Electrical resistivity of ice from the Antarctic Peninsula, Antarctica

Georesistivity soundings have been carried out at four sites in the Antarctic Peninsula. The objective of the work was to investigate the electrical behaviour of ice from an area where substantial melting occurs in summer and from contrasting thermal regimes. Electrical measurements made at three sites along a flow line within George VI Ice Shelf reveal that: (a) the resistivity of deep ice is similar to that of other Antarctic ice shelves,(b)the resistivity of the ice-shelf surface, which is affected by the percolation and refreezing of melt water, is similar to that of deep ice and hence the ice is polar in character. A compilation of published resistivities of deep ice from polar regions shows that the range of resistivities is very narrow (0.4 –2.0) x 105 Ω m between –2 and – 29°C, irrespective of the physical setting and history of the ice. Typically, resistivity is within a factor of two of 80 kΩ m at –20° C with an activation energy of 0.22 eV. In contrast, the resistivity of surface ice at Wormald Ice Piedmont, where the ice is at 0°C throughout, is two orders of magnitude higher and falls at the lower end of the range of resistivities for temperate ice. read more

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Late Pleistocene and Holocene glacial history of James Ross Island, Antarctic Peninsula

first_imgStudies of Quaternary glacial stratigraphy and morphology around the Antarctic Peninsula have shown that James Ross Island in the western Weddell Sea probably has the best occurrences of stratigraphic sections with dateable material in the region. The stratigraphy includes sections with indefinite radiocarbon age, and three separate aminozones can be recognized. Except for indications of an early deglaciation around c. 10,000 BP, the field evidence from northern James Ross Island suggests a glacial readvance around 7000 BP. It is concluded that the readvance reflects the combined effects of eustatic sea level rise and Holocene warming, leading to increased precipitation and a positive mass balance. The most recent large-scale deglaciation in the area took place around 6000–5000 BP. This confirms the evidence from lake sediments and moss banks in other parts of the Antarctic Peninsula region, which shows that, in most cases, the initiation of organic deposition took place after c. 6000 BP. The literature on the Holocene glacial and environmental history of the region is reviewed in light of the new field evidence.last_img read more

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An International Plan for Antarctic Subglacial Lake Exploration

first_imgDiscovery of at least 100 subglacial lakes beneath the vast East Antarctic Ice Sheet has focused international attention on the challenges presented by the way we conduct science in such unique and inhospitable settings in an atmosphere of increasingly stringent environmental concerns. Exploration of subglacial environments will require careful and detailed planning, organization, and international cooperation. To this end, the Scientific Committee on Antarctic Research (SCAR) convened an international Group of Specialists (Subglacial Antarctic Lake Exploration Group of Specialists—SALEGOS) to develop a detailed assessment of the needs and critical milestones to be accomplished during the implementation of a subglacial exploration and research program. This paper surveys the progress and recommendations made by SALEGOS since its inception regarding the current state of knowledge of subglacial environments, technological needs and challenges, international management, the portfolio of scientific projects, and “clean” requirements for entry, observatory deployment, and sample retrievallast_img read more

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Moult cycle-related changes in feeding rates of larval krill Meganyctiphanes norvegica and Thysanoessa spp

first_imgKnowledge of crustacean moulting is derived mainly from benthic decapods, which often show profound changes in physiology and behaviour through the moult cycle. In contrast, euphausiids are suggested to be little impaired by moulting, enabling a swarming pelagic life. The aim of this study was to quantify moult cycle-related changes in the feeding activity of 2 euphausiids, Meganyctiphanes norvegica and Thysanoessa spp. Late furcilia larvae and early postlarvae were kept individually over 6 to 7 wk and fed with either a high or low concentration of Artemia salina nauplii or particulate fish food. The intermoult period, similar to9 d for M norvegica and similar to8 d for Thysanoessa spp., increased with body weight, but did not differ with food source. Moulting was partially synchronised, with up to 50 % of the individuals moulting within 48 h of each other. Daily feeding rates on A, salina decreased on the day before moulting, but increased during the next few days with highest values on Days 1 to 3 after moulting. The deviation from the mean feeding rate over the whole moult was more pronounced at the higher food concentration, reaching up to 40 %. Likewise, the defecation volume was reduced on the moulting day and the following day to similar to50 % of the mean, but increased to 180 % of the mean on Day 3 after moulting. Thus, the moult cycle induces significant changes in feeding rates of larval euphausiids with a similar succession of events and intensity as observed in decapods. Feeding rates, extrapolated from spot measurements on a few individuals, are unlikely to represent average values over the whole moult cycle, especially when populations moult synchronously. We propose a protocol to increase the precision of field estimates on feeding rates.last_img read more

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Modeling past atmospheric CO2: results of a challenge

first_imgThe models and concepts used to predict future climate are based on physical laws and information obtained from observations of the past. New paleoclimate records are crucial for a test of our current understanding. The Vostok ice core record [Petit et al., 1999] showed that over the past 420 kyr (1 kyr = 1000 years), Antarctic climate and concentrations of the greenhouse gases carbon dioxide (CO2) and methane (CH4) were tightly coupled. In particular, CO2 seemed to be confined between bounds of about 180 ppmv (parts per million by volume) in glacial periods and 280 ppmv in interglacials; both gases rose and fell with climate as the Earth passed through four glacial/interglacial cycles.last_img read more

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The Moray Firth directed squid fishery

first_imgIn summer 2003, the usually small directed fishery for the squid Loligo forbesi in the Moray Firth off the northeast coast of Scotland (UK) generated unusually high catches. This fishery, which targets small squid close inshore, ultimately involved over 65 boats. The present short paper reviews the history of this fishery, examines trends over the last 35 years and possible future management issues are briefly reviewed.last_img

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Is vertical migration in Antarctic krill (Euphausia superba) influenced by an underlying circadian rhythm?

first_imgAntarctic krill (Euphausia superba) is a keystone species in the southern ocean ecosystem where it is the main consumer of phytoplankton and constitutes the main food item of many higher predators. Both food and predators are most abundant at the surface, thus krill hide in the depth of the ocean during the day and migrate to the upper layers at night, to feed at a time when the predatory risk is lowest. Although the functional significance of this diel vertical migration (DVM) is clear and its modulation by environmental factors has been described, the involvement of an endogenous circadian clock in this behaviour is as yet not fully resolved. We have analysed the circadian behaviour of Euphausia superba in a laboratory setting and here we present the first description of locomotor activity rhythms for this species. Our results are in agreement with the hypothesis that the circadian clock plays a key role in DVM. They also suggest that the interplay between food availability, social cues and the light:dark cycle acts as the predominant Zeitgeber for DVM in this species.last_img read more

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Effects of simulated light regimes on gene expression in Antarctic krill (Euphausia superba Dana)

first_imgA change in photoperiod has been implicated in triggering a transition from an active to a quiescent state in Antarctic krill. We examined this process at the molecular level, to identify processes that are affected when passing a photoperiodic threshold. Antarctic krill captured in the austral autumn were divided into two groups and immediately incubated either under a photoperiod of 12 h light:12 h darkness (LID), simulating the natural light cycle, or in continuous darkness (DID), simulating winter. All other conditions were kept identical between incubations. After 7 days of adaptation, krill were sampled every 4h over a 24h period and frozen. Total RNA was extracted from the heads and pooled to construct a suppression subtractive hybridisation library. Differentially expressed sequences were identified and annotated into functional categories through database sequence matching. We found a difference in gene expression between LD and DD krill, with LID krill expressing more genes involved in functions such as metabolism, motor activity, protein binding and various other cellular activities. Eleven of these genes were examined further with quantitative polymerase chain reaction analyses, which revealed that expression levels were significantly higher in LD krill. The genes affected by simulated photoperiodic change are consistent with known features of quiescence, such as a slowing of moult rate, a lowering of activity levels and a reduction in metabolic rate. The expression of proteases involved in apolysis, where the old cuticle separates from the epidermis, showed particular sensitivity to photoperiod and point to the mechanism by which moult rate is adjusted seasonally. Our results show that key processes are already responding at the molecular level after just 7 days of exposure to a changed photoperiodic cycle. We propose that krill switch rapidly between active and quiescent states and that the photoperiodic cycle plays a key role in this process. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.last_img read more

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The Twentieth Century Reanalysis Project

first_imgThe Twentieth Century Reanalysis (20CR) project is an international effort to produce a comprehensive global atmospheric circulation dataset spanning the twentieth century, assimilating only surface pressure reports and using observed monthly sea-surface temperature and sea-ice distributions as boundary conditions. It is chiefly motivated by a need to provide an observational dataset with quantified uncertainties for validations of climate model simulations of the twentieth century on all time-scales, with emphasis on the statistics of daily weather. It uses an Ensemble Kalman Filter data assimilation method with background ‘first guess’ fields supplied by an ensemble of forecasts from a global numerical weather prediction model. This directly yields a global analysis every 6 hours as the most likely state of the atmosphere, and also an uncertainty estimate of that analysis. The 20CR dataset provides the first estimates of global tropospheric variability, and of the dataset’s time-varying quality, from 1871 to the present at 6-hourly temporal and 2° spatial resolutions. Intercomparisons with independent radiosonde data indicate that the reanalyses are generally of high quality. The quality in the extratropical Northern Hemisphere throughout the century is similar to that of current three-day operational NWP forecasts. Intercomparisons over the second half-century of these surface-based reanalyses with other reanalyses that also make use of upper-air and satellite data are equally encouraging. It is anticipated that the 20CR dataset will be a valuable resource to the climate research community for both model validations and diagnostic studies. Some surprising results are already evident. For instance, the long-term trends of indices representing the North Atlantic Oscillation, the tropical Pacific Walker Circulation, and the Pacific–North American pattern are weak or non-existent over the full period of record. The long-term trends of zonally averaged precipitation minus evaporation also differ in character from those in climate model simulations of the twentieth century.last_img read more

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The response of the ionosphere-thermosphere system to the August 21, 2017 solar eclipse

first_imgWe simulated the effects of the 21 August 2017 total solar eclipse on the ionosphere‐thermosphere system with the Global Ionosphere Thermosphere Model (GITM). The simulations demonstrate that the horizontal neutral wind modifies the eclipse‐induced reduction in total electron content (TEC), spreading it equatorward and westward of the eclipse path. The neutral wind also affects the neutral temperature and mass density responses through advection and the vertical wind modifies them further through adiabatic heating/cooling and compositional changes. The neutral temperature response lags behind totality by about 35 min, indicating an imbalance between heating and cooling processes during the eclipse, while the ion and electron temperature responses have almost no lag, indicating they are in quasi steady state. Simulated ion temperature and vertical drift responses are weaker than observed by the Millstone Hill Incoherent Scatter Radar, while simulated reductions in electron density and temperature are stronger. The model misses the observed posteclipse enhancement in electron density, which could be due to the lack of a plasmasphere in GITM. The simulated TEC response appears too weak compared to Global Positioning System TEC measurements, but this might be because the model does not include electron content above 550‐km altitude. The simulated response in the neutral wind after the eclipse is too weak compared to Fabry Perot interferometer observations in Cariri, Brazil, which suggests that GITM recovers too quickly after the eclipse. This could be related to GITM heating processes being too strong and electron densities being too high at low latitudes.last_img read more

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