Estudio de la Edad en una población virginal de Notothenia gibberifrons (Pisces:Nototheniidae) de Bahia South, Antartica

first_imgThe age of individuals Notothenia gibberifrons Lönnberg was determined for a sample from an unexploited population collected at South Bay ,Palmer Archipelago. Elsewhere in the Antartic this species has been to commercial – scale fishing and so it is difficult to obtain the age structure of an undisturbed population.last_img

Age and correlation of volcanism in central Livingston Island, South Shetland Islands: K-Ar and geochemical constraints

first_imgVolcanic sequences in central Livingston Island can be divided into two broad groups. The older group consists of basalt-dacite lavas, clastic rocks and associated hypabyssal intrusions. The lavas are lithologically and compositionally similar to other pre-Pliocene, volcanic arc lavas in the South Shetland Islands. The outcrops vary from relatively fresh (at Cape Shirreff, Hannah Point and Siddons Point) to indurated and pervasively altered (at Mount Bowles, Burdick Peak and Hurd Peninsula). Samples from the fresh outcrops yielded Late Cretaceous ages for eruption or intrusion, ranging from 90.2 ± 5.6 Ma at Cape Shirreff, to 73.0 ± 2.3 at Siddons Point. Chemical analyses of the lavas suggest that the sequences at these two outcrops can probably be correlated stratigraphically with the Byers Group and Coppermine Formation, respectively. Two samples from Hannah Point yielded conflicting ages of 87.9 ± 2.6 Ma and 67.5 ± 2.5 Ma from the centre and top of the sequence, respectively. The stratigraphical affinities of the Hannah Point sequence cannot yet be determined unambiguously but it is unlikely to be part of the Byers Group. All of the samples from the altered outcrops (which correspond to the Mount Bowles Formation) yielded Eocene-Oligocene K-Ar ages (44.4 to 35.0 Ma), interpreted as reset ages related to the emplacement and cooling of a nearby Eocene tonalite pluton responsible for much of the alteration, and also dated in this study (43.3 ± 2.8 Ma). A Cretaceous eruptive age (possibly Late Cretaceous) for the altered outcrops is likely but cannot yet be proven. By contrast, the younger group consists of degraded basalt lava flows, tuff cone and tuff ring remnants, which are part of the Inott Point Formation. The lavas are very fresh and Pleistocene or Recent in age (≤ 1 Ma). They are compositionally distinctive and are indistinguishable from supra-subduction alkali basalts preserved elsewhere in Livingston, Greenwich and Penguin islands.last_img read more

Monitoring a marine ecosystem using responses of upper trophic level predators

first_img1 This study examined the changing status of the marine ecosystem at the island of South Georgia (Southern Ocean) using up to 27 variables measured over 22 years from three upper trophic level predators that specialize in foraging upon krill (Eupuasia superba Dana). These variables included population size, breeding performance, offspring growth rate, foraging behaviour and diet. A method was developed for reducing these multivariate time-series to a single vector, called a combined standardized index (CSI).2 Sensitivity analyses showed that missing values had a large effect upon the accuracy of the CSI but this effect was reduced if the individual variables were highly correlated. The level of correlation and proportion of missing values within the empirical data set were within the acceptable range. Individual variables had widely varying influence upon the CSI but, in general, those with longer time-series had the greatest influence.3 Principal components analysis showed that variables representing offspring growth tended to explain the greatest proportion of the variability in the CSI and this was followed by variables representing diet.4 There were 3 years in which the CSI showed extreme and significantly low values. There was a significant non-linear functional response (similar to the Holling Type II functional response) between the overall CSI and krill biomass and a similar relationship existed when the CSI was calculated for each species individually.5 Separate analysis of variables that were likely to be representative of changing population size showed the presence of a significant decline between 1977 and 1998. There was no trend in the CSI from variables representative of foraging conditions during the summer breeding season. The study has shown that the marine ecosystem at South Georgia shows acute but transient variability that is amplified in the response of upper trophic-level predators. There is less certainty that trends in populations are a consequence of shifts in the degree to which the ecosystem can support krill-feeding seals and penguins.last_img read more

Latitudinal patterns of diversity and abundance in North Atlantic intertidal boulder-fields

first_imgIn order to study taxon richness, biodiversity and abundance patterns in the North Atlantic from temperate latitudes through Arctic to high Arctic latitudes, we recorded the faunas (at ELWS level) colonizing 20 cobbles from three sites at each of seven boulder-field localities (south-west England, 50°N; Wales, 51°N; west Scotland, 56°N; Iceland, 64°N; Tromsø, 70°N; Svalbard, 77°N, 79°N). Inverse correlations were found between latitude and all measures of richness (species, orders, and phyla numbers) and biodiversity (S–W, P). However, these correlations were driven mostly by the consistently impoverished Arctic sites; an even cline of decreasing diversity from south to north did not exist. Multidimensional scaling revealed two communities, temperate–subarctic species-rich and high arctic species-poor. Evenness as measured by Pielou’s index was similar across all latitudes. Abundance data exhibited a similar trend to the species richness and diversity data with a significant negative correlation with latitude, but when Arctic data were excluded the correlation vanished.last_img read more

Ice stream retreat following the LGM and onset of the west Greenland current in Uummannaq Trough, west Greenland

first_imgThe deglacial history and oceanography of Uummannaq Trough, central West Greenland continental shelf, was investigated using foraminiferal, sedimentological, and bathymetric records together with a radiocarbon chronology, providing a timeline for the retreat of glacial ice after the Last Glacial Maximum (LGM). To map ice stream retreat, data were collected from cores from the outer (JR175-VC45 and JR175-VC43) and inner (JR175-VC42) Uummannaq Trough. A large ice stream, fed by confluent glaciers draining the interior of the Greenland Ice Sheet, extended across the outer shelf during the LGM and was in retreat by 15.0 cal kyr BP. Foraminiferal data indicate that the ‘warm’ West Greenland Current (WGC) was established prior to 14.0 cal kyr BP, which is the hitherto earliest record of Atlantic Water found on the West Greenland shelf. For each of the cores, foraminifera indicate that ice sheet retreat was followed quickly by incursion of the WGC, suggesting that the warm water may have enhanced ice retreat. Prior to the Younger Dryas cold event, the radiocarbon chronology indicates that the ice sheet retreated to the mid-shelf, where it subsequently stabilised and formed a large grounding-zone wedge (GZW). After the Younger Dryas, around 11.5 cal kyr BP, the ice retreated rapidly from the GZW and into the fjords.last_img read more

Positive trend in the Antarctic sea ice cover and associated changes in surface temperature

first_imgThe Antarctic sea ice extent has been slowly increasing contrary to expected trends due to global warming and results from coupled climate models. After a record high extent in 2012 the extent was even higher in 2014 when the magnitude exceeded 20 × 106 km2 for the first time during the satellite era. The positive trend is confirmed with newly reprocessed sea ice data that addressed inconsistency issues in the time series. The variability in sea ice extent and ice area was studied alongside surface ice temperature for the 34-yr period starting in 1981, and the results of the analysis show a strong correlation of −0.94 during the growth season and −0.86 during the melt season. The correlation coefficients are even stronger with a one-month lag in surface temperature at −0.96 during the growth season and −0.98 during the melt season, suggesting that the trend in sea ice cover is strongly influenced by the trend in surface temperature. The correlation with atmospheric circulation as represented by the southern annular mode (SAM) index appears to be relatively weak. A case study comparing the record high in 2014 with a relatively low ice extent in 2015 also shows strong sensitivity to changes in surface temperature. The results suggest that the positive trend is a consequence of the spatial variability of global trends in surface temperature and that the ability of current climate models to forecast sea ice trend can be improved through better performance in reproducing observed surface temperatures in the Antarctic region.last_img read more

Unexpected absence of island endemics: Long-distance dispersal in higher latitude sub-Antarctic Siphonaria (Gastropoda: Euthyneura) species

first_imgAim We assess biogeographical patterns, population structure and the range of species in the pulmonate genus Siphonaria across the sub‐Antarctic. We hypothesized that locally endemic cryptic species will be found across the distribution of these direct‐developing limpets in the sub‐Antarctic. Location The sub‐Antarctic coasts of the Southern Ocean including South America, the Falkland/Malvinas, South Georgia, Kerguelen and Macquarie Islands. Methods Multi‐locus phylogenetic reconstructions, mtDNA time‐calibrated divergence time estimations and population‐based analyses of Siphonaria populations were used at the scale of the Southern Ocean. Results We resolve two widely distributed lineages of Siphonaria (S. lateralis and S. fuegiensis) across the sub‐Antarctic. MtDNA divergence time estimates suggest that they were separated around 4.0 Ma (3.0 to 8.0 Ma). Subsequently both species followed different evolutionary pathways across their distributions. Low levels of genetic diversity characterize the populations of both species, reflecting the role of Quaternary glacial cycles during their respective demographic histories, suggesting high levels of dispersal among geographically distant localities. Main conclusions Siphonaria lateralis and S. fuegiensis constitute sister and broadly co‐distributed species across the sub‐Antarctic. Unexpected transoceanic similarities and low levels of genetic diversity in both these direct‐developing species imply recurrent recolonization processes through long‐distance dispersal to isolated sub‐Antarctic islands. For such groups of Southern Ocean invertebrates, rafting may be more effective for long‐distance dispersal than a free‐living planktotrophic larval stage. This biogeographical model may explain why many marine species lacking a dispersal phase exhibit broad distributions, low genetic diversity and low population structure over thousands of kilometres.last_img read more

Scoreboard roundup — 5/10/18

first_img Written by NATIONAL HOCKEY LEAGUE PLAYOFFSWinnipeg 5, Nashville 1 May 11, 2018 /Sports News – National Scoreboard roundup — 5/10/18 AMERICAN LEAGUEBoston 5, N.Y. Yankees 4Baltimore 11, Kansas City 6                                                   Seattle 9, Toronto 3L.A. Angels 7, Minnesota 4 NATIONAL LEAGUEPhiladelphia 6, San Francisco 3Atlanta 9, Miami 2Milwaukee 5, Colorado 2Washington 2, Arizona 1, 11 InningsSt. Louis 2, San Diego 1Cincinnati 4, L.A. Dodgers 1 FacebookTwitterLinkedInEmailiStock/Thinkstock(NEW YORK) — Here are the scores from Thursday’s sports events:AMERICAN LEAGUEBoston 5, N.Y. Yankees 4Baltimore 11, Kansas City 6    Seattle 9, Toronto 3L.A. Angels 7, Minnesota 4NATIONAL LEAGUEPhiladelphia 6, San Francisco 3Atlanta 9, Miami 2Milwaukee 5, Colorado 2Washington 2, Arizona 1, 11 InningsSt. Louis 2, San Diego 1Cincinnati 4, L.A. Dodgers 1NATIONAL HOCKEY LEAGUE PLAYOFFSWinnipeg 5, Nashville 1Copyright © 2018, ABC Radio. All rights reserved.(NEW YORK) — Here are the scores from Thursday’s sports events: Beau Lundlast_img read more

Dixie State Football Seeks First-Ever Win Against CSU Pueblo Saturday

first_img Brad James Written by FacebookTwitterLinkedInEmailST. GEORGE, Utah-Saturday, Dixie State football commences its season at Colorado State-Pueblo, seeking their first-ever win against the Thunderwolves in program history.CSU-Pueblo comes in as the #14 ranked team in the Division II polls and this is the third game in history between the Thunderwolves and Trailblazers.A Dixie State win would be a tremendous feather in their cap as the Thunderwolves are projected as the Rocky Mountain Athletic Conference favorite per a poll from coaches in the conference.Since going to Division II in 2007, Dixie State is 1-13 in match-ups against foes in the Top 25.A Trailblazers win here would be their first against a ranked opponent since a 38-31 victory over #23 Colorado Mesa in 2016.Dixie State has stumbled out of the blocks traditionally, going 2-10 all-time in season openers as a Division II school. Their last season-opening win came in 2016, when they downed New Mexico Highlands 21-14.The Trailblazers will be led by junior tailback Sei-J Lauago (803 rushing yards, 5 TD’s in 2017 in just eight games) and redshirt junior receiver Kasey Allison (39 rec, 580 yards, 4 TD’s in 2017) on offense.Defensively, they are paced by junior safety Mike Jones (84 tackles, five pass breakups, four forced fumbles, two tackles for a loss and 1.5 sacks).Other defensive stalwarts include senior safety Trayvon Watson (69 tackles, six pass breakups, four interceptions, two fumble recoveries) and senior defensive lineman Remington Kelly (58 tackles, nine tackles for a loss, nine quarterback hurries, 3.5 sacks and a 46-yard fumble return for a touchdown in 2017).The Thunderwolves are paced by quarterback Brandon Edwards, who has tossed for 732 yards, 4 touchdowns and three interceptions in his career.The CSU-Pueblo running game is their strong point as senior Marche Dennard (1,083 career rushing yards, 17 touchdowns) and junior Austin Micci (694 career rushing yards, eight touchdowns).Ammon Johnson is the Thunderwolves’ returning leading receiver, having posted 547 receiving yards and three touchdowns last season in his sophomore campaign. August 30, 2018 /Sports News – Local Dixie State Football Seeks First-Ever Win Against CSU Pueblo Saturday Tags: Brandon Edwards/Colorado State-Pueblo/Division II/Dixie State/Kasey Allison/Mike Jones/Remington Kelly/Sei-J Lauago/Trayvon Watsonlast_img read more

Utah State Men’s/Women’s Cross Country Teams Each Ranked In Top 10

first_img Tags: BYU/New Mexico/Northern Arizona/Sagebrush Invitational/Southern Utah/Utah/Utah State Men’s/Women’s Cross Country/Utah Valley/Weber State FacebookTwitterLinkedInEmailLOGAN, Utah-Information released Monday confirms Utah State men’s and women’s cross country were each ranked in the Top 10 of the NCAA Division I cross country regional rankings.This was released by the U.S. Track and Field and Cross Country Coaches Association.The Aggie women are ranked third in the Mountain Region, with the men currently ranked seventh.The New Mexico women are the top-ranked team in the Mountain Region and in Utah, the BYU women are ranked fourth, the Utah women are sixth, Southern Utah is 10th, Weber State is 11th and Utah Valley, 15th.The top-ranked men’s team in the Mountain Region is Northern Arizona.The Aggies will commence their season September 1 at home with the Sagebrush Invitational. Utah will be on hand to compete against the Aggies as fellow representatives of the Beehive State. August 28, 2018 /Sports News – Local Utah State Men’s/Women’s Cross Country Teams Each Ranked In Top 10 Written by Brad Jameslast_img read more