A complete arc-trench system recognized in Gondwana sequences of the Antarctic Peninsula region

first_imgPrior to Late Triassic–Early Jurassic times, the geological history of the Antarctic Peninsula region was dominated almost entirely by Gondwana sequences that together comprised a major arc-trench system. Subduction complex, trench-slope-break and fore-arc basin sedimentation can all be recognized, and deposition was at least partly on early Palaeozoic or older continental crust. The only evidence for a contemporaneous magmatic arc situated in the Antarctic Peninsula at this time consists of patchy occurrences of metavolcanic rocks, possibly representing the frontal edge of the arc, and the major outcrop area of these rocks is believed to lie under the broad shallow continental shelf E of the Antarctic Peninsula. This is contrary to most current hypotheses in which a marginal basin, presumably floored by oceanic crust, is thought to crop out close to the E coast of the Antarctic Peninsula. However, the complete absence of substantial outcrops of pre-Jurassic volcanic rocks anywhere in eastern Antarctica and South Africa, which are the closest and most likely places in which these should exist, supports the new proposal. Moreover, the identification of back-arc elements of the arc-trench system (foreland fold-thrust belt and retro-arc foreland basin) in eastern Antarctica and South Africa greatly strengthens the likelihood of the arc cropping out in the area suggested. Towards the end of the Triassic and during the Early Jurassic Periods, an intense diastrophic event, or culmination of events, of orogenic magnitude occurred (Gondwanian orogeny), causing substantial redistribution of the pre-existing elements of the arc-trench system. In particular, all the fore-arc sequences were strongly deformed, some possibly for the first time (e.g. in the fore-arc basin), and became firmly accreted to the continental margin. Moreover, the magmatic foci migrated trenchwards to intrude the deformed rocks in the Antarctic Peninsula. Because many of the plutons were emplaced synkinematically, they often closely resemble ‘basement’ gneisses. The distinction between these rocks remains a serious problem in the Antarctic Peninsula and it can be solved only partially by radiometriclast_img read more

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Some aspects of feeding in the Antarctic krill, Euphausia superba

first_imgThe interaction between feeding activity, swarming behaviour and vertical migration in Antarctic krill, Euphausia superba Dana, was examined by a combination of laboratory physiology studies and intensive field sampling of a patch of krill located NE of South Georgia, in April 1980. The combined use of echolocation and a series of timed net hauls from discrete depth horizons revealed a diurnal rhythm of swarming behaviour, vertical migration and gut fullness. Laboratory physiological data showed that krill will filter feed throughout the 24 h but with peak activity by night, and that filtration rate is affected by krill density. Biochemical studies in vitro indicated that rates of lipid synthesis are generally highest at the surface and by night. These results are discussed in relation to other studies of krill feeding activity and suggestions made for further research.last_img read more

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Seasonal variation in respiratory and photosynthetic parameters in three mosses from the maritime Antarctic

first_imgCarbon fixation under controlled conditions was measured in three mosses from the maritime Antarctic using an infra-red gas analysis system. Gas exchange parameters were determined during each season in 1993 and 1994 using the Arrhenius equation and a hyperbolic tangent function applied to respiration and photosynthesis, respectively. Environmental data was collected in 1994 for comparison. All seasonal variations were greater inBrachythecium than in the species from less hydric habitats. Respiration rates were highest in summer and lowest in winter at all temperatures inBrachythecium, but there was little change inChorisodontium orAndreaea . There was some seasonal variation in the initial slope (Kp) of the photosynthesis-irradiance curve in all species, although the environmental data suggested that this was of little ecological importance. In all species seasonal changes in the maximum rates of photosynthesis (GPmax, NPmax) were observed, generally with a pattern of summer maxima, although there were some interannual differences. These changes are considered to be the most important in affecting the overall annual productivity of the mosses. There were no seasonal variations in the optimum temperatures for either gross or net photosynthesis, or for the irradiance at the onset of light saturation (Ik). The results have important implications for the use of models to estimate the productivity of the Antarctic flora based upon present or predicted climate data.last_img read more

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An investigation into the roles of ECH and whistler mode waves in the formation of ‘pancake’ electron distributions using data from the CRRES satellite

first_imgElectron pitch angle distributions sharply peaked at 90 degrees pitch angle were first recorded in the energy range 50 eV < E < 500 eV by the GEOS-1 and GEOS-2 spacecraft in 1977/8, from the plasmapause out to geostationary orbit. At the time they were explained as the remnants of pitch angle diffusion driven solely by Electron Cyclotron Harmonic (ECH) waves. Here we use observations by instruments on board the CRRES spacecraft to study these distributions in more detail. The pancake distributions are now seen to develop from injected distributions that are nearly isotropic in velocity space, on a time scale that is greater than 2 hours. The freshly injected distributions are associated with strong ECH and whistler mode waves suggesting that the pancake distributions are likely to be caused by a combination of both wave types. Our results suggest that whistler mode waves play a dominant role in the formation of pancake distributions outside L = 6.0, whereas inside L = 6.0 and, in particular, in the vicinity of the plasmapause, the ECH waves also play a significant role. Consequently both types of waves should be considered in any attempt to explain the diffuse aurora and the variation with L taken into account. (C) 2000 COSPAR. Published by Elsevier Science Ltd.last_img read more

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Genetic structure of Patagonian toothfish populations from otolith DNA

first_imgThe Patagonian toothfish, Dissostichus eleginoides, is a valuable fishery species and has a discontinuous distribution across the Southern Ocean. Identification of the genetic stock structure of toothfish would allow evaluation of the suitability of the spatial scale at which fisheries management operates. Genetic subdivision seems likely given the species distribution. Population genetics studies of this species have been performed; however, they have been limited by sample size, spatial coverage and/or the type of markers investigated. As a potential solution, we developed methods for extracting toothfish DNA from otoliths that are available in large numbers from collections held at several research institutes. Genetic differentiation between the three oceanic sectors was investigated. Four mitochondrial and four nuclear markers with multiple single nucleotide polymorphisms were sequenced by high throughput sequencing for samples from six locations. Genetic differentiation was found between three sectors with nuclear markers. However, only the Pacific sector was differentiated from other sectors with mitochondrial markers. This study demonstrates the usefulness of otolith DNA as a means of increasing sample sizes for population genetics research of fish. Additionally, the combination of nuclear and mitochondrial markers may allow insight into how the observed differences in movements between male and female toothfish impact population structure.last_img read more

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Delivering sustained, coordinated and integrated observations of the Southern Ocean for global impact

first_imgThe Southern Ocean is disproportionately important in its effect on the Earth system, impacting climatic, biogeochemical and ecological systems, which makes recent observed changes to this system cause for global concern. The enhanced understanding and improvements in predictive skill needed for understanding and projecting future states of the Southern Ocean require sustained observations. Over the last decade, the Southern Ocean Observing System (SOOS) has established networks for enhancing regional coordination and research community groups to advance development of observing system capabilities. These networks support delivery of the SOOS 20-year vision, which is to develop a circumpolar system that ensures time series of key variables, and deliver the greatest impact from data to all key end-users. Although the Southern Ocean remains one of the least-observed ocean regions, enhanced international coordination and advances in autonomous platforms have resulted in progress towards addressing the need for sustained observations of this region. Since 2009, the Southern Ocean community has deployed over 5700 observational platforms south of 40°S. Large-scale, multi-year or sustained, multidisciplinary efforts have been supported and are now delivering observations of essential variables at space and time scales that enable assessment of changes being observed in Southern Ocean systems. The improved observational coverage, however, is predominantly for the open ocean, encompasses the summer, consists of primarily physical oceanographic variables and covers surface to 2000 m. Significant gaps remain in observations of the ice-impacted ocean, the sea ice, depths more than 2000 m, the air-sea-ice interface, biogeochemical and biological variables, and for seasons other than summer. Addressing these data gaps in a sustained way requires parallel advances in coordination networks, cyberinfrastructure and data management tools, observational platform and sensor technology, platform interrogation and data-transmission technologies, modeling frameworks, and internationally agreed sampling requirements of key variables. This paper presents a community statement on the major scientific and observational progress of the last decade, and importantly, an assessment of key priorities for the coming decade, towards achieving the SOOS vision and delivering essential data to all end users.last_img read more

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Legacy and Emerging Persistent Organic Pollutants in Antarctic Benthic Invertebrates near Rothera Point, Western Antarctic Peninsula

first_imgThe levels of pollutants in polar regions is gaining progressively more attention from the science community. This is especially so for pollutants that persist in the environment and can reach polar latitudes via a wide range of routes, such as persistent organic pollutants (POPs). In this study samples of Antarctic marine benthic organisms were analysed for legacy and emerging POPs to comprehensively assess the current POPs concentrations in Antarctic benthos and infer the potential sources of the pollutants. Specimens of 5 different benthic invertebrate species were collected in 2 distinct locations near the Rothera Research station (67°35’8″S and 68°7’59″W). Any impact of the nearby Rothera Station as a local source of pollution appeared to be negligible. The most abundant chemicals detected were HCB and BDE-209, reaching the highest concentrations in limpets and urchins, followed by sea stars, ascidians and sea cucumbers. The relative congener patterns of PCBs and PBDEs were almost the same in all species. Some chemicals (e.g. Heptachlor, Oxychlordane and Mirex) were detected in the Antarctic invertebrates for the first time. Statistical methods revealed that the distribution of the POPs is not only driven by the feeding traits of the species, but also by the physico-chemical properties of the individual compounds. Benthic invertebrates are excellent indicators of the contaminant patterns of inshore Antarctic ecosystems.last_img read more

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Circumpolar projections of Antarctic krill growth potential

first_imgAntarctic krill is a key species of important Southern Ocean food webs, yet how changes in ocean temperature and primary production may impact their habitat quality remains poorly understood. We provide a circumpolar assessment of the robustness of krill growth habitat to climate change by coupling an empirical krill growth model with projections from a weighted subset of IPCC Earth system models. We find that 85% of the study area experienced only a moderate change in relative gross growth potential (± 20%) by 2100. However, a temporal shift in seasonal timings of habitat quality may cause disjunctions between krill’s biological timings and the future environment. Regions likely to experience habitat quality decline or retreat are concentrated near the northern limits of krill distribution and in the Amundsen–Bellingshausen seas region during autumn, meaning habitat will likely shift to higher latitudes in these areas.last_img read more

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Quiet night Arctic ionospheric D region characteristics

first_imgVLF radio propagation recordings are used to determine the characteristics of the nighttime polar lower D region of the ionosphere. Recordings of both VLF phase and amplitude in the Arctic on days within ∼1‐2 weeks of the equinoxes enable their day‐to‐night changes to be determined. These changes are then combined with previously measured daytime polar D region characteristics to find the nighttime characteristics. The previously determined daytime characteristics were measured in the Arctic summer; the NRLMSISE atmosphere model is used to help determine the height change from daytime summer to daytime equinox (∼5 km lower). The principal path used was from the 16.4 kHz Norwegian transmitter JXN (67°N, 14°E) 1334 km northwards across the Arctic Ocean to Ny‐Ålesund (79°N, 12°E), Svalbard. Also used were the 2014‐km path from NRK (37.5 kHz, Grindavik, 64°N, Iceland) to Ny‐Ålesund, the 1655‐km path from JXN to Reykjavik (64°N, Iceland) and the 5302‐km path from JXN across the Arctic Ocean to Fairbanks (65°N) in Alaska. The night values of (the Wait parameters) H’ and β were found to average from ∼79 km at equinox down to 77 km near winter solstice (lower than the 85 km at low and mid‐latitudes by ∼7 km) and 0.6 km‐1 respectively. This lower height and its variability are shown to be consistent with the principal source of ionization being energetic electron precipitation.last_img read more

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Arizona rides early lead to 6-1 victory over BYU

first_img Written by FacebookTwitterLinkedInEmailTUCSON, Arizona (April 17, 2018)—Arizona jumped out to an early lead and rode the arm of Juan Aguilera en route to a 6-1 defeat of BYU baseball on Tuesday night.Aguilera (5-0) twirled a one-hitter through six innings before surrendering his second hit of the evening as the Wildcats improved their record to 23-12.A ground-rule double prevented Arizona from getting a second run as it took a 1-0 lead into the second inning.Cougar starter Jordan Wood gathered momentum in the second frame with a pair of strikeouts and catcher David Clawson pegged the inning-ending out on a delayed steal to second. That momentum was short-lived as Arizona built a 6-0 lead through three-plus innings.The Cougar offense sputtered. Aguilera beaned Mitch McIntyre to start the third, but the Cougar freshman tried to steal second to no avail. A double play erased Brennon Anderson’s leadoff single in the fourth.Reliever Rhett Parkinson got out of a jam with Wildcats on second and third, fanning his third Arizona batter in as many innings to end the sixth frame.When McIntyre got a one-out single and Jarrett Perns drew a base on balls in the eighth from the Wildcats’ first reliever, it set the table for Anderson’s second single of the night. That single to left field plated McIntyre.The Cougars, now 18-16, take a break for final exams before hosting Utah on Tuesday.​ April 18, 2018 /Sports News – Local Arizona rides early lead to 6-1 victory over BYU Tags: Baseball/BYU Cougars Robert Lovelllast_img read more

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