Benthic microbial activity in an Antarctic coastal sediment at Signy Island, South Orkney Islands

first_imgMicrobial activity in a marine sediment in Factory Cove, Signy Island (60°43′S, 45°38′W), South Orkney Islands in the maritime Antarctic was examined during December 1987 and January 1988. The sediment was bioturbated by a dense amphipod population in the surface layer but oxygen penetrated to a depth of only 1·7 mm. The top 1 cm was light coloured and contained negligible concentrations of acid-volatile sulphides. Below 1 cm the sediment was black and contained abundant sulphides. Sulphate reduction rates averaged 6·87 × 10−1 μmol sulphate cm−2d−1 over the 0–15 cm horizon, equivalent to 1·38 μmol organic carbon oxidized cm−2d−1. Of the sulphate reduced, 60% was to tin-reducible products (including pyrite) and 40% to acid-volatile sulphides. Annual sulphate reduction was at least 250 μmol sulphate cm−2y−1. The sea water temperature varied only between −1·8−1 °C, but the optimum temperature for sulphate reduction was 21 °C. Oxygen uptake by the benthos averaged 5·33 μmol oxygen cm−2d−1, equivalent to 5·33 μmol organic carbon oxidized cm−2d−1. Aerobic respiration accounted for 79% of the organic carbon mineralization and sulphate reduction for 21%.last_img read more

Worldwide atmospheric gravity-wave study in the European sector 1985–1990

first_imgFour campaigns of the Worldwide Atmospheric Gravity-wave Study (WAGS) have taken place in the European sector. On many occasions the onset of auroral activity in the evening and midnight sector, as indicated by EISCAT measurements of the electric field, was associated after a suitable delay with the detection of periodic ionospheric disturbance travelling southward over the U.K. at speeds between 500 and 1000 m s−1. The velocity and wavelength of the TIDs corresponded to large-scale atmospheric gravity-waves. The characteristic periods of the travelling disturbances were similar to the intrinsic time scales of the auroral activity for periods of 40 min or more, but variations on a time scale of 20 min or less were strongly attenuated. The r.m.s. amplitude of the auroral electric field was proportional to the r.m.s. amplitude of the HF Doppler-shift associated with the gravity-wave. The time-lag between the onset of strong auroral activity and the arrival of the travelling disturbance over the U.K. was usually about an hour, suggesting a source region about 2000 km north. Similar levels of activity in the afternoon did not appear to produce strong waves in the far field. This is possibly due to ion-drag in the daytime ionosphere although the effects of the lower sensitivity of the HF Doppler-network during daytime must also be considered.last_img read more

Oligocene and Pliocene interglacial events in the Antarctic Peninsula dated using strontium isotope stratigraphy

first_imgStrontium isotope stratigraphy is used to date two interglacial-marine deposits in the Antarctic Peninsula region. On King George Island, interglacial pectinid-rich sediments in the Low Head Member of the Polonez Cove Formation give a strontium isotope stratigraphy age of 29.0+0.7−0.6 to 29.8+0.8−0.7 Ma (mid-Oligocene), which, in conjunction with previous K–Ar dating of volcanic rocks, indicates a glacial episode in the Antarctic Peninsula between middle Eocene (42.0 ±1.0 Ma) and mid-Oligocene time. In addition, an inter-glacial deposit (Pecten Conglomerate) from tectonically-elevated exposures on Cockburn Island is dated as Pliocene (3.5–5.3 Ma). Published data suggest these latter sediments were deposited under shallow marine conditions, which were warmer than those of present-day Antarctica.last_img read more

Investigations of squid stocks using acoustic survey methods

first_imgAcoustic survey methods are now widely used for stock assessments of finfish, both those with and without swimbladders, but their application to squid stocks has been limited in the past, probably because squid are not particularly strong targets for detection with echosounders. Experience with acoustic stock assessment of krill (Euphausia superba) has revealed that it is possible to survey effectively for a species that is a weaker target than squid; this is partly due to the tendency for krill to form dense aggregations. This paper discusses examples of acoustic studies on different squid species from the South Atlantic (Loligo gahi, Martialia hyadesi) and demonstrates that squid detection is possible in widely differing locations. L. gahi observed during a survey on the Falkland Shelf were shown to have acoustic characteristics in common with smaller organisms which may enable them to be distinguished acoustically from finfish encountered in these waters. When a species has been characterised acoustically, the technique permits rapid surveys of large areas to determine the geographic range of a population, both outside the usual area that can be surveyed using fishing methods and within areas that are inaccessible to nets for some reason.last_img read more

Seabed morphology and the bottom-current pathways around Rosemary Bank seamount, northern Rockall Trough, North Atlantic

first_imgRosemary Bank is a broadly domed and elongate seamount with a diameter of 70 km, occurring in water depths of between 300 and 2300 m, 120 km west of the UK mainland in the northern Rockall Trough. Recent multibeam bathymetry and sub-bottom profiles, together with pre-existing current meter and CTD data, seismic reflection profiles and seabed core samples were examined in order to evaluate past and present bottom-current pathways and processes. The multibeam data image volcanic parasitic cones, concave slide scars and the terraced slopes of the bank. Bottom-current sedimentation is interpreted as producing a drift–moat complex surrounding the entire seamount and including two sediment wave-fields, developed to the west and east of the bank in water depths of 1500–2000 m. The western drift covers an area of over 1000 km2. Sediment waves to the west of the bank are up to 150 m high with wave lengths of 1.5–2 km. Four 100 m deep, 3 km wide, linear depressions, bisect the waves and are interpreted as 25–30 km long extensions of the moat. Seismic reflection profiles show the main phase of drift construction was during the mid-Miocene to Pliocene with the Pliocene to Holocene being an interval of drift maintenance. Cores from sediments draping over and adjacent to the seamount contain sandy and gravelly contourites interbedded with hemipelagites of late Pleistocene to Holocene age. Current meter and CTD data from the western moat indicate Labrador Sea Water flowing northwest, in contrast to the previously assumed anticlockwise circulation pattern around the seamount.last_img read more

The response of ice shelf basal melting to variations in ocean temperature.

first_imgA three-dimensional ocean general circulation model is used to study the response of idealized ice shelves to a series of ocean-warming scenarios. The model predicts that the total ice shelf basal melt increases quadratically as the ocean offshore of the ice front warms. This occurs because the melt rate is proportional to the product of ocean flow speed and temperature in the mixed layer directly beneath the ice shelf, both of which are found to increase linearly with ocean warming. The behavior of this complex primitive equation model can be described surprisingly well with recourse to an idealized reduced system of equations, and it is shown that this system supports a melt rate response to warming that is generally quadratic in nature. This study confirms and unifies several previous examinations of the relation between melt rate and ocean temperature but disagrees with other results, particularly the claim that a single melt rate sensitivity to warming is universally valid. The hypothesized warming does not necessarily require a heat input to the ocean, as warmer waters (or larger volumes of “warm” water) may reach ice shelves purely through a shift in ocean circulation. Since ice shelves link the Antarctic Ice Sheet to the climate of the Southern Ocean, this finding of an above-linear rise in ice shelf mass loss as the ocean steadily warms is of significant importance to understanding ice sheet evolution and sea level rise.last_img read more

Ice shelf/ocean interactions under the Amery Ice Shelf: seasonal variability and its effect on marine ice formation

first_imgMarine ice is an important factor in ice shelf stability. An extensive marine ice layer is present under the Amery Ice Shelf (AIS), East Antarctica. This paper documents observations on the seasonal variability of the AIS–ocean interaction beneath its marine ice layer. We focus on data collected during 2002 through a borehole at AM01, 100 km from the ice shelf calving front, and use additional data from two other boreholes to complement the study. At AM01, the top ~20 m of the water column is super–cooled almost year–round, protecting the marine ice layer and promoting frazil ice formation. The mixed layer thickness varies from ~50 m in February to at least 160 m by June, as the water column cools and freshens. High Salinity Shelf Water (HSSW) abruptly arrives at AM01 in June–August as an eddy–like flow. We suggest that the flow characteristics are a result of baroclinic instabilities. In addition, the inflow of HSSW results in a steepening of the isopycnals that enhances the upwelling of Ice Shelf Water. This study documents, for the first time, a seasonal signal in the formation of marine ice under the AIS. Our results highlight the vulnerability of the marine ice layer to ocean variability with potential consequences for the overall ice shelf mass balance.last_img read more

Assessing the effectiveness of specially protected areas for conservation of Antarctica’s botanical diversity

first_imgVegetation is sparsely distributed over Antarctica’s ice-free ground, and distinct plant communities are present in each of the continent’s 15 recently identified Antarctic Conservation Biogeographic Regions (ACBRs). With rapidly increasing human activity in Antarctica, terrestrial plant communities are at risk of damage or destruction by trampling, overland transport and infrastructure construction, and the impacts of anthropogenically introduced species, as well as uncontrollable pressures such as fur seal activity and climate change. Under the Protocol on Environmental Protection to the Antarctic Treaty, the conservation of plant communities can be enacted and facilitated through the designation of Antarctic Specially Protected Areas (ASPAs). In this study we examined the distribution within the 15 ACBRs of the 33 ASPAs whose explicit purpose includes protecting macroscopic terrestrial flora. Large omissions in the protection of Antarctic botanical diversity were found, with no protection of plant communities in six ACBRs and, in a further six, less than 0.4% of the ACBR area was included within an ASPA protecting vegetation. We completed the first normalised difference vegetation index (NDVI) satellite remote sensing survey to provide baseline data on the extent of vegetation cover in all ASPAs designated for plant protection in Antarctica. Protected vegetation cover within the 33 ASPAs totalled 16.1 km2 for the entire Antarctic continent, with over half of this within a single protected area. Over 96% of the protected vegetation was contained within two ACBRs, which together contribute only 7.8% of the continent’s ice-free ground. We conclude that Antarctic botanical diversity is clearly inadequately protected, and call for systematic designation of ASPAs protecting plant communities across by the Antarctic Treaty Consultative Parties, the members of the governing body of the continentlast_img read more

Unarmed man fatally shot by police honored at NBA game: ‘These tragedies have to stop’

first_img FacebookTwitterLinkedInEmailPaul Kitagaki Jr./Sacramento Bee/TNS via Getty Images(SACRAMENTO) — The Sacramento Kings took the home floor Sunday and donned T-shirts honoring the unarmed 22-year-old who was shot and killed by police last week.On the front of the shirts read “ACCOUNTABILITY. WE ARE ONE.” On the back, there was a hashtag — #StephonClark — the name of the man who was killed March 18 in his grandmother’s backyard.During a first-quarter timeout, a unified public service announcement from players from the Kings and the opposing team, the Boston Celtics, played on the JumboTron at Gold 1 Center in Sacramento.In it, the players, over soft music, deliver various messages over the 30-second clip: “There must be accountability.”“We won’t shut up and dribble.”“These tragedies have to stop.”Clark was killed after officers responded to a 911 call of a man in a hoodie breaking car windows and hiding in a backyard in the 7500 block of 29th Street.When the officers encountered Clark there, according to released body cam footage, they believed Clark was in possession of a “toolbar,” according to police accounts.Officers said Clark motioned toward them and one of them can be heard yelling: “Show me your hands… Gun, gun, gun.”After both officers fired 20 shots, fatally wounding Clark, investigators recovered a cell phone near Clark’s body but no weapons.Since the shooting, protestors have taken to the streets to call for change.On Thursday, protesters formed a human wall and shouted “Shut it down!” stalling a game between the Kings and the Atlanta Hawks and preventing fans from entering the arena.More protests are being planned. Longtime community activist Berry Accius, 40, who moved to the state capital 12 years ago from Long Island, New York, told ABC News that on Tuesday at 5 p.m. there will be a rally to “blackout” City Hall.“People will be wearing black to represent the anti-blackness that has been shown out here in Sacramento,” he said.Through a family spokesman, Clark’s family declined an interview. His brother, Stevante Clark, and the spokesman, however, said Benjamin Crump — who represented the family of Trayvon Martin, 17, who was fatally shot by a neighborhood watch volunteer in Florida in 2012 — would serve as an attorney for the Clark family.Copyright © 2018, ABC Radio. All rights reserved. March 25, 2018 /Sports News – National Unarmed man fatally shot by police honored at NBA game: ‘These tragedies have to stop’ Beau Lundcenter_img Written bylast_img read more

George Steinbrenner headlines ten-man ballot for Baseball Hall of Fame’s Today’s Game Era committee

first_img Beau Lund Written by November 6, 2018 /Sports News – National George Steinbrenner headlines ten-man ballot for Baseball Hall of Fame’s Today’s Game Era committeecenter_img FacebookTwitterLinkedInEmailiStock/Thinkstock(NEW YORK) — Legendary former New York Yankees owner George Steinbrenner headlines a list of ten larger-than-life figures eligible for induction into the Baseball Hall of Fame next month, with their selection to be overseen by the Today’s Game Era committee.Also on the list are former managers Davey Johnson, Lou Piniella and Charlie Manuel, and a group of players that includes Harold Baines, Albert Belle, Joe Carter, Will Clark, Orel Hershiser, and Lee Smith. The 16-person committee is responsible for choosing candidates who were involved in the sport from 1998 and the present. The committee will meet on December 9 at Major League Baseball’s winter meetings in Las Vegas. Any candidate who receives 75 percent of the vote will be inducted at Cooperstown next July, alongside the players chosen from the standard ballot in January. The Today’s Game Era committee last met two years ago, choosing former MLB commissioner Bud Selig and former Atlanta Braves executive John Schuerholz for induction. Each of the individuals up for consideration this year were considered then, but none received more than half of the vote.Copyright © 2018, ABC Radio. All rights reserved.last_img read more