Nutrients and their effects on phytoplankton populations in lakes on Signy Island, Antarctica

first_imgSeasonal changes in nutrient concentrations, phytoplankton biomass and nutritional state were followed in two contrasting Antarctic lakes. Oligotrophic Sombre Lake receives little phosphate from its catchment and this limits the standing crop of phytoplankton which can develop in spring and summer. This situation appears to be typical of unenriched Maritime Antarctic lakes. Large numbers of seals and seabirds in the catchment of nearby Heywood Lake increase its phosphate loading and allow a much denser growth of phytoplankton. The N:P ratio is low and nitrogen rather than phosphate is the most limiting nutrient. Despite limitation of standing crop, photosynthetic rates in both lakes are relatively high and recycling of nutrients within the lake may be rapid.last_img read more

A visualization-based post-processing system for analysis of acoustic data

first_imgA commercial data-visualization package, AVS, and database are used as the basis for a powerful and highly flexible acoustic data analysis system. The system is easy to use and can be modified by the user to incorporate novel visualization and analysis capabilities as required. Multi-frequency ping-by-ping or integrated data from a variety of echo-sounders may be viewed and manipulated within the system. Here, we describe the main features of the system and illustrate how it may be used to mark, transform, analyse, and compare dual-frequency acoustic data.last_img read more

The last inoceramid bivalves in Antarctica

first_imgThe last inoceramid bivalves in Antarctica are no younger than mid- to late Campanian in age. They occur within the Herbert Sound and Rabot Point members of the Santa Marta Formation, which is the lowermost of four component formations within the Late Cretaceous-earliest Tertiary Marambio Group, James Ross Basin. These inoceramids comprise an unusual giant form which is assigned herein toAntarcticeramus rabotensisgen. et sp. nov. Moderately inequivalve and gryphaeoid in form,Antarcticeranusis characterized by a larger and more inflated right valve with a rounded-trapeziform to obliquely elongated outline. Almost all right valves have a sharply defined, shelf-like anterior margin. The left valve is less obviously obliquely elongated and only weakly inflated. Ornament appears to have consisted of low, commarginal folds. There are indications of a possible phylogenetic connection betweenAntarcticeramusandSphenoceramusJ. Böhm, 1915. Antarcticeramus rabotensisgen. et sp. nov. is extremely abundant at certain levels within the Rabot Point Member. It can be demonstrated that the majority of these specimens occur in life position and show a preferred orientation with respect to a horizontal substrate. This is taken as evidence of a positive response to prevailing water currents (rheotaxis), perhaps to enhance the process of filter feeding. Associated sparse macrofossils and abundant trace fossils indicate aerobic bottom conditions at mid-shelf depths. It is postulated that the evolution of giant size was primarily an antipredatory device. However, just as large, benthic predators were radiating in the latest Cretaceous, seawater temperatures in the southern high latitudes were beginning to fall. In the end, secretion of such large calcitic shells may have become physiologically impractical.last_img read more

The terrestrial micro-arthropod fauna of the South Sandwich Islands

first_imgThe South Sandwich Islands are an isolated maritime Antarctic volcanic island arc 550-600km south-east of South Georgia. The terrestrial biology of the islands, with emphasis on the unique habitats associated with volcanically warmed ground, was investigated in 1997 and compared with the data collected during the only previous (1964) terrestrial expedition to the archipelago. The terrestrial fauna includes 29 free-living micro-arthropod species (nine Collembola and 20 Acari) and two, currently unidentified, enchytraeid worms; a further eight parasitic and sublittoral Acari are recorded in the literature. Freshwater habitats are very restricted in the archipelago and no freshwater fauna was located. Supralittoral pools on a single island contained the marine isopod Cassidinopsis maculata. There are no endemic taxa and no shoreline invertebrates other than the supralittoral Archisotoma brucei (Collembola) and two Enchytraeidae. Diversity on individual islands is, in part, a function of available ice-free ground area. The majority of dominant species throughout the archipelago, Cryptopygus antarcticus (Collembola), Nanorchestes nivalis, Eupodes minutus, Alaskozetes antarcticus and Halozetes belgicae (Acarina), originate on other maritime Antarctic islands, while Ayersacarus tilbrooki (Acarina) is sub-Antarctic. Few (one to three) individuals of several other sub-Antarctic species were recorded by either 1964 or 1997 expeditions, but only Pilellus rykei (Acarina) was reported by both. None of the sub-Antarctic species thought to be associated with geothermally warmed ground in 1964 was confirmed in 1997, despite extensive sampling of the same sites. It is more probable that sub-Antarctic colonists frequently arrive on the South Sandwich Islands but are unable to establish longterm viable populations. Cryptopygus caecus, now widespread on Candlemas I., is a solitary exception to this generalization.last_img read more

Las Orogénesis del Paleozoico Inferior en el margen protoandino de América del Sur, Sierras Pampeanas, Argentina

first_imgEl margen proto-andino de Gondwana ha sido el escenario de al menos dos orogénesis desde el desmembramiento del supercontinente Rodinia al final del Neoprotrozoico, hasta el reagrupamiento de las masas continentales en Pangea al final del Carbonifero. Ambas orogénesis van precedidas de un periodo de apertura oceánica y sedimentación en márgenes pasivos y culminan en subducción oceánica con desarrollo de arcos-magmáticos de tipo cordillerano y colision de tipo continente-continente. La primera, orogénesis Pampeana, tiene lugar en el Cámbrico, en un intervalo de tiempo relativamente pequeño (535-520 Ma: etapas de subducción-arco magmático y colisión), y culmina con la acreción ortogonal de un pequeño terreno continental (terreno Pampeano) de naturaleza semiautóctona. Por el contrario, la orogénesis Famatiniana, tiene lugar en un periodo de Centro de Investigaciones Geológicas, Universidad Nacional de La Plata, Calle 1, nº 644, 1900 La Plata, 1 Argentina. Departamento de Petrología y Geoquímica, Universidad Complutense, 28040 Madrid, España. 2 Departamento de Geología, Facultad de Ciencias, Universidad Nacional de Córdoba, Argentina. 3 Centro Regional de Investigaciones Científicas y Técnicas La Rioja (CRILAR). Entre Ríos y Mendoza 4 (5301), Anillaco, La Rioja. Argentina. British Antarctic Survey, Isotope Geosciences Laboratory, Keyworth, Nottingham NG12 5GG, Gran 5 Bretaña CSIC, Instituto de Agrobiología y Recuersos Naturales, Salamanca, España. 6 23 C. W. Rapela, C. Casquet, E. Baldo, J. Dahlquist, R. J. Pankhurst, C. Galindo y J. Saavedra tiempo más dilatado, durante el Ordovícico y Silúrico (499-435 Ma). Durante esta orogénesis tuvo lugar la acreción de un terreno exótico a Gondwana, el terreno Precordillera (460 Ma). Este terreno está constituido por un basamento grenvilliano (aprox. 1.1Ga) y una cubierta sedimentaria de plataforma carbonatada de edad Cámbrico-Ordovícico. La acreción al margen de Gondwana fue probablemente oblicua, y el margen oriental del terreno Precordillera fue afectado por fuerte deformación y metamorfismo regional. El basamento de los cinturones andinos del Paleozoico Superior y Mesozoico situados al oeste de la Precordillera, parece estar constituido también por rocas metamórficas grenvillianas; con lo cual, gran parte de los Andes centrales entre los 26ºS y 34ºS se encuentra asentado sobre terrenos alóctonos. En cualquier caso, la paleogeografía de las masas continentales involucradas en la colisión de los terrenos exóticos durante el Paleozoico Inferior no se conoce bien todavía.last_img read more

A model for the consolidation of rafted sea ice

first_imgRafting is one of the important deformation mechanisms of sea ice. This process is widespread in the north Caspian Sea, where multiple rafting produces thick sea ice features, which are a hazard to offshore operations. Here we present a one-dimensional, thermal consolidation model for rafted sea ice. We consider the consolidation between the layers of both a two-layer and a three-layer section of rafted sea ice. The rafted ice is assumed to be composed of layers of sea ice of equal thickness, separated by thin layers of ocean water. Results show that the thickness of the liquid layer reduced asymptotically with time, such that there always remained a thin saline liquid layer. We propose that when the liquid layer is equal to the surface roughness the adjacent layers can be considered consolidated. Using parameters representative of the north Caspian, the Arctic, and the Antarctic, our results show that for a choice of standard parameters it took under 15 h for two layers of rafted sea ice to consolidate. Sensitivity studies showed that the consolidation model is highly sensitive to the initial thickness of the liquid layer, the fraction of salt release during freezing, and the height of the surface asperities. We believe that further investigation of these parameters is needed before any concrete conclusions can be drawn about rate of consolidation of rafted sea ice features.last_img read more

EPICA Dome C record of glacial and interglacial intensities

first_imgClimate models show strong links between Antarctic and global temperature both in future and in glacial climate simulations. Past Antarctic temperatures can be estimated from measurements of water stable isotopes along the EPICA Dome C ice core over the past 800 000 years. Here we focus on the reliability of the relative intensities of glacial and interglacial periods derived from the stable isotope profile. The consistency between stable isotope-derived temperature and other environmental and climatic proxies measured along the EDC ice core is analysed at the orbital scale and compared with estimates of global ice volume. MIS 2,12 and 16 appear as the strongest glacial maxima, while MIS 5.5 and 11 appear as the warmest interglacial maxima. The links between EDC temperature, global temperature, local and global radiative forcings are analysed. We show: (i) a strong but changing link between EDC temperature and greenhouse gas global radiative forcing in the first and second part of the record; (ii) a large residual signature of obliquity in EDC temperature with a 5 ky lag; (iii) the exceptional character of temperature variations within interglacial periods. Focusing on MIS 5.5, the warmest interglacial of EDC record, we show that orbitally forced coupled climate models only Simulate a precession-induced shift of the Antarctic seasonal cycle of temperature. While they do capture annually persistent Greenland warmth, models fail to capture the warming indicated by Antarctic ice core delta D. We suggest that the model-data mismatch may result from the lack of feedbacks between ice sheets and climate including both local Antarctic effects due to changes in ice sheet topography and global effects due to meltwater-thermohaline circulation interplays. An MIS 5.5 sensitivity study conducted with interactive Greenland melt indeed induces a slight Antarctic warming. We suggest that interglacial EDC optima are caused by transient heat transport redistribution comparable with glacial north-south seesaw abrupt climatic changes. (C) 2009 Elsevier Ltd. All rights reserved.last_img read more

Poa pratensis L., current status of the longest-established non-native vascular plant in the Antarctic

first_imgA single colony of the non-native grass Poa pratensis L., which was introduced inadvertently to Cierva Point, Antarctic Peninsula, during the 1954–1955 season, was still present during a survey in February 2012, making it the longest surviving non-native vascular plant colony known in Antarctica. Since 1991, the grass cover has roughly tripled in size, with an annual increase in area of approximately 0.016 m2, and an estimated maximum radial growth rate of 1.43 cm y−1. However, it remains restricted to the original site of introduction and its immediate surroundings (c. 1 m2). Annual flowering of the plants occurred during the 2010/2011 and 2011/2012 seasons; however, there has been no seed production and only incomplete development of the sexual structures. Current environmental conditions, including low temperatures, may inhibit sexual reproduction. Lack of effective vegetative dispersal may be influenced by the low level of human activity at the site, which limits opportunities for human-mediated dispersal. Although P. pratensis has existed at Cierva Point for almost 60 years, it has not yet become invasive. Scenarios for the potential future development of the species in Antarctica and the associated negative impacts upon the native vegetation from competition are discussed in the context of regional climate change. Finally, we describe the environmental risk presented by P. pratensis and argue that this non-native species should be eradicated as soon as possible in accordance with the Protocol on Environmental Protection to the Antarctic Treaty.last_img read more

Evolutionary factors affecting the cross-species utility of newly developed microsatellite markers in seabirds

first_imgMicrosatellite loci are ideal for testing hypotheses relating to genetic segregation at fine spatio-temporal scales. They are also conserved among closely related species, making them potentially useful for clarifying interspecific relationships between recently diverged taxa. However, mutations at primer binding sites may lead to increased non-amplification, or disruptions that may lead to decreased polymorphism in non-target species. Furthermore, high mutation rates and constraints on allele size may also lead, with evolutionary time, to an increase in convergently evolved allele size classes, biasing measures of interspecific genetic differentiation. Here, we used next-generation sequencing to develop microsatellite markers from a shotgun genome sequence of the sub-Antarctic seabird, the thin-billed prion (Pachyptila belcheri), that we tested for cross-species amplification in other Pachyptila and related sub-Antarctic species. We found that heterozygosity decreased and the proportion of non-amplifying loci increased with phylogenetic distance from the target species. Surprisingly, we found that species trees estimated from interspecific FST provided better approximations of mtDNA relationships among the studied species than those estimated using DC, even though FST was more affected by null alleles. We observed a significantly non-linear second order polynomial relationship between microsatellite and mtDNA distances. We propose that the loss of linearity with increasing mtDNA distance stems from an increasing proportion of homoplastic allele size classes that are identical in state, but not identical by descent. Therefore, despite high cross-species amplification success and high polymorphism among the closely related Pachyptila species, we caution against the use of microsatellites in phylogenetic inference among distantly related taxa.last_img read more

Two women resign from NFL domestic violence group, calling it a ‘fig leaf’

first_img Beau Lund FacebookTwitterLinkedInEmailiStock/Thinkstock(NEW YORK) — Two female domestic violence experts resigned from the commission created by the National Football League’s Players Association, saying their suggestions had been ignored and the change within the organization had been insufficient.Deborah Epstein, who is the co-director of Georgetown University’s Law Center Domestic Violence Clinic, and Susan Else, former president of the National Network to End Domestic Violence, both resigned from the NFLPA’s commission on domestic violence.Epstein described her work with the commission and the grievances that prompted her resignation in an op-ed that was published Tuesday in The Washington Post.“Because I care deeply about violence against women in the NFL and beyond, I can no longer continue to be part of a commission that is essentially a fig leaf,” Epstein wrote.The National Football League’s Players Association released a statement in response to the op-ed.“We respect the decision of Deborah Epstein and Susan Else to resign from our commission. We have implemented many of the commission’s recommendations during the past few years and will continue to provide resources and services to our members,” the NFLPA said in a statement to ABC News.Epstein described her four years working with the group as being “by turns, promising, inspiring and deeply frustrating.”She said the commission was started in a “belated effort to confront the plague of domestic violence” in the league, and the “precipitating event” that led to the commission’s formation was the public release of surveillance footage showing then-Ravens player Ray Rice hitting and dragging his then-fiancee in a casino elevator in 2014.A study by the commission provided recommendations for how to address the issue of domestic violence. Epstein, however, did not disclose specific findings from the group’s research in The Washington Post, explaining that she signed a confidentiality agreement at the players’ association’s insistence.The study, which she said “made numerous systematic recommendations of concrete steps that would go a long way toward dramatically lowering the risk of domestic violence in professional football,” was completed in June 2016. Epstein noted that the commission had only met three times “despite my numerous requests.”“As of our last meeting, the NFLPA had not implemented any of the reforms proposed in our study,” she wrote.A spokesperson for the NFLPA told ABC News that a number of recommendations made by Epstein have been implemented. The recommendations included the hiring of a director of wellness who is a trained clinician, in depth crisis training for player-facing staff, greater emphasis on marriage counseling and enrichment events focused on couples. The spokesperson also said it was Epstein’s idea for the study.The NFLPA has to lobby the league for any and all suggested changes, and the league has to approve policies before they can be implemented.Epstein said she gave suggestions for projects that could “help reduce intimate-partner violence in the domain of professional football” but they were ignored.“My NFLPA contacts would initially greet these ideas with a burst of enthusiasm and an indication of likely implementation, but efforts to follow up would yield nothing in the way of specific plans, and eventually communication would fade into radio silence,” she wrote.She received a one-line response from NFLPA following her resignation.“The email was short, but its message couldn’t have been clearer,” she wrote.Copyright © 2018, ABC Radio. All rights reserved. June 6, 2018 /Sports News – National Two women resign from NFL domestic violence group, calling it a ‘fig leaf’center_img Written bylast_img read more