Bryum Hedw. Collected from Lake Vanda, Antarctica

first_imgBryum cf. algens Card, was collected by SCUBA divers from 9-31 m in the benthos of perennially ice-covered Lake Vanda (77°32′S, 161°35′E), Wright Valley, southern Victoria Land, Antarctica. It occurred as a component of a microbial mat consisting primarily of Phormidium frigidum Fritsch, Lyngbya martensiana Menegh. and pennate diatoms. Contrastingly, B. cf. algens was not found in Lakes Bonney, Hoare, Chad and Fryxell located in adjacent Taylor Valley, nor was it found in any ice-free littoral regions of the lakes of Taylor and Wright Valleys investigated during the 1980-81 austral summer. Bryum algens is the most widespread bryophyte south of 56°S in Antarctica. Its wide range of morphological forms has caused many problems in its taxonomy. Based upon examinations by one of us (R. I. L. S.), it is probable that B. korotkevicziae Sav.-Lyub. & Z. Smirn. and its variety hollebachii Sav.-Lyub. & Z. Smirn. and an unidentified aquatic Bryum sp. from Ablation Valley, Antarctica may be ecotypes of B. algens. The findings of B. cf. algens in Lake Vanda is the southernmost known occurrence of a moss from a perennially liquid deep water (>0.5 m) habitat.last_img read more

Seasonal variation in the cold hardiness of three species of free-living Antarctic nematodes

first_imgThe physiological adaptations required to survive exposure to low temperatures must be of great importance in allowing nematodes to colonize extreme terrestrial environments, such as Antarctic fellfields. Seasonal variation in the cold hardiness of three species of free-living nematodes was studied by monitoring supercooling points from approximately monthly samples over a period of 2 years. Two species, Teratocephalus tilbrooki Maslen and Plectus antarcticus de Man coexist within the relatively sheltered cushions and carpets of a moss, whilst the third species, Ditylenchus sp.B, is found in the more exposed aerial thalli of a lichen. Ditylenchus sp.B shows consistent supercooling ability, low enough (c -28⚬C) to avoid any significant incidence of freezing during the study period. Both of the moss-dwelling species, which exhibit bimodal supercooling point distributions with a high group at c -7⚬C and a low group at c -22⚬C encounter field temperatures likely to result in freezing. Only T. tilbrooki exhibits any degree of freeze tolerance. P. antarcticus is unique amongst these three species in showing a marked pattern of seasonal change in cold hardiness. Juvenile nematodes show greater supercooling ability than adults. Increased body pigmentation, possibly related to recent feeding activity, increases the likelihood of P. antarcticus freezing at high temperatures (> -10⚬C), but has no effect on the supercooling ability of Ditylenchus sp.B. Ditylenchus sp.B appears to be capable of preventing the accumulation of any nucleating agents which would cause freezing at high temperatures.last_img read more

Risk estimation of collapse of the West Antarctic ice sheet

first_imgComplete collapse of the West Antarctic Ice Sheet (WAIS) would raise global sea level by around 5 m, but whether collapse is likely, or even possible, has been `glaciology’s grand unsolved problem’ for more than two decades. Collapse of WAIS may result from readjustments continuing since the last glacial maximum, or more recent climate change, but it is also possible that collapse will result from internal flow instabilities, or not occur at all in the present inter-glacial. Such complexity led the Intergovernmental Panel on Climate Change to conclude in its Second Assessment Report that `estimating the likelihood of a collapse during the next century is not yet possible’. However, a refusal by scientists to estimate the risk leaves policy-makers with no sound scientific basis on which to respond to legitimate public concerns. Here we present a discussion of the likelihood of WAIS-collapse, drawing input from an interdisciplinary panel of experts. The results help to summarise the state of scientific knowledge and uncertainty. While the overall opinion of the panel was that WAIS most likely will not collapse in the next few centuries, their uncertainty retains a 5% probability of WAIS causing sea level rise at least 10 mm/year within 200 years. Since this uncertainty reflects both the unpredictability of the physical system and the scientific uncertainty, it will undoubtedly change as a better understanding is established.last_img

Setting a precautionary catch limit for Antarctic krill

first_imgA revised precautionary catch limit for Antarctic krill (Euphausia superba) in the Scotia Sea of 4 million tons wasrecently adopted by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). The limitwas based on a total biomass of 44.3 million tons, as estimated from an acoustic and net survey of krill across the Scotia Sea sector of the Southern Ocean, and a harvest rate of 9.1%, as determined from an analysis of the risks of exceeding defined conservation criteria. We caution, however, that before the fishery can expand to the 4-million-ton level it will be necessary to establish mechanisms to avoid concentration of fishing effort, particularly in proximity to colonies ofland-breeding krill predators, and to consider the effects of krill immigrating into the region from multiple sources.last_img read more

Growth rate and its variability in erect Antarctic bryozoans

first_imgClimate is altering rapidly in parts of the Arctic and Antarctic but we know little about how marine organisms are responding to, or might respond to such changes. Knowledge of within-taxon variability is the vital context (currently missing) to interpretation of environmental signals. We investigated growth in six species and three genera of erect Antarctic bryozoans, an ideal model taxon to investigate such response. Cellarinella margueritae, C. nodulata, C. rogickae, C. watersi, Melicerita obliqua and Stomhypselosaria watersi, extended 3.4, 5.2, 4.6, 4.1, 4.9 and 4.5 mm year−1 and synthesised 24, 55, 45, 176, 34 and 46 mg CaCO3 year−1, respectively. The maximum ages of these species ranged from 11 to 15 years except M. obliqua, which reached 32 years. This is the first investigation of growth rates of closely related Antarctic invertebrate species and reports the slowest growth rates of bryozoans known from anywhere to date. Our data coupled with that from literature shows that Antarctic bryozoan growth varies <<101 between species, 101 between genera, 102 between morphologies and is ∼101 slower than in tropical or temperate regions. However, within encrusting types the slowest growing species grow at similar rates from poles to tropics. Age was a strong confounding factor across our Antarctic study species but age-standardised data showed a possible decline in annual growth from 1992 to 2003. We identify several factors increasing this environmental signal strength, including (1) the importance of generic (though not necessarily species) identification and (2) use of dry-mass or ash-free dry-mass as the measures of growth.last_img read more

Long-range dependence and climate noise characteristics of Antarctic temperature data

first_imgThis study examines the long-range dependency, climate noise characteristics, and nonlinear temperature trends of eight Antarctic stations from the Reference Antarctic Data for Environmental Research (READER) dataset. Evidence is shown that Antarctic temperatures are long-range dependent. To identify possible nonlinear trends, the ensemble empirical mode decomposition (EEMD) method is used, and then the question of whether the observed trends can arise from internal atmospheric fluctuations is examined. To answer this question, surrogate data are generated from two paradigmatic null models: a standard first-order autoregressive process representing a short-range dependent process and a fractional integrated process representing a long-range dependent process. It is found that three of the eight stations show statistically significant trends when tested against the short-range dependent process while only the Faraday-Vernadsky station temperature time series shows a significant trend when tested against the long-range dependent null model. All other considered stations show no trends that are statistically significant against the two null models, and thus they can be explained by internal atmospheric variability. These results imply that more attention should be given to assessing the correlation structure of climate time series.last_img read more

A ‘continuity-index’ for assessing ice-sheet dynamics from radar-sounded internal layers

first_imgRadio-echo sounding (RES) of polar ice sheets reveals extensive internal layering. The degree of continuity of internal layering holds critical information about the ice-flow field, but previous analyses of this parameter have been limited to qualitative classifications. Here we present a new quantitative method for analyzing internal layer continuity—named the continuity-index. When applied to data from Pine Island Glacier, West Antarctica, the new method clearly identifies a continuum of discontinuity of internal layers that corresponds with the current ice-velocity field. The analysis provides further support that the main trunk and tributaries are unlikely to have undergone substantial migration since the deposition of the internal layering. Significantly, our new method for analyzing internal layers is readily transferable across RES datasets, offering promise for data-led assessments of past and present flow dynamics across large areas of Antarctica and Greenland.last_img read more

Spatial patterns in the vertical structure of euphausiids in Gullmarsfjord, Sweden: Identifying influences on bilayer formation and distribution

first_imgThe formation of two vertically discrete layers (bilayers) at night-time is a commonly observed phenomenon in zooplankton and is regularly found in Gullmarsfjord, a fjord with a 50 m sill depth, deep basin and a three-layered water column. In an acoustic and net sampling survey in September 2003, night-time euphausiid layers occurred at 15 and 45 m, with the deeper layer containing relatively higher concentrations of adult Northern krill (Meganyctiphanes norvegica). The main night-time predatory threat came from the upward migration of demersal fish, which reached the deeper but not the shallower euphausiid layer. Shoreward advection of coastal waters across the sill creates a layer of resuspended organic matter between 40 and 50 m. The deeper bilayer was located at those depths, particularly at the mouth of the fjord where this organic matter was most concentrated. Krill in the lower bilayer experienced waters that were 4°C cooler than in the upper bilayer, which can decrease the cost of respiration by around 20%. Accompanying studies have shown significantly higher growth rates in krill consuming sedimentary organic material and benthic filamentous algae. Combined, it appears that energetic benefit and predatory threat were greatest in the deeper rather than the shallower bilayer in Gullmarsfjord. This is the reverse of most other euphausiid habitats, where the highest risk and reward is in the upper bilayer, illustrating that euphausiids adapt their stereotypic vertical migration pattern to local environmental conditions.last_img read more

The growth response of two diatom species to atmospheric dust from the Last Glacial Maximum

first_imgRelief of iron (Fe) limitation in the surface Southern Ocean has been suggested as one driver of the regular glacial-interglacial cycles in atmospheric carbon dioxide (CO2). The proposed cause is enhanced deposition of Fe-bearing atmospheric dust to the oceans during glacial intervals, with consequent effects on export production and the carbon cycle. However, understanding the role of enhanced atmospheric Fe supply in biogeochemical cycles is limited by knowledge of the fluxes and ‘bioavailability’ of atmospheric Fe during glacial intervals. Here, we assess the effect of Fe fertilization by dust, dry-extracted from the Last Glacial Maximum portion of the EPICA Dome C Antarctic ice core, on the Antarctic diatom species Eucampia antarctica and Proboscia inermis. Both species showed strong but differing reactions to dust addition. E. antarctica increased cell number (3880 vs. 786 cells mL-1), chlorophyll a (51 vs. 3.9 μg mL-1) and particulate organic carbon (POC; 1.68 vs. 0.28 μg mL-1) production in response to dust compared to controls. P. inermis did not increase cell number in response to dust, but chlorophyll a and POC per cell both strongly increased compared to controls (39 vs. 15 and 2.13 vs. 0.95 ng cell-1 respectively). The net result of both responses was a greater production of POC and chlorophyll a, as well as decreased Si:C and Si:N incorporation ratios within cells. However, E, antarctica decreased silicate uptake for the same nitrate and carbon uptake, while P. inermis increased carbon and nitrate uptake for the same silicate uptake. This suggests that nutrient utilization changes in response to Fe addition could be driven by different underlying mechanisms between different diatom species. Enhanced supply of atmospheric dust to the surface ocean during glacial intervals could therefore have driven nutrient-utilization changes which could permit greater carbon fixation for lower silica utilization. Additionally, both species responded more strongly to lower amounts of direct Fe chloride addition than they did to dust, suggesting that not all the Fe released from dust was in a bioavailable form available for uptake by diatoms.last_img read more

Cleveland Indians reliever Andrew Miller to miss time with knee ailment

first_imgMay 26, 2018 /Sports News – National Cleveland Indians reliever Andrew Miller to miss time with knee ailment FacebookTwitterLinkedInEmailAllen Kee/ESPN Images(CLEVELAND) — The Cleveland Indians placed star relief pitcher Andrew Miller on the disabled list due to a right knee injury.Miller, who had just recovered from a hamstring injury in his right knee, allowed three runs in the team’s 11-2 loss to the Houston Astros on Friday night.After the game, he told reporters, “I’m definitely not sharp. I wish I had the answers. I think there’s flashes of it, but it’s been a pretty big grind lately.”The Indians call the injury right knee inflammation. Last season, he was placed on the disabled list twice with patellar tendinitis in his right knee.Copyright © 2018, ABC Radio. All rights reserved. Written bycenter_img Beau Lundlast_img read more