Tracing particle paths in the Antarctic ice sheet

first_imgA layer of moraine within the Antarctic ice sheet has been detected in the course of airborne radar ice soundings. The moraine was injected at the margin of the ice and can serve as a tracer to pick out a particle path within the ice. When combined with surface measurements, the ability to trace particle paths should allow detailed modelling of the dynamic behaviour in limited areas.last_img

Quantifying assemblage distinctness with time: an example using temperate epibenthos

first_imgArtificial substrata are an often-used tool in assessing community development; here we quantify the changing presence of functional groups of benthos with replicate, depth, site, and time in order to explain differences in the structure of the surrounding mature communities. We placed replicate, machined slate panels (15 x 15 x 1 cm) in the intertidal, 6 and 12 m at two sites of differing flow rates at Lough Hyne, SW Ireland. They were placed at the same time of year and removed after 2, 6, 12, and 24 months from 1999 to 2001, to compare with a similar experiment run from 1997 to 1999. Furthermore, to examine trends of local assemblages older than 24 months, we examined boulders from each depth/site combination. Percentage cover of 13 functional groups, selected in relation to their competitive abilities, was measured using point intercept analysis of high-resolution digital images of the panels. These data were then quantified using our derived measure of distinctness. Replicates became more similar, and sites and depths both became more distinct with time from 2 to 24 months, although there was less distinctness at the high flow site throughout all stages of the study. Principal components analysis (PCA) of data suggested that all site/depth panel combinations only became truly distinct at the 24-month stage of the study. From 2 to 24 months, ‘good’ competitors increased in space, ‘intermediate’ competitors peaked after approximate to 12 months, and ‘poor’ competitors reduced in their space occupation with increasing time. Both in similarity and space occupation of functional groups, the 1997-1999 and 1999-2001 data showed high levels of pattern convergence. That there was little difference between assemblages at 12 and 24 months validated our upper time limit of period of study, but at 24 months, assemblages still differed from natural substrata and we suggest that many years would have been necessary to eliminate this difference.last_img read more

Atmospheric pressure chemical ionisation liquid chromatography/multistage mass spectrometry for assignment of sedimentary bacteriochlorophyll derivatives

first_imgAtmospheric pressure chemical ionisation liquid chromatography/multistage mass spectrometry (APCI-LC/MSn) provides a rapid, on-line method for the assignment of individual bacteriophaeophorbide c and d methyl esters (BPMEs) in complex mixtures. The MS2 spectrum for each component is diagnostic of the type of BPME (c or d), and characteristic losses in MS5 and MS6 permit assignment of the alkyl substituents at positions C-8 and C-12 of the macrocycle. MS5 mass chromatograms permit the deconvolution of coeluting isobaric BPMEs, revealing the true profiles of the individual components. The distributions are different in lake sediments from la Salada de Chiprana (Spain) and Kirisjes Pond (Antarctica), and a novel BPME c with a neo-pentyl substituent has been observed in the Kirisjes Pond sediment.last_img read more

First bipolar benthic brooder

first_imgA bipolar distribution is one in which a taxon occurs at high northern and southern latitudes but is absent in the latitudes between. In spite of the large distance between the Arctic and Antarctic, there are records of biota with bipolar distributions, both currently and in the geological past. To date, combined morphological and genetic studies of organisms such as bacteria and foram-inifera have confirmed the occurrence of some species in both polar regions. Bipolar genera and families are also known in larger invertebrates, e.g. in crustaceans and molluscs, and a recent Census of Marine Life report suggested that more than 200 metazoan species may have bipolar distributions. Here we investigated specimens of the the cheilostome bryozoan Callpora weslawski from both Arctic and Antarctic localities. To our knowledge this is the first benthic brooder to be found in both polar regions and is the first record of a species of Callopora in Antarctic waters. We used scanning electron microscopy and statistical analyses to confirm the morphological identity of individuals. The encrusting nature of the species, its distribution in the deep Weddell Sea and its rarity mean that genetic confirmation of bipolarity may take years or decades. Possible paths of distribution are discussed, including the Pangea break-up, Plio-Pleistocene glaciations, isothermal submergence via off-shelf or abyssal currents and anthropogenic transport.last_img read more

An observationally validated theory of viscous flow dynamics at the ice-shelf calving front

first_imgAn analytical theory is developed for ice flow velocity in a boundary layer couplet atthe calving front. The theory has simple quantitative characteristics that relate ice front velocity tothickness, strain rate and shelf width, matching one set of empirically derived relationships (Alley andothers, 2008) and implying that these relationships predict ice velocity rather than calving rate. Thetwo boundary layers are where longitudinal and transverse flow fields change from the interior flow topatterns consistent with the calving-front stress condition. Numerical simulations confirm the analyticaltheory. The quantitative predictions of the theory have low sensitivity to unmeasured parameters and to shelf plan aspect ratio, while its robustness arises from its dependence on the scale invariance of the governing equations. The theory provides insights into calving, the stability of ice-shelf calving fronts, the stability of the grounding line of laterally resisted ice streams, and also suggests that the calving front is an instructive dynamical analogue to the grounding line.last_img read more

Late Holocene changes in cyanobacterial community structure in maritime Antarctic lakes

first_imgDespite the dominance of cyanobacteria in polar freshwater aquatic ecosystems, little is known about their past biodiversity and response to climate and environmental changes. We explored the use of light microscopy of microfossils, high performance liquid chromatography of the fossil pigment composition and denaturing gradient gel electrophoresis of fossil 16S rRNA genes to study past and present-day differences in cyanobacterial community structure in response to climate changes in two adjacent maritime Antarctic lakes with contrasting depths (4 and 26 m) and light climates. Light microscopy was of limited use because of degradation of cell structures. Fossil cyanobacterial pigment concentrations were below the detection limits of our method in several sediment samples in the deep lake, but abundant and diverse in the sediment core from the shallow pond, probably as a consequence of increased light availability and/or a more diverse and abundant benthic cyanobacterial flora. Total carotenoid and chlorophyll concentrations were highest in both lakes between ca. 2,950 and 1,800 cal yr BP, which coincides with the late Holocene climate optimum recognised elsewhere in maritime Antarctica. Cyanobacterial molecular diversity was higher in the top few centimeters of the sediments in both lakes. In deeper sediments, the taxonomic turnover of cyanobacteria appeared to be relatively small in response to past climate anomalies in both lakes, underscoring the broad tolerance of cyanobacteria to environmental variability. This, however, may in part be explained by the low taxonomic resolution obtained with the relatively conserved 16S rRNA gene and/or the preferential preservation of particular taxa. Our results highlight the potential of fossil DNA in lake sediments to study colonization and succession dynamics of lacustrine cyanobacteria and warrant further investigation of the factors that affect preservation of cyanobacterial DNA.last_img read more

Dynamic response of Antarctic Peninsula Ice Sheet to potential collapse of Larsen C and George VI ice shelves

first_imgIce shelf break-up and disintegration events over the past 5 decades have led to speed-up, thinning, and retreat of upstream tributary glaciers and increases to rates of global sea-level rise. The southward progression of these episodes indicates a climatic cause and in turn suggests that the larger Larsen C and George VI ice shelves may undergo a similar collapse in the future. However, the extent to which removal of the Larsen C and George VI ice shelves will affect upstream tributary glaciers and add to global sea levels is unknown. Here we apply numerical ice-sheet models of varying complexity to show that the centennial sea-level commitment of Larsen C embayment glaciers following immediate shelf collapse is low ( < 2.5 mm to 2100,  < 4.2 mm to 2300). Despite its large size, Larsen C does not provide strong buttressing forces to upstream basins and its collapse does not result in large additional discharge from its tributary glaciers in any of our model scenarios. In contrast, the response of inland glaciers to a collapse of the George VI Ice Shelf may add up to 8mm to global sea levels by 2100 and 22mm by 2300 due in part to the mechanism of marine ice sheet instability. Our results demonstrate the varying and relative importance to sea level of the large Antarctic Peninsula ice shelves considered to present a risk of collapse.last_img read more

RAD sequencing and a hybrid Antarctic fur seal genome assembly reveal rapidly decaying linkage disequilibrium, global population structure and evidence for inbreeding

first_imgRecent advances in high throughput sequencing have transformed the study of wild organisms by facilitating the generation of high quality genome assemblies and dense genetic marker datasets. These resources have the potential to significantly advance our understanding of diverse phenomena at the level of species, populations and individuals, ranging from patterns of synteny through rates of linkage disequilibrium (LD) decay and population structure to individual inbreeding. Consequently, we used PacBio sequencing to refine an existing Antarctic fur seal (Arctocephalus gazella) genome assembly and genotyped 83 individuals from six populations using restriction site associated DNA (RAD) sequencing. The resulting hybrid genome comprised 6,169 scaffolds with an N50 of 6.21 Mb and provided clear evidence for the conservation of large chromosomal segments between the fur seal and dog (Canis lupus familiaris). Focusing on the most extensively sampled population of South Georgia, we found that LD decayed rapidly, reaching the background level by around 400 kb, consistent with other vertebrates but at odds with the notion that fur seals experienced a strong historical bottleneck. We also found evidence for population structuring, with four main Antarctic island groups being resolved. Finally, appreciable variance in individual inbreeding could be detected, reflecting the strong polygyny and site fidelity of the species. Overall, our study contributes important resources for future genomic studies of fur seals and other pinnipeds while also providing a clear example of how high throughput sequencing can generate diverse biological insights at multiple levels of organization.last_img read more

Discovery of microcystin-producing Anagnostidinema pseudacutissimum from cryopreserved Antarctic cyanobacterial mats

first_imgMicrocystins (MCs) are secondary metabolites produced by cyanobacteria and have been well-documented in temperate and tropical regions. However, knowledge of the production of MCs in extremely cold environments is still in its infancy. Recently, examination of 100-year-old Antarctic cyanobacterial mats collected from Ross Island and the McMurdo Ice Shelf during Captain R.F. Scott’s Discovery Expedition revealed that the presence of MCs in Antarctica is not a new phenomenon. Here, morphological and molecular phylogenetic analyses are used to identify a new microcystin-producing freshwater cyanobacterium, Anagnostidinema pseudacutissimum. The strain was isolated from a deep-frozen (−15 °C) sample collected from a red-brown cyanobacterial mat in a frozen pond at Cape Crozier (Ross Island, continental Antarctica) in 1984–1985. Amplification of the mcyE gene fragment involved in microcystin biosynthesis from A. pseudacutissimum confirmed that it is identical to the sequence from other known microcystin-producing cyanobacteria. Analysis of extracts from this A. pseudacutissimum strain by HPLC-MS/MS confirmed the presence of MC-LR and -YR at concentrations of 0.60 μg/L and MC-RR at concentrations of 0.20 μg/L. This is the first report of microcystin production from a species of Anagnostidinema from Antarctica.last_img read more

Rusnak, Rimando help Real Salt Lake beat Red Bulls 1-0

first_imgMarch 18, 2018 /Sports News – Local Rusnak, Rimando help Real Salt Lake beat Red Bulls 1-0 Robert Lovell FacebookTwitterLinkedInEmailSANDY, Utah (AP) — Albert Rusnak scored on a penalty kick in the opening minutes and Nick Rimando had his MLS-leading 138th career shutout to help Real Salt Lake beat the New York Red Bulls 1-0 on Saturday night in the snow.David Horst drew a foul, conceded by Carlos Rivas, just inside the penalty area and Rusnak converted from the spot to give Real Salt Lake (1-1-1) the lead in the fourth minute.Rimando, a five-time MLS All-Star, finished with four saves, including a pair of spectacular diving stops. The 38-year old made a diving one-handed stop of a half-volley by Vincent Bezecourt in the 26th and another diving save in the 54th minute, turning away Bezecourt’s header from just outside the 6-yard box.The Red Bulls (1-1-0) are winless, including two losses, in their last three games against RSL.Chris Wingert, who played 14 MLS seasons and was a starter for Real Salt Lake’s 2009 MLS Cup championship team, was honored at halftime. The defender, who played 10 seasons for RSL, announced his retirement on Feb. 19.center_img Written bylast_img read more