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first_imgIdentity, quantity and seasonal variation in recruiting invertebrate larvae were investigated at Signy Island, Antarctica. Nine settlement panels were deployed at each of three sites at depths ranging between five and 25 m over a two year experimental period. Longer-term community development was followed using three panels continuously immersed for up to 21 months at each site, with monthly photographs taken in situ. Shorter-term variations in recruitment were studied by regular replacement of triplicate panels, which enabled the measurement of seasonality of recruitment onto artificial substrata in Antarctica, for the first time. Cyclostomatid and cheilostomatid bryozoans, and spirorbinid polychaetes were the dominant colonising taxa both in terms of numbers and area covered. Very low rates of colonisation were observed: <2% of the panels at 5 m, and <6% of the panel areas at 25 m, were covered after 15 months. Whilst little seasonality of recruitment was observed in spirorbinids, that of cheilostomatid bryozoans showed a significant peak between June and February. Successful recuitment levels of colonising taxa suggested seasonal and interannual variation, although not conclusively. Measurement of growth of individual bryozoan colonies was assessed by image analysis of the in situ monthly photographs. Mean growth ranging between 1.7 mm2 (Lacerna eatoni) and 7.1 mm2 (Arachnopusia inchoata) per month were recorded. There was considerable inter- and intra-specific variation of growth of the encrusting cheilostomatid species investigated and this is the first report of such measurements having been made in Antarctica.last_img read more

first_imgMacaroni penguins are the main avian consumer of Antarctic krill in the vicinity of South Georgia. The largest breeding colonies occur on small offshore islands to the northwest of the main island. To delimit the foraging range of penguins from these colonies during the chick-rearing period, we used a series of ship-based survey transects to estimate their distribution and abundance. The survey transects were positioned so as to radiate from a point close to those islands with the largest colonies. Spatial and temporal variations within the data are examined. Penguins were mostly over the continental shelf in water less than 350 m depth and with more than 70% of birds at distances less than 40 km from the main breeding site. To model the observed distribution of penguins, a theoretical at-sea distribution is developed together with a ‘potential foraging footprint’. The results are compared with those from previous models based solely on the use of foraging trip duration and at-sea activity budgets. The foraging ‘footprint’ is probably the best basis currently available for assessing the nature of interactions between macaroni penguins and the commercial fisheries for krill.last_img read more

first_imgAs part of the Antarctic Digital Magnetic Mapping Project (ADMAP) workers from VNIIOkeangeologia (Russia), the British Antarctic Survey (UK) and the Naval Research Laboratory (USA) have brought together almost all of the available magnetic data in the area 0-120degreesW, 60-90degreesS. The final map covers the whole Weddell Sea and adjacent land areas, the Antarctic Peninsula and the seas to the west, an area comparable in size with that of the USA. This paper describes the methods used during the compilation of the map and reviews briefly some of the main features shown on it. Distinct magnetic provinces are associated with Precambrian rocks of the East Antarctic craton, highly extended continental crust in the Weddell Sea embayment, the arc batholith of the Antarctic Peninsula, and oceanic crust of the northern Weddell Sea, which was created as a direct consequence of South America-Antarctica plate motion and oceanic crust generated at the Pacific-Antarctic ridge. The magnetic anomaly map thus provides an overview of the fragmentation of south-western Gondwana and the tectonic development of the Weddell Sea sector of Antarctica.last_img read more

first_imgA data-driven physical model of the energetic electrons in the Earth’s radiation belts, called the Radiation Belt Environment (RBE) model, has been developed to understand Earth’s radiation belt dynamics and to predict the radiation conditions found there. This model calculates radiation belt electron fluxes from 10 keV to 6 MeV in the inner magnetosphere. It takes into account the realistic, time-varying magnetic field and considers effects of wave-particle interactions with whistler mode chorus waves. The storm on 23–27 October 2002 is simulated and the temporal evolutions of the radial and pitch angle distributions of energetic electrons are examined. The calculated electron fluxes agree very well with particle data from the low-orbit SAMPEX and LANL geosynchronous satellites, when the wave-particle interactions are taken into account during storm recovery. Flux increases begin near the plasmapause and then diffuse outward to higher L shells, consistent with previous findings from statistical studies. A simplified version of the RBE model is now running in real time to provide nowcasting of the radiation belt environment. With further improvements and refinements, this model will have important value in both scientific and space weather applicationslast_img read more

We perform two superposed epoch analyses of the auroral evolution during substorms using the FUV instrument on the Imager for Magnetopause-to-Aurora Global Explorer ( IMAGE) spacecraft. The larger of the two studies includes nearly 2000 substorms. We subdivide the substorms by onset latitude, a measure of the open magnetic flux in the magnetosphere, and determine average auroral images before and after substorm onset, for both electron and proton aurora. Our results indicate that substorms are more intense in terms of auroral brightness when the open flux content of the magnetosphere is larger, and that magnetic flux closure is more significant. The increase in auroral brightness at onset is larger for electrons than protons. We also show that there is a dawn-dusk offset in the location of the electron and proton aurora that mirrors the relative locations of the region 1 and region 2 current systems. Superposed epoch analyses of the solar wind, interplanetary magnetic field, and geomagnetic indices for the substorms under study indicate that dayside reconnection is expected to occur at a faster rate prior to low latitude onsets, but also that the ring current is enhanced for these events. read more

first_imgWe study the dynamics of dimethylsulphide (DMS) and dimethylsulphoniopropionate (DMSP) using the global ocean biogeochemistry model PlankTOM5, which includes three phytoplankton and two zooplankton functional types (PFTs). We present a fully prognostic DMS module describing intracellular particulate DMSP (DMSPp) production, concentrations of dissolved DMSP (DMSPd), and DMS production and consumption. The model produces DMS fields that compare reasonably well with the observed annual mean DMS fields, zonal mean DMS concentrations, and its seasonal cycle. Modeled ecosystem composition and modeled total chlorophyll influenced mean DMS concentrations and DMS seasonality at mid- and high latitudes, but did not control the seasonal cycle in the tropics. The introduction of a direct, irradiation-dependent DMS production term (exudation) in the model improved the match between modeled and observed DMS seasonality, but deteriorated simulated zonal mean concentrations. In PlankTOM5, exudation was found to be most important for DMS seasonality in the tropics, and a variable DMSP cell quota as a function of light and nutrient stress was more important than a PFT-specific minimal DMSPp cell quota. The results suggest that DMS seasonality in the low latitudes is mostly driven by light. The agreement between model and data for DMS, DMSPp, and DMSPd is reasonable at the Bermuda Atlantic Time Series Station, where the summer paradox is observed.last_img read more

first_imgThe presence of ice shelf basal channels has been noted in a number of Antarctic and Greenland ice shelves, but their impact on basal melting is not fully understood. Here we use the Massachusetts Institute of Technology general circulation model to investigate the effect of ice-shelf basal channels on oceanic melt rate for an idealised ice shelf resembling the floating tongue of Petermann Glacier in Greenland. The introduction of basal channels prevents the formation of a single geostrophically balanced boundary current; instead the flow is diverted up the right-hand (Coriolis-favoured) side of each channel, with a return flow in the opposite direction on the lefthand side. As the prescribed number of basal channels is increased the mean basal melt rate decreases, in agreement with previous studies. For a small number of relatively wide channels the sub-ice flow is found to be a largely geostrophic horizontal circulation. The reduction in melt rate is then caused by an increase in the relative contribution of weakly-melting channel crests and keels. For a larger number of relatively narrow channels, the sub-ice flow changes to a vertical overturning circulation. This change in circulation results in a weaker sensitivity of melt rates to channel size. The transition between the two regimes is governed by the Rossby radius of deformation. Our results explain why basal channels play an important role in regulating basal melting, increasing the stability of ice shelves.last_img read more

first_imgThe Southern Ocean archipelago, the South Orkney Islands (SOI), became the world’s first entirely high seas marine protected area (MPA) in 2010. The SOI continental shelf (~44 000 km2), was less than half covered by grounded ice sheet during glaciations, is biologically rich and a key area of both sea surface warming and sea-ice losses. Little was known of the carbon cycle there, but recent work showed it was a very important site of carbon immobilization (net annual carbon accumulation) by benthos, one of the few demonstrable negative feedbacks to climate change. Carbon immobilization by SOI bryozoans was higher, per species, unit area and ice-free day, than anywhere-else polar. Here, we investigate why carbon immobilization has been so high at SOI, and whether this is due to high density, longevity or high annual production in six study species of bryozoans (benthic suspension feeders). We compared benthic carbon immobilization across major regions around West Antarctica with sea-ice and primary production, from remotely sensed and directly sampled sources. Lowest carbon immobilization was at the northernmost study regions (South Georgia) and southernmost Amundsen Sea. However, data standardized for age and density showed that only SOI was anomalous (high). High immobilization at SOI was due to very high annual production of bryozoans (rather than high densities or longevity), which were 2x, 3x and 5x higher than on the Bellingshausen, South Georgia and Amundsen shelves, respectively. We found that carbon immobilization correlated to the duration (but not peak or integrated biomass) of phytoplankton blooms, both in directly sampled, local scale data and across regions using remote-sensed data. The long bloom at SOI seems to drive considerable carbon immobilization, but sea-ice losses across West Antarctica mean that significant carbon sinks and negative feedbacks to climate change could also develop in the Bellingshausen and Amundsen seas.last_img read more

first_imgA filamentous benthic cyanobacteria strain isolated from a tropical man-made pond in Malaysia was characterised using combined phenotypic and genetic approaches. Morphological and ultrastructural observations were performed together with growth measurements. Cell dimensions, thylakoid arrangement and apical cell shape with aerotopes were consistent with the description of Pseudanabaena amphigranulata (Goor) Anagnostidis. Molecular characterisation of the16S rRNA gene gave 94% pairwise sequence identity with Pseudanabaena sp. PCC 6802,which corresponds to the genus identification threshold value while also suggesting that the strain is distinctly different to the species of Pseudanabaena currently represented in available databases. The strain showed identical 16S-23S ITS configuration with other strains of Pseudanabaena apart from having a larger spacer region. Cultures of the strain were exposed to various temperature and photoperiod treatments and harvested at exponential phase in order to examine phenotypic plasticity. Significant relationships between environmental conditions and morphological characteristics (cell dimensions and shape) were identified for the first time within the genus Pseudanabaena. The maximum cell length (5.7 ± 0.07 μm) was observed at 25 °C under 12:12 light to dark, while the greatest cell width (3.2 ± 0.11 μm) was also observed at 25 °C but under 16:8 light to dark. The strain showed high plasticity in cell dimensions and shape under different temperature and photoperiod treatments, with25 °C under 12:12 light to dark providing the optimal conditions for its growth.last_img read more

first_img FacebookTwitterLinkedInEmailSALT LAKE CITY – The Utah baseball team hosts BYU in a midweek contest on Tuesday, April 3, at 6:00 p.m. MT. The game will be televised by the Pac-12 Networks.The contest is the second of four that the Utes and Cougars will play this season. Utah dropped the first game back on March 20, 7-6 in 10 innings. The Utes rallied to tie the game in the ninth inning with four runs to push the contest to extras. The remaining two games are on Tuesday, April 24 in Provo and Tuesday, May 8 in Salt Lake City.The overall winner of the four contests will earn three points towards the Deseret First Duel rivalry series. Utah leads 18.5-10.5 with women’s tennis, softball and baseball remaining for nine total points. Utah has scored points this year in football, women’s gymnastics, men’s and women’s swimming and diving, men’s tennis and women’s soccer.The Utes are coming off a Pac-12 series win over Oregon State, which came into the weekend ranked No. 1 in the nation. Utah is 6-7 in its last 13 games after starting the year 0-13.Utah (6-20, 3-3 Pac-12) is fifth in the Pac-12 in batting average (.267) and hits (240). The Utes are tied for second in the league in stolen bases (26) and tied for third in triples (7). Utah leads the Pac-12 in double plays (24), is tied for second in assists (269) and is fourth in fielding percentage (.976). The Utes are first in the league with nine pickoffs.DaShawn Keirsey, Jr., is on a 12-game hitting streak and is seventh in the Pac-12 in batting average (.367), tied for second in doubles (10), leads the league in doubles per game (0.48) and is 11th in slugging percentage (.532). Wade Gulden is tied for fourth in the league in triples (3). Oliver Dunn and Chandler Anderson are tied for seventh in the Pac-12 with five stolen bases. Dunn is tied for third in the league with 19 double plays and 70 assists. Trenton Stoltz is third in the Pac-12 with 15 appearances. Brett Brocoff is one of seven pitchers who has not allowed a home run this year.BYU is 2-2 in its last four games, dropping two out of three to Pepperdine over the weekend. April 2, 2018 /Sports News – Local Utah Baseball Hosts BYU on Tuesday Written bycenter_img Robert Lovelllast_img read more