Acoustic discrimination of Southern Ocean zooplankton

first_imgAcoustic surveys in the vicinity of the sub-Antarctic island of South Georgia during a period of exceptionally calm weather revealed the existence of a number of horizontally extensive yet vertically discrete scattering layers in the upper 250 m of the water column. These layers were fished with a Longhurst-Hardy plankton recorder (LHPR) and a multiple-opening 8 m2 rectangular mid-water trawl (RMT8). Analysis of catches suggested that each scattering layer was composed predominantly of a single species (biovolume>95%) of either the euphausiids Euphausia frigida or Thysanöessa macrura, the hyperiid amphipod Themisto gaudichaudii, or the eucalaniid copepod Rhincalanus gigas. Instrumentation on the nets allowed their trajectories to be reconstructed precisely, and thus catch data to be related directly to the corresponding acoustic signals. Discriminant function analysis of differences between mean volume backscattering strength at 38, 120 and 200 kHz separated echoes originating from each of the dominant scattering layers, and other signals identified as originating from Antarctic krill (Euphausia superba), with an overall correct classification rate of 77%. Using echo intensity data alone, gathered using hardware commonly employed for fishery acoustics, it is therefore possible to discriminate in situ between several zooplanktonic taxa, taxa which in some instances exhibit similar gross morphological characteristics and have overlapping length– frequency distributions. Acoustic signals from the mysid Antarctomysis maxima could also be discriminated once information on target distribution was considered, highlighting the value of incorporating multiple descriptors of echo characteristics into signal identification procedures. The ability to discriminate acoustically between zooplankton taxa could be applied to provide improved acoustic estimates of species abundance, and to enhance field studies of zooplankton ecology, distribution and species interactions.last_img read more

Trace metals in the Antarctic soft-shelled clam Laternula elliptica: implications for metal pollution from Antarctic research stations

first_imgThe concentrations of Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn were measured in several soft-tissue types of the Antarctic soft-shelled clam, Laternula elliptica, which had been collected from Rothera Research Station, Adelaide Island, Antarctic Peninsula. Concentrations of Mn, Ni, Cr and Pb were significantly higher in the kidney than in any other soft tissue and highest concentrations of Cu were observed in the digestive gland. In general, the total tissue concentrations of heavy metals in L. elliptica were considered to be at baseline levels, except for Cu in organisms near the end of the runway. Copper concentrations were an order of magnitude greater (357 g/g dry weight) than baseline levels, suggesting anthropogenic contamination or an unidentified natural source. However, there was no indication of anthropogenic metal contamination occurring close to the sewage outfall at Rothera, which is a significant metal source. The results indicate that L. elliptica is a useful long-term biomonitor of heavy metal contamination in Antarctic coastal waters.last_img read more

Human exposure to ultraviolet radiation at the Antipodes – a comparison between an Antarctic (67oS) and Arctic (75oN) location

first_imgWe used ultraviolet radiation dosimeters to investigate human exposure at two polar latitudes with a 24-h photoperiod: at Rothera Station (UK) (67degreesS) and at a field camp in the Haughton impact structure in the Canadian High Arctic (75degreesN). Mean personal UV radiation exposure in the Antarctic location was 4.3 times greater than that in the Arctic location, even in the abence of ozone depletion. More than zenith angle accounted for the higher UV exposure. Widespread snow and ice covers, and probably less atmospheric pollution, caused higher personal exposures. Although the mean exposures were higher in the Antarctic location, the mean exposure ratio in the Antarctic (0.20 +/- 0.09) was similar to the value measured in the Arctic (0.27 +/- 0.09) on clear days. We use the Antarctic ratio to provide quantitative estimates of UV-radiation exposure for workers at the Geographical South Pole for the winter solstice under a constant 24-h photoperiod. Exposure ratios can be used to translate measurements of UV radiation by horizontally fixed spectroradiometers into estimates of the mean exposures expected in populations at polar latitudes, although variations between individuals are large. The data have implications for determining the UV exposures of indigenous high-latitude populations.last_img read more

Transport of antarctic krill (Euphausia superba) across the Scotia Sea. Part II: Krill growth and survival

first_imgA time-dependent, size-structured, physiologically based krill growth model was used in conjunction with a circulation model to test the hypothesis that Antarctic krill (Euphausia superba) populations at South Georgia are sustained by import of individuals from upstream regions. Surface phytoplankton concentrations along the simulated drifter trajectories were extracted from historical Coastal Zone Color Scanner (CZCS) measurements and sea ice biota concentrations were calculated from sea ice concentration and extent extracted along drifter trajectories from Special Sensor Microwave/Imager measurements. As additional food sources, a time series of heterotrophic food was constructed from historical data, and time series of detritus concentrations were calculated using phytoplankton concentrations extracted from CZCS measurements together with measured particulate organic carbon to chlorophyll a ratios. These food resources along specified drifter trajectories were then input to the krill growth model to determine the size and viability of krill during transport from the source region to South Georgia. The krill growth model simulations showed that no single food source can support continuous growth of krill during the 58–306 days needed for transport to South Georgia. However, under the current assumptions results indicate that combinations of food sources during the transport time enhanced krill survival, with heterotrophic food and detritus being particularly important during periods of low phytoplankton concentrations. The growth model simulations also showed that larval and juvenile krill originating along the western Antarctic Peninsula can grow to 1+ (14–36 mm) and 2+ (26–45 mm) age and size classes observed at South Georgia during the time needed for transport to this region. Krill originating in the Weddell Sea need 20 months for transport, which allows retention in a potentially high food environment, provided by sea ice, for almost 1 year. Krill then complete transport to South Georgia in the following year and larval and juvenile krill grow to 2+ (26–45 mm) and 3+ (35–60 mm) age and size classes during transport. The results of this study show that the successful transport of krill to South Georgia depends on a multitude of factors, such as the location of the spawning area and timing of spawning, food concentrations during transport, predation, and variations in the location of the Southern Antarctic Circumpolar Current Front (SACCF) and in sea ice extent.last_img read more

The Greenland Ice Core Chronology 2005, 15–42 ka. Part 2: comparison to other records

first_imgA new Greenland Ice Core Chronology (GICC05) based on multi-parameter counting of annual layers has been obtained for the last 42 ka. Here we compare the glacial part of the new time scale, which is based entirely on records from the NorthGRIP ice core, to existing time scales and reference horizons covering the same period. These include the GRIP and NorthGRIP modelled time scales, the Meese-Sowers GISP2 counted time scale, the Shackleton–Fairbanks GRIP time scale (SFCP04) based on 14C calibration of a marine core, the Hulu Cave record, three volcanic reference horizons, and the Laschamp geomagnetic excursion event occurring around Greenland Interstadial 10. GICC05 is generally in good long-term agreement with the existing Greenland ice core chronologies and with the Hulu Cave record, but on shorter time scales there are significant discrepancies. Around the Last Glacial Maximum there is a more than 1 ka age difference between GICC05 and SFCP04 and a more than 0.5 ka discrepancy in the same direction between GICC05 and the age of a recently identified tephra layer in the NorthGRIP ice core. Both SFCP04 and the tephra age are based on 14C-dated marine cores and fixed marine reservoir ages. For the Laschamp event, GICC05 agrees with a recent independent dating within the uncertainties.last_img read more

Assessing the regional disparities in geoengineering impacts

first_imgSolar Radiation Management (SRM) Geoengineering may ameliorate many consequences of global warming but also has the potential to drive regional climates outside the envelope of greenhouse-gas induced warming, creating ‘novel’ conditions, and could affect precipitation in some regions disproportionably. Here, using a fully coupled climate model we explore some new methodologies for assessing regional disparities in geoengineering impacts. Taking a 4 x CO2 climate and an idealized ‘sunshade’ SRM strategy, we consider different fractions of the maximum theoretical, 4 x CO2-cancelling global mean cooling. Whilst regional predictions in particularly relatively low resolution global climate models must be treated with caution, our simulations indicate that it might be possible to identify a level of SRM geoengineering capable of meeting multiple targets, such as maintaining a stable mass balance of the Greenland ice sheet and cooling global climate, but without reducing global precipitation below pre-industrial or exposing significant fractions of the Earth to ‘novel’ climate conditions. Citation: Irvine, P. J., A. Ridgwell, and D. J. Lunt (2010), Assessing the regional disparities in geoengineering impacts, Geophys. Res. Lett., 37, L18702, doi:10.1029/2010GL044447.last_img read more

Sensitivity of Pliocene ice sheets to orbital forcing

first_imgThe stability of the Earth’s major ice sheets is a critical uncertainty in predictions of future climate and sea level change. One method of investigating the behaviour of the Greenland and the Antarctic ice sheets in a warmer-than-modern climate is to look back at past warm periods of Earth history, for example the Pliocene. This paper presents climate and ice sheet modelling results for the mid-Pliocene warm period (mPWP; 3.3 to 3.0 million years ago), which has been identified as a key interval for understanding warmer-than-modern climates (Jansen et al., 2007). Using boundary conditions supplied by the United States Geological Survey PRISM Group (Pliocene Research, Interpretation and Synoptic Mapping), the Hadley Centre coupled ocean–atmosphere climate model (HadCM3) and the British Antarctic Survey Ice Sheet Model (BASISM), we show large reductions in the Greenland and East Antarctic Ice Sheets (GrIS and EAIS) compared to modern in standard mPWP experiments. We also present the first results illustrating the variability of the ice sheets due to realistic orbital forcing during the mid-Pliocene. While GrIS volumes are lower than modern under even the most extreme (cold) mid-Pliocene orbit (losing at least 35% of its ice mass), the EAIS can both grow and shrink, losing up to 20% or gaining up to 10% of its present-day volume. The changes in ice sheet volume incurred by altering orbital forcing alone means that global sea level can vary by more than 25 m during the mid-Pliocene. However, we have also shown that the response of the ice sheets to mPWP orbital hemispheric forcing can be in anti-phase, whereby the greatest reductions in EAIS volume are concurrent with the smallest reductions of the GrIS. If this anti-phase relationship is in operation throughout the mPWP, then the total eustatic sea level response would be dampened compared to the ice sheet fluctuations that are theoretically possible. This suggests that maximum eustatic sea level rise does not correspond to orbital maxima, but occurs at times where the anti-phasing of Northern and Southern Hemisphere ice sheet retreat is minimised.last_img read more

Modeling the influence of the Weddell Polynya on the Filchner-Ronne Ice Shelf cavity

first_imgOpen-ocean polynyas in the Weddell Sea of Antarctica are the product of deep convection, which transports Warm Deep Water (WDW) to the surface and melts sea ice or prevents its formation. These polynyas occur only rarely in the observational record, but are a near-permanent feature of many climate and ocean simulations. A question not previously considered is the degree to which the Weddell Polynya affects the nearby Filchner-Ronne Ice Shelf (FRIS) cavity. Here we assess these effects using regional ocean model simulations of the Weddell Sea and FRIS, where deep convection is imposed with varying area, location, and duration. In these simulations, the idealised Weddell Polynyas consistently cause an increase in WDW transport onto the continental shelf, as a result of density changes above the shelf break. This leads to saltier, denser source waters for the FRIS cavity, which then experiences stronger circulation and increased ice shelf basal melting. It takes approximately 14 years for melt rates to return to normal after the deep convection ceases. Weddell Polynyas similar to those seen in observations have a modest impact on FRIS melt rates, which is within the range of simulated interannual variability. However, polynyas which are larger or closer to the shelf break, such as those seen in many ocean models, trigger a stronger response. These results suggest that ocean models with excessive Weddell Sea convection may not be suitable boundary conditions for regional models of the Antarctic continental shelf and ice shelf cavities.last_img read more

Thousands of fans celebrate the Washington Capitals’ first Stanley Cup win

first_img Written by June 12, 2018 /Sports News – National Thousands of fans celebrate the Washington Capitals’ first Stanley Cup win FacebookTwitterLinkedInEmailYasin Ozturk/Anadolu Agency/Getty Images(WASHINGTON) — A sea of red filled Constitution Avenue in Washington, D.C., on Tuesday as fans celebrated the Washington Capitals first Stanley Cup win.Dressed head to toe in red, fans lined the victory parade route that ran down Constitution Avenue and concluded with a rally at the National Mall.“You think it’s going to be crazy but it’s actually nuts,” Capitals hockey player Alex Ovechkin said at the rally. “You guys are killing it.”A number of buses carried the team and their family members, the last bus hosted Ovechkin who held the trophy in the air as fans cheered.“This happens because they support as much as you are,” Ovechkin said at the rally. “We want to say to our families and you guys, ‘thank you very much.’”Thousands of fans attended the event and one Twitter user joked that people in Washington, D.C., likely avoided going to work to attend the celebratory occasion.At the rally, right winger T.J. Oshie teased that the Washington Capitals would win back-to-back championships, which garnered a roar of applause from the crowd.Before the end of the event, the team and crowd sang, “We are the Champions” and chanted, “Let’s go Caps!”Copyright © 2018, ABC Radio. All rights reserved.center_img Beau Lundlast_img read more

Scoreboard roundup — 10/22/18

first_img Written by October 23, 2018 /Sports News – National Scoreboard roundup — 10/22/18 FacebookTwitterLinkedInEmailiStock/Thinkstock(NEW YORK) — Here are the scores from Saturday’s sports events:NATIONAL BASKETBALL ASSOCIATIONOrlando 93, Boston 90Toronto 127, Charlotte 106Minnesota 101, Indiana 91Milwaukee 124, N-Y Knicks 113Dallas 115, Chicago 109Memphis 92, Utah 84OT Washington 125, Portland 124OT San Antonio 143, L.A. Lakers 142Golden State 123, Phoenix 103NATIONAL HOCKEY LEAGUEColorado 4, Philadelphia 1Carolina 3, Detroit 1OT Winnipeg 5, St. Louis 4Washington 5, Vancouver 2NATIONAL FOOTBALL LEAGUEAtlanta 23, N-Y Giants 20Copyright © 2018, ABC Radio. All rights reserved.center_img Beau Lundlast_img read more