The population dynamics of Notothenia rossii from South Georgia (Antarctica)

The population dynamics of nearshore juvenile Notothenia rossii were studied at South Georgia during 1978 and 1979. Mortality of the population was calculated from length-class abundance of fish sampled by trammel nets, and the population size estimated using a mark and recapture technique. Instantaneous natural mortality in the nearshore population was high (M=0.78) although other author’s estimate for the mortality in the offshore population was only 0.35. Therefore it is likely that no single estimate of mortality will apply to fish of all ages. The population density of juvenile N. rossii was about 11 g m-2 nearshore. The size of the offshore population was estimated by calculating survival from the nearshore age classes. The data suggest that the population around South Georgia has been reduced by overfishing to about one tenth of its previous unexploited level. Yield could have been increased by fishing less intensively, and the population maintained at or near its initial level if recruitment remained constant. read more

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Magmatism and the causes of continental break-up

first_imgA two-day meeting of the Tectonic Studies Group was held in London at the Geological Society on 3-4 October 1991, to consider relationships between continental extension, super continent break-up, magmatism and mantle plumes. The approach was multidisciplinary, with contributions from geophysists, geochemists and tectonic geologists. There were 28 talks and 11 poster presentations, with about 150 people attending. The conference was opened by convenor B. C. Storey (British Antarctic Survey, Cambridge) followed by a session on relevant geophysical and geochemical principles. D. L. Anderson (California Institute of Technology) gave a stimulating keynote lecture on mantle reservoirs and seismic tomographic evidence for mantle circulation. He suggested that the source of all ‘enriched’ basalts such as ocean island basalt (OIB) and continental flood basalt was in a shallow mantle layer relative to the source of depleted mid-ocean ridge basalt (MORB). He presented new, high resolution global seismic tomography data, and argued from these that deep-rooted hot mantle up-wellings underlie mid-ocean ridges and back arc basins, but that mantle plumes, as narrow jets underlying hot spots cannot be oberved by seismic means, nor are required by geochemical data. M. A. Menzies (Royal Holloway and Bedford New College) reviewed the penological, age and thickness variations in continental lithospheric mantle, and its suitability as a mantle source for continental basalts. He described reaction zones and metasomatic fronts generated by intrusion of magmas into mantle rock, and argued that such processes generate a range of mantle compositions like those of source regions of continental flood basalts.last_img read more

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Experimental and theoretical fracture mechanics applied to Antarctic ice fracture and surface crevassing

first_imgRecent disintegration of ice shelves on the Antarctic Peninsula has highlighted the need for a better understanding of ice shelf fracture processes generally. In this paper we present a fracture criterion, incorporating new experimental fracture data, coupled with an ice shelf flow model to predict the spatial distribution of surface crevassing on the Filchner-Ronne Ice Shelf. We have developed experiments that have enabled us to quantify, for the first time, quasi-stable crack growth in Antarctic ice core specimens using a fracture initiation toughness, Kinit, for which crack growth commences. The tests cover a full range of near-surface densities, ρ = 560–871 kg m−3 (10.9–75.7 m depth). Results indicate an apparently linear dependence of fracture toughness on porosity such that Kinit = 0.257 ρ-80.7, predicting a zero-porosity toughness of Ko = 155 kPa m1/2. We have used this data to test the applicability to crevassing of a two-dimensional fracture mechanics criterion for the propagation of a small sharp crack in a biaxial stress field. The growth of an initial flaw into a larger crevasse, which involves a purely tensile crack opening, depends on the size of the flaw, the magnitude of Kinit and the nature of the applied stress field. By incorporating the criterion into a stress map of the Filchner-Ronne Ice Shelf derived from a depth-integrated finite element model of the strain-rate field, we have been able to predict regions of potential crevassing. These agree well with satellite imagery provided an initial flaw size is assumed in the range 5–50 cm.last_img read more

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Circulation and melting beneath George VI Ice Shelf, Antarctica

first_imgIntroductionGeorge VI Ice Shelf, sandwiched between the western coast of Palmer Land and the eastern coast of Alexander Island, is the largest and most studied of the west AntarcticPeninsula ice shelves. It covers an area of approximately 25,000 km2 and is underlain by Circumpolar Deep Water (CDW), with temperatures in excess of 1ºC, giving rise to rapid basal melting (Bishop and Walton, 1981; Lennon et al., 1982). The maximum ice thickness of about 500 m occurs about 70 km from the southern ice front, where a ridge of thick ice extends across George VI Sound (near 70ºW, see Figure 1) effectively dividing the upper water column into northern and southern regions. The northern ice front, which faces Marguerite Bay, appears to be near the geographical limit of ice shelf viability and hasundergone a gradual retreat in recent decades (Lucchitta and Rosanova, 1998), a timeframe over which much of the nearby Wordie Ice Shelf disintegrated (Doake and Vaughan, 1991). There is extensive surface melting over the northern parts of the ice shelf and much of the ice column near the northern ice front appears to be temperate (Paren and Cooper, 1986). Conditions in the south, where the ice front faces into Ronne Entrance, are colder and the icefront position appears to be steady. The vast majority of the flow into the ice shelf comes from Palmer Land, but basal melting is sufficient to remove most of this, so that the ice is derived almost exclusively from local accumulation by the time it reaches the ice fronts(Potter et al., 1984). There is some evidence at the margins of the ice shelf to suggest that it may have disappeared completely during the early Holocene before reforming (Sugden and Clapperton, 1981; Bentley et al., 2005).last_img read more

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New species in the old world: Europe as a frontier in biodiversity exploration, a test bed for 21st century taxonomy

first_imgThe number of described species on the planet is about 1.9 million, with ca. 17,000 new species described annually, mostly from the tropics. However, taxonomy is usually described as a science in crisis, lacking manpower and funding, a politically acknowledged problem known as the Taxonomic Impediment. Using data from the Fauna Europaea database and the Zoological Record, we show that contrary to general belief, developed and heavily-studied parts of the world are important reservoirs of unknown species. In Europe, new species of multicellular terrestrial and freshwater animals are being discovered and named at an unprecedented rate: since the 1950s, more than 770 new species are on average described each year from Europe, which add to the 125,000 terrestrial and freshwater multicellular species already known in this region. There is no sign of having reached a plateau that would allow for the assessment of the magnitude of European biodiversity. More remarkably, 1over 60% of these new species are described by non-professional taxonomists. Amateurs are recognized as an essential part of the workforce in ecology and astronomy, but the magnitude of non-professional taxonomist contributions to alpha-taxonomy has not been fully realized until now. Our results stress the importance of developing a system that better supports and guides this formidable workforce, as we seek to overcome the Taxonomic Impediment and speed up the process of describing the planetary biodiversity before it is too late.last_img read more

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Atmosphere-ocean-ice interactions in the Amundsen Sea Embayment, West Antarctica

first_imgOver recent decades outlet glaciers of the Amundsen Sea Embayment (ASE), West Antarctica, have accelerated, thinned and retreated, and are now contributing approximately 10% to global sea level rise. All the ASE glaciers flow into ice shelves, and it is the thinning of these since the 1970s, and their ungrounding from “pinning points” that is widely held to be responsible for triggering the glaciers’ decline. These changes have been linked to the inflow of warm Circumpolar Deep Water (CDW) onto the ASE’s continental shelf. CDW delivery is highly variable, and is closely related to the regional atmospheric circulation. The ASE is south of the Amundsen Sea Low (ASL), which has a large variability and which has deepened in recent decades. The ASL is influenced by the phase of the Southern Annular Mode, along with tropical climate variability. It is not currently possible to simulate such complex atmosphere-ocean-ice interactions in models, hampering prediction of future change. The current retreat could mark the beginning of an unstable phase of the ASE glaciers that, if continued, will result in collapse of the West Antarctic Ice Sheet, but numerical ice-sheet models currently lack the predictive power to answer this question. It is equally possible that the recent retreat will be short-lived and that the ASE will find a new stable state. Progress is hindered by incomplete knowledge of bed topography in the vicinity of the grounding line. Furthermore, a number of key processes are still missing or poorly represented in models of ice-flow.last_img read more

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Growth of microalgae using nitrate-rich brine wash from the water industry

first_imgSafe and accepted limits for nitrates in drinking water are exceeded in around one-third of the groundwater bodies in Europe. Whilst anion exchange (AEX) is an effective technology to strip nitrates, the regeneration of AEX resins using saturated sodium chloride (brine) results in a significant quantity of nitrate-rich saline waste, which is currently disposed of at a substantial cost to the water industry. The aim of this research was to evaluate the viability of using AEX brine wash as a nutrient source to support microalgal growth. Experiments were carried out at laboratory and pilot scales to test which algal species were able to grow on brine wash, to determine the optimal nitrate concentration within modified growth media, and to identify whether the origin of the brine wash affected the nitrate uptake potential. In small scale laboratory experiments, five marine algal species were able to grow in modified f/2 growth media containing nitrate sourced from the brine wash. Further experiments showed that three species could grow on the modified media at nitrate concentrations from 5 to 274 mg L−1. P. tricornutum could remediate up to 6.5 mg nitrate in 50 mL cultures in laboratory scale experiments, up to 570 mg at 10 L scale and 1700 mg at 100 L scale. We found that the origin of the brine wash did not significantly affect the growth of the cultures or the amount of nitrate removal from the modified media. The algal biomass could be used effectively in biogas production in small-scale trials, although with <10% the yield from P. tricornutum biomass from standard f/2 medium. Our results suggest that it may be possible to derive value from brine wash as a sustainable source of nitrate for the growth of microalgae in bulk after optimisation.last_img read more

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Heavy metal pollution in Antarctica and its potential impacts on algae

first_imgAntarctica is not free from environmental pollutants although it is often perceived as the last pristine continent on Earth. Research stations represent one of the largest forms of anthropogenic activity and are the main source of locally derived contamination in Antarctica. Elevated levels of heavy metals such as copper (Cu), lead (Pb) and mercury (Hg) have been detected in Antarctica. Fuel combustion, accidental oil spills, waste incineration and sewage disposal are amongst the primary sources of heavy metal contaminants in Antarctica, besides natural sources such as animal excrements and volcanism. Studies on the impacts of heavy metals on biota in Antarctica have been focused mainly on invertebrates and cryptogams but not on algae. However, adverse impacts of heavy metals on sensitive algae may affect organisms at the higher trophic levels, and consequently disrupt Antarctic food chains. Heavy metals may be accumulated by algae and biomagnified through the food chain. The sensitivity and response of Antarctic algae to heavy metal toxicity have not been well studied. Robust toxicity protocols for the testing of the impacts of heavy metals on Antarctic algae need to be developed. This review aims to give an overview of the status of heavy metal pollution in Antarctica and its potential impacts on algae.last_img read more

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Scoreboard Roundup — 3/6/18

first_img FacebookTwitterLinkedInEmailiStock/Thinkstock(NEW YORK) — Here are the scores from yesterday’s sports events:NATIONAL BASKETBALL ASSOCIATION Cleveland    112  Detroit     90 Indiana       92  Milwaukee   89 Miami        125  Phoenix    103 Boston       105  Chicago     89 San Antonio  100  Memphis     98 Utah          94  Orlando     80 Portland   108  L.A. Lakers   103 NATIONAL HOCKEY LEAGUE Pittsburgh   4  Calgary   3 Buffalo      5  Toronto   3 Ottawa       3  Dallas    2 Edmonton     4  Arizona   3 Vancouver   3  N-Y Islanders   4 TOP-25 COLLEGE BASKETBALL (6) Gonzaga   88  San Francisco             60       BYU           85   (20) Saint Mary’s (Cal)   72 Written by Beau Lund Copyright © 2018, ABC Radio. All rights reserved. March 5, 2018 /Sports News – National Scoreboard Roundup — 3/6/18last_img read more

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Portland wins series opener, 4-3 over BYU

first_img Tags: Baseball/BYU Cougars/WCC Written by April 12, 2018 /Sports News – Local Portland wins series opener, 4-3 over BYU FacebookTwitterLinkedInEmailPORTLAND, Oregon (April 12, 2018)—A pair of lead-off home runs along with 15 strikeouts made the difference for the University of Portland defeating BYU 4-3 on Thursday.Cody Hawken and Daniel Lopez knocked the second pitch of the fourth and sixth innings as the Pilots tied, then grabbed the eventual lead. The win improved the Pilots record to 12-19 overall and 5-8 in the West Coast Conference, while BYU is now 17-14 and 6-7.“Jordan (Wood) didn’t have his best stuff tonight but he pitched his butt off and competed for us,” BYU coach Mike Littlewood said. “Offensively, we had a lot of selfish at-bats and couldn’t get a big hit. We had way too many strikeouts and poor at-bats.”The Cougars took the initial lead when Brock Hale led off with a short-hop double off the left field wall and scored on Nate Favero’s single to right field in the second inning.In the third frame, Keaton Kringlen made the catch in left field for out number two on a sacrifice fly which gave Portland a 2-1 lead. Kringlen then threw to second on an appeal when the Pilot runner left early on the tag to complete an inning-ending double play.BYU regained the lead at 3-2 in the fourth when the Pilot shortstop’s rushed throwing error allowed Kringlen and Jake Brown, who had doubled, to score.That lead was short-lived when UP’s Hawken hammered his homer to left. Then, Lopez’s dinger in the sixth gave the Pilots a 4-3 lead.The two teams play the second of a three-game series on Friday evening. Robert Lovelllast_img read more

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