found. Nothofagus antarctica and N. dombeyi are probably more closely related than previously assumed. The relevance of pollen type in revealing evolutionary relationships between Nothofagus species is supported, and that of leaf-shedding pattern is rejected. © 2004 Annals of Botany Company.

Descripción: In this communication, the genesis of great anomalous seismic activity registered during austral summer 2003/2004 on Deception Island (Antarctica) is discussed, and related with changes on the chemical composition of fumarolic gases and vent deposits. Here we present a comparative analysis performed to explain this activity. We propose a possible parcial seal of the microfracture system. This effect allows an increase on pressure follow by reopening of microfractures, resulting on a sequence of seismic events and changes on the chemical composition of fumarolic emissions.

Descripción: Retrotapes, new genus, comprises a group of Neoaustral bivalves that appeared in the southern circumpolar regions by the Eocene and have since been confined to the high latitudes of the southern hemisphere. Its presence in the Tertiary strata of Antarctica and southern South America reflects an active faunal interchange between both regions during the Eocene. Retrotapes is here proposed to include to those Recent and Tertiary representatives of the Subfamily Tapetinae (Family Veneridae) from southern South America and Antarctica that had been previously placed in Venus Linné, 1758, Marcia H. and A. Adams, 1857, Eurhomalea Cossmann,1920, Samarangia Dall,1902, and Kalelysia Römer, 1857. The Argentine Tertiary species Retrotapes ninfasiensis, new species, R. fuegoensis, new species, R. striatolamellata (Ihering, 1897) and R. scutata (Ihering, 1907) are here described and illustrated. The Recent Argentine Venus exalbida Chemnitz, 1795 and Venus lenticularis Sowerby, 1835, the Antarctic V. antarctica Sharman and Newton, 1894 and V. newtoni Wilckens, 1911 (Eocene-early Oligocène?, La Meseta Formation), and the Neogene Chilean species V. navidadis Philippi, 1887 and V. colchaguensis Philippi, 1887 are also included in this new genus.

Descripción: The rapid changes that are taking place in the climate of the Antarctic Peninsula are triggering hydrological processes which had been limited or inactive for relatively long periods of time. These processes are evident in ice-free areas on the northern edge of the Antarctic Peninsula, such as Cape Lamb, and lead to intense draining of the surface and groundwater system throughout the brief Antarctic summer. The result is a movement of large amounts of water, sediments and nutrients that would be immobilized in other scenarios. This study proposes a model of the operation of the surface and groundwater system that could be valid for several ice-free areas in the region, based on the interpretation of field observations in Cape Lamb, the most extensive ice-free area on Vega Island. The model proposed is further supported by the interpretation of 56 chemical analyses of samples representing groundwater, active layer water, glacier ice and snowfall. The hydrochemical interpretation is supported primarily by four indicators (pH, electrical conductivity, D/18O ratio and SO4/Cl ratio) which have proven to be the most appropriate hydrochemical variables to differentiate the origin and interaction of the waters in the various sections of the system.

Descripción: Deception Island (South Shetlands, Antarctica) is one of the most active volcanoes in Antarctica, having erupted recently in 1967, 1969 and 1970, damaging scientific stations on the island. It is also seismically very active. The island has attracted the attention of many researchers as it constitutes an undisturbed natural laboratory to study seismo-volcanic events and how they affect landscape modelling and evolution. One of the most remarkable geological and geomorphological features on Deception Island is the linearity of its easternmost coastal landform, the origin of which remains unknown. Some answers, based on presence of strike-slip fault or on the ice cap and beach geomorphological dynamics, have been reported in the literature. Our new work provides several indications of the existence of a dip-slip submarine fault, parallel to the coast (NNW-SSE), which suggests a tectonic origin for this morphological feature. Uplifted marine terraces, incision of a fluvial network over the ice cap, normal faulting parallel to the coast in the north and south rock heads bounding the beach and sharp shelf-break with rather constant slope, constitute some of this evidence. Terrace uplift and fluvial channel incision decreasing southward from Macaroni Point, indicates possible tilt movement across this inferred fault plane. © Antarctic Science Ltd.

Descripción: Jubanyella plemmyris, a new genus and species of aeginid narcomedusan, is described from one complete specimen stranded on Potter Cove beach, King George Island, Southern Ocean. The new genus and species is proposed in order to accommodate the specimen described in the family Aeginidae; Jubanyella gen. nov. contains undivided stomach pouches, therefore necessitating a new diagnosis for this family. © The Author 2006. Published by Oxford University Press. All rights reserved.

Descripción: A new species of Coulmannia, C. rossensis, is described from the Ross Sea, Antarctica. It is most similar to C. ramosae Castelló, 2004, but can easily be distinguished from this species by the males yielding a pair of granulate humps on the dorsum of the pereonites 1-6 and a single granulate hump on the pereonite 7 and the free pleonite. Coulmannia rossensis sp. n. is sexually dimorphic. Th e dorsal sculpture of the female bodies yield a single granulate hump on all the pereonites and free pleonite. Th e species of the genus Coulmannia are restricted to the Southern Ocean, and C. rossensis sp. n. is the fourth species included in it. © M. Choudhury et al.

Descripción: The distribution and abundance of gymnosome gastropods in the Argentine Sea and Brazil--Malvinas Confluence during 1978-1979 and 1988 were studied. The collections analyzed included 768 quantitative samples obtained between 48°W and the coast, and from 35°S to 55°S. Two species were found. Spongiobranchaea australis was the most frequent and abundant (up to 730 per 1000 m3); its presence in the area was associated with the core of the Malvinas Current. Clione antarctica was less abundant (maximum abundance: 230 per 1000 m3) and was also associated with the Malvinas Current. The geographic ranges of both species in the area are wider than previously described. Since the range of S. australis in the area extends far from the range of its prey Clio, it is not clear whether S. australis can feed on the thecosomatous pteropod Limacina (and not only on Clio, as described in the bibliography) or it starves in that area. During the 1978-1979 annual cycle, the abundance of both species followed neither the abundance patterns of their prey nor of the total zooplankton, and differed from each other. The residence time of swarms of both gymnosomes were shorter than one month. As a general pattern, the aggregates are rapidly transported northward by the Malvinas Current and also penetrate the outer shelf water, but they remain there only during a short period and cannot preclude the final expatriation. So, the abundance of gymnosomes in the area depends on passive migration more than intrinsic population factors.

Descripción: The Larsen Basin is the depositional area including all the upper Mesozoic-lower Cenozoic sedimentary rocks on the continental shelf of the northern Antarctic Peninsula. The western boundary between the basin fill and the rocks forming its technical basement, is not exposed, and was defined on the basis of aeromagnetic data. On petrological grounds, the Mesozoic marine sedimentary rocks exposed on western Tabarin Peninsula, at the north-eastern extremity of the Antarctic Peninsula, are assigned to the lower part of the Aptian-Eocene regressive megasequence that forms the basin filling. These rocks are faulted against sediments of the Antarctic Peninsula magmatic arc, suggesting that post- depositional tectonic movements probably occurred. This compressional deformation is assigned to mid-Cretaceous times, when the Coniacian partial basin inversion was accompanied by westward-verging deformation at the western basin margin. Although the original extent of the basin cannot be discerned from these data, the lithostratigraphical evidence and geographical position of the basin sediments, together with terrestrial magnetic data, confirm that the Larsen Basin extends onto the southern part of Tabarin Peninsula, and indicate that the western limit of the basin is located northward of the previously proposed limit. © 2004 Asociación Geológica Argentina.

Descripción: A series of acyl esters of 3,17-β-estradiol has been prepared by an enzymatic methodology. Eleven 17-monoacyl products (five novel compounds) were obtained in a highly regioselective way by acylation of 3,17-β-estradiol or by alcoholysis of the corresponding diacyl derivatives. The influence of various reaction parameters such as molar ratio, enzyme:substrate ratio and temperature was evaluated. Among the tested lipases, Candida rugosa lipase appeared to be the most appropriate in monoacylation and lipase from Candida antarctica in alcoholysis. The advantages presented by this methodology such as mild reaction conditions, economy and low environmental impact, make the biocatalysis a convenient way to prepare monoacyl derivatives of 3,17-β-estradiol containing the aromatic 3-hydroxyl group free. Some of these compounds are recongnized as useful products in the pharmaceutical industry. ©ARKAT.

Descripción: We investigated the selective predation of mixotrophic and heterotrophic flagellates (MF and HF) on different heterotrophic prokaryote phylotypes (HPP; Bacteria + Archaea) living in natural assemblages from oligotrophic Antarctic lakes. In situ prey preference was analyzed for the first time on different mixotrophic taxa (Pseudopedinella sp., Ochromonas-like cells, Chrysophyceae >5 μm). The relative abundances of seven different HPP hybridized by CARD-FISH (catalyzed reporter deposition-fluorescent in situ hybridization) in natural community were compared with the proportions of hybridized cells inside digestive vacuoles. Our results showed some general trends to selectivity over some HPP. Alphaproteobacteria and Betaproteobacteria were the most abundant groups, and strikingly, a negative selection trend was detected in most samples by all bacterivorous protists. In contrast, for Actinobacteria a positive selection trend was observed in most samples, whereas Bacteroidetes seemed to be randomly preyed upon. Interestingly, similar prey preferences were observed in all bacterivorous flagellates. Our results suggest that phylogenetic affiliation determines part of the process of prey selection by protists in these lakes. Nevertheless, other features, such as cell size, morphology and the presence of the S-layer, might also significantly contribute to prey selectivity on the HPP. © 2012 The Author 2012. Published by Oxford University Press. All rights reserved.

Descripción: Coupling between pelagic and benthic systems has been described in numerous shallow water communities. In Potter Cove, where pelagic primary production is low (not only during the Antarctic winter but also during the summer), the rich benthic community present there must depend on other food sources than phytoplankton. Over a year-round period we determined the abundance of the different seston particles which constituted the stomach contents of the Antarctic ascidian Cnemidocarpa verrucosa (Lesson, 1830) at Potter Cove. Stomach repletion was highest in November and lowest in June. Ascidians took in a wide range of particles from large detritus (macroalgal debris and faecal pellets) to minute particles < 5 μm. Large detritus and minute particles together represent the main percentage of contents throughout the year (mean 91%). Diatoms were a low percentage (mean 4.5%). Unidentified flagellates, dinoflagellates and coccolithophorids were scarce, with mean values lower than 4%. Among diatoms benthic species were more abundant in summer and pelagic ones prevailed from March to November. Resuspension of benthic material due to wind mixing and the input of allochthonous particles by currents are important mechanisms that ensure food for ascidians and the community of suspension feeders in Potter Cove.

Descripción: We first study the seasonal and geographical behavior of gravity wave activity in the lower stratosphere over the southernmost Andes mountains and their prolongation in the Antarctic Peninsula by global positioning system (GPS) radio occultation (RO) temperature profiles, obtained between years 2002 and 2005 by the CHAllenging Minisatellite Payload (CHAMP) mission. The observed features complement observations in the same zone by other satellite passive remote sensing instruments, which are able to detect different height regions and other spectral intervals of the wave spectrum. Comparisons with previous GPS RO studies in smaller areas than the one covered in our analysis are also established. Significant seasonal variation of wave activity is observed in our work, in agreement with results from other instruments. The locations of significant cases indicate that topography is an important source. Some strong wave activity is also found over open ocean. Critical level filtering is shown to have an attenuation effect, implying that a large fraction of the observed activity can be considered to be an outcome of mountain waves. The studied region has a significant advantage as compared to other regions of our planet: it generates wavefronts nearly aligned with the North-South direction (almost parallel to the mountains), whereby this geometry favors the wave detection by the nearly meridional line of sight characterizing most of the GPS RO observations used. A distribution of the observed gravity waves in terms of amplitudes and wavelengths is also presented.

Descripción: A psychrotolerant marine bacterial strain, designated JUB59 T, was isolated from Antarctic surface seawater and classified as a new species of the genus Bizionia. Here, we present the first draft genome sequence for this genus, which suggests interesting features such as UV resistance, hydrolytic exoenzymes, and nitrogen metabolism. © 2011, American Society for Microbiology.

Descripción: Three water bodies of contrasting trophic status located at Hope Bay (Antarctic Peninsula) were studied during the summer of 1999, analysing all of their planktonic communities (zooplankton, phytoplankton and bacterioplankton) and their main limnological features. Important differences associated with their trophic conditions were found among lakes. At one extreme of the gradient, in the most oligotrophic lake (Lake Chico), the nektobenthic copepod Boeckella poppei and the rotifer Philodina gregaria were dominant in the open waters, and copepods presented a single reproductive event (univoltine life cycle); phytoplankton exhibited the lowest densities, dominated by nanoplanktonic Chrysophyceae and picocyanobacteria. In the meso-eutrophic Lake Boeckella, B. poppei, the dominant zooplankter, exhibited a multivoltine life cycle; phytoplankton were mainly represented by nanoplanktonic species of Volvocales, alternating with flagellate Chrysophyceae, and a great abundance of picocyanobacteria. In the hypertrophic Pingüi Pond, zooplankters were exclusively represented by bdelloid rotifers and ciliates; phytoplankton samples included some strictly planktonic species (Volvocales), a great proportion of picocyanobacteria and many typically benthic species (oscillatorians and diatoms) due to the shallowness of the water body. Bacterioplankton densities did not show important differences among lakes, but fluctuations, probably associated with a top-down control, were observed in the hypertrophic pond. This paper constitutes the first survey concerning all the planktonic compartments of water bodies of different trophic status at Hope Bay, describing the relative contributions of autotrophic and heterotrophic components to their food webs.

Descripción: Above the southern Andes range and its prolongation in the Antarctic Peninsula, large-amplitude mountain and shear gravity waves observed with Weather Research and Forecasting (WRF) mesoscale model simulations during winter 2009 are analyzed. Two specific reasons motivated this study: (1) a decade of satellite observations of temperature fluctuations in the stratosphere, allowing us to infer that this region may be launching the largest-amplitude gravity waves into the upper atmosphere, and (2) the recent design of a research program to investigate these features in detail, the Southern Andes Antarctic Gravity wave Initiative (SAANGRIA). The simulations are forced with ERA-Interim data from the European Centre for Medium-Range Weather Forecasts. The approach selected for the regional downscaling is based on consecutive integrations with weekly reinitialization with 24 h of spin-up, and the outputs during this period are excluded from the analysis. From 1 June to 31 August 2009, five case studies were selected on the basis of their outstanding characteristics and large wave amplitudes. In general, one or two prevailing modes of oscillation are identified after applying continuous wavelet transforms at constant pressure levels and perpendicularly to the nominal orientation of the dominant wave crests. In all cases, the dominant modes are characterized by horizontal wavelengths around 50 km. Their vertical wavelengths, depending on a usually strong background wind shear, are estimated to be between 2 and 11 km. The corresponding intrinsic periods range between 10 and 140 min. In general, the estimated vertical wavelength (intrinsic period) maximizes (minimizes) around 250-300 hPa. The synoptic circulation for each case is described. Zonal and meridional components of the vertical flux of horizontal momentum are shown in detail for each case, including possible horizontal wavelengths between 12 and 400 km. Large values of this flux are observed at higher pressure levels, decreasing with increasing height after a progressive deposition of momentum by different mechanisms. As expected, in the wintertime upper troposphere and lower stratosphere in this region, a prevailing zonal component is negative almost everywhere, with the exception of one case above the northern tip of the Antarctic Peninsula. A comparison with previous experimental results reported in the region from in situ and remote sensing measurements suggests a good agreement with the momentum flux profiles computed from the simulations. Partial wave reflection near the tropopause was found, as considerable departures from equipartition between potential and kinetic wave energy are obtained in all cases and at all pressure levels. This ratio was always less than 1 below the lower stratosphere. Copyright 2012 by the American Geophysical Union.

Descripción: The response of altered sex ratio in southern elephant seals due to environmental stress was analysed. Data were collected at King George Island from 1980 to 1994. Significant retreats in the ice cover during El Niño events strongly suggest environmental stress during this period along the Bellingshausen Sea, a zone where female elephant seals from King George Island feed during their pregnancy. Randomly chosen weaning elephant seal pups (n = 1178) were sexed at Stranger Point (King George Island, 62° 14' S, 58° 30' W) over 5 km of beach from 1985 to 1994. Adult sex ratio was also determined annually from 1980 to 1994 as the ratio between maximum number of bulls and females on land. The theoretical pup sex ratio was assumed as 1:1 according to background information. Adult sex ratio was calculated as 1:6. To define the occurrence of El Niño Southern Oscillation (ENSO) during the study period, a sea surface temperature (SST) index called 'Niño 3.4' for the region 5°N to 5° S, 120° E to 170° W was considered. Monthly SST anomalies were obtained from the Climate Prediction Center (CPC, NOAA). To provide an annual index of anomaly strength (IAS), the monthly adjusted oscillation index climatology (AOIC) was averaged. Accumulated values during the whole study period showed that during El Niño years (1987, 1991, 1992) the proportion of pups was significantly biased in favour of females (p < 0.01). During normal years (1986, 1990, 1993, 1994) and La Niña years (1985, 1988, 1989), accumulative values showed a greater proportion of male pups to females (p < 0.05), Using the 1:1 hypothesis, we found during El Niño years a 9% reduction in the male segment, whereas in non-El Niño years a recovery of 7 % was observed (3 % during normal years and 4 % during La Niña years. To see the influence of accumulative values of pup sex ratio in adult sex ratio, a theoretical adult proportion was calculated as 1:6. To test this hypothesis, information on adult sex ratio taken from King George Island between 1980 and 1994 (n = 14 yr) was analysed. The average adult sex ratio for King George Island was 1:7. This value seems to confirm the hypothesis that this population has had a balanced production of male and female pups in the long term. Comparisons with Pacific and Indian declining seal populations were made.