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1
Lyons, W. Berry, Kathleen A. Welch, Christopher B. Gardner, Chris Jaros, Daryl L. Moorhead, Jennifer L. Knoepfle e Peter T. Doran. "The geochemistry of upland ponds, Taylor Valley, Antarctica". Antarctic Science 24, n. 1 (23 settembre 2011): 3–14. http://dx.doi.org/10.1017/s0954102011000617.
Testo completoAbstract (sommario):
AbstractThe McMurdo Dry Valleys of Antarctica are the largest ice-free region on the continent. These valleys contain numerous water bodies that receive seasonal melt from glaciers. For forty years, research emphasis has been placed on the larger water bodies, the permanent ice-covered lakes. We present results from the first study describing the geochemistry of ponds in the higher elevations of Taylor Valley. Unlike the lakes at lower elevations, the landscape on which these ponds lie is among the oldest in Taylor Valley. These upland ponds wax and wane in size depending on the local climatic conditions, and their ionic concentrations and isotopic composition vary annually depending on the amount of meltwater generated and their hydrologic connectivity. This study evaluates the impact of changes in summer climate on the chemistry of these ponds. Although pond chemistry reflects the initial meltwater chemistry, dissolution and chemical weathering within the stream channels, and possibly permafrost fluid input, the primary control is the dilution effect of glacier melt during warmer summers. These processes lead to differences in solute concentrations and ionic ratios between ponds, despite their nearby proximity. The change in size of these ponds over time has important consequences on their geochemical behaviour and potential to provide water and solutes to the subsurface.
2
Griffin, Benjamin M., e James M. Tiedje. "Microbial reductive dehalogenation in Antarctic melt pond sediments". Antarctic Science 19, n. 4 (2 agosto 2007): 411–16. http://dx.doi.org/10.1017/s0954102007000570.
Testo completoAbstract (sommario):
AbstractDue to its geographic isolation and relatively limited human impact, Antarctica is a promising location to study the eco-physiology of natural halogen cycles. Anaerobic sediments from Antarctic melt ponds on Ross Island and on the McMurdo Ice Shelf near Bratina Island were tested for activity of microbial reductive dehalogenation. Anaerobic enrichment cultures were established with potential electron donors and tetrachloroethene, trichloroethene, 2-bromophenol, 2-chlorophenol, 3-bromobenzoate, or 3-chlorobenozoate, as model halocarbon electron acceptors. Dechlorination of aromatic compounds was limited, whereas 2-bromophenol was debrominated in seven of the eight sediments and one site also showed debromination of 3-bromobenzoate. A most probable number estimate with 2-bromophenol at one site revealed 103–104cultivatable debrominators per gram of sediment (wet weight). Chloroethene dechlorination was slow and primarily produced trichloroethene from tetrachloroethene, although bothcis-andtrans-dichloroethene were detected in certain enrichments upon extended incubation. These results demonstrate the presence of reductive dehalogenating activity in anaerobic, Antarctic melt-pond sediments and expand the known metabolic diversity of Antarctic microorganisms.
3
Howard-Williams, Clive, e Ian Hawes. "Ecological processes in Antarctic inland waters: interactions between physical processes and the nitrogen cycle". Antarctic Science 19, n. 2 (22 maggio 2007): 205–17. http://dx.doi.org/10.1017/s0954102007000284.
Testo completoAbstract (sommario):
AbstractIn this review we consider the physical processes that shape inland aquatic ecosystems and how these affect ecosystem processes, with particular focus on the nitrogen cycle. Inland Antarctica is dominated by microbial communities that are usually concentrated in, or adjacent to, habitats with free water. The presence of free vs frozen water is dependent on very small changes in temperature around 0°C, so significant variability in the distribution of free water can be expected in response to variations in climate over diel, decadal, to millennial time scales and a range of spatial scales. Antarctic inland waters take many forms: snow-surface melt pockets, cryoconites, basal regions of wet-based glaciers, ponds (varying in salinity and degree of desiccation), melt streams, perennially and seasonally ice covered lakes and even hypersaline, ice free lakes. The important processes and transformations that characterize the nitrogen cycle worldwide have all been identified in Antarctic inland waters and in some cases (e.g. N-uptake, N-fixation), rates are similar to those at lower latitudes. The unique features of Antarctic ecosystems stem from the extreme and variable physical conditions under which these processes operate rather than any unique ecosystem processes per se.
4
Howard-Williams, Clive. "Climate change as a unifying theme in Antarctic research". Antarctic Science 13, n. 4 (dicembre 2001): 353. http://dx.doi.org/10.1017/s0954102001000499.
Testo completoAbstract (sommario):
How many times have you seen statements similar to the following: “Antarctica is a global barometer”, “Antarctica is a warning beacon for global change”, or “Antarctica is a warning beacon for global change”, or “Antarctica is the most sensitive continent to climate change”? The frequency of such statements in this, and other polar journals, is significant. We know that the polar regions are highly sensitive to natural and human induced changes that originate elsewhere on our planet, and the literature is extensive and growing. At the large scale there is increasing evidence of both direct and indirect linkages between climate patterns (e.g. ENSO) in the Pacific and Atlantic oceans and Antarctic climate. At a smaller scale are the follow-on linkages to glacier dynamics, including surface melt, glacier stream flows, lake levels, beaches, sea-ice dynamics and ice tongues. All of these have major repercussions on Antarctic ecosystems. The phase change from water (liquid) to ice (solid) occurs over avery small temperature range (depending on salinity, pressure etc). Thus, for a pond ecosystem, a change in temperature of less than one degree Celsius means the difference between a functioning aquatic ecosystem, and a frozen ecosystem. The recent IPCC report (Climate Change 2001 [3 vols], Cambridge University Press) leaves little doubt of the significant changes to world climate now taking place. As Antarctic scientists we surely must therefore consider that the principal issue to be addressed in Antarctica at present is that of “Responses to a changing climate”.
5
Kyrö, E. M., V. M. Kerminen, A. Virkkula, M. Dal Maso, J. Parshintsev, J. Ruíz-Jimenez, L. Forsström et al. "Antarctic new particle formation from continental biogenic precursors". Atmospheric Chemistry and Physics Discussions 12, n. 12 (19 dicembre 2012): 32741–94. http://dx.doi.org/10.5194/acpd-12-32741-2012.
Testo completoAbstract (sommario):
Abstract. Over Antarctica, aerosol particles originate almost entirely from marine areas, with minor contribution from long-range transported dust or anthropogenic material. The Antarctic continent itself, unlike all other continental areas, has been thought to be practically free of aerosol sources. Here we present evidence of local aerosol production associated with melt-water ponds in the continental Antarctica. We show that in air masses passing such ponds, new aerosol particles are efficiently formed and these particles grow up to sizes where they may act as cloud condensation nuclei (CCN). The precursor vapours responsible for aerosol formation and growth originate very likely from highly abundant cyanobacteria Nostoc commune (Vaucher) communities of local ponds. This is the first time when freshwater vegetation has been identified as an aerosol precursor source. The influence of the new source on clouds and climate may increase in future Antarctica, and possibly elsewhere undergoing accelerating summer melting of semi-permanent snow cover.
6
Kyrö, E. M., V. M. Kerminen, A. Virkkula, M. Dal Maso, J. Parshintsev, J. Ruíz-Jimenez, L. Forsström et al. "Antarctic new particle formation from continental biogenic precursors". Atmospheric Chemistry and Physics 13, n. 7 (2 aprile 2013): 3527–46. http://dx.doi.org/10.5194/acp-13-3527-2013.
Testo completoAbstract (sommario):
Abstract. Over Antarctica, aerosol particles originate almost entirely from marine areas, with minor contribution from long-range transported dust or anthropogenic material. The Antarctic continent itself, unlike all other continental areas, has been thought to be practically free of aerosol sources. Here we present evidence of local aerosol production associated with melt-water ponds in continental Antarctica. We show that in air masses passing such ponds, new aerosol particles are efficiently formed and these particles grow up to sizes where they may act as cloud condensation nuclei (CCN). The precursor vapours responsible for aerosol formation and growth originate very likely from highly abundant cyanobacteria Nostoc commune (Vaucher) communities of local ponds. This is the first time freshwater vegetation has been identified as an aerosol precursor source. The influence of the new source on clouds and climate may increase in future Antarctica, and possibly elsewhere undergoing accelerating summer melting of semi-permanent snow cover.
7
Gourdal, Margaux, Martine Lizotte, Guillaume Massé, Michel Gosselin, Michel Poulin, Michael Scarratt, Joannie Charette e Maurice Levasseur. "Dimethyl sulfide dynamics in first-year sea ice melt ponds in the Canadian Arctic Archipelago". Biogeosciences 15, n. 10 (29 maggio 2018): 3169–88. http://dx.doi.org/10.5194/bg-15-3169-2018.
Testo completoAbstract (sommario):
Abstract. Melt pond formation is a seasonal pan-Arctic process. During the thawing season, melt ponds may cover up to 90 % of the Arctic first-year sea ice (FYI) and 15 to 25 % of the multi-year sea ice (MYI). These pools of water lying at the surface of the sea ice cover are habitats for microorganisms and represent a potential source of the biogenic gas dimethyl sulfide (DMS) for the atmosphere. Here we report on the concentrations and dynamics of DMS in nine melt ponds sampled in July 2014 in the Canadian Arctic Archipelago. DMS concentrations were under the detection limit (< 0.01 nmol L−1) in freshwater melt ponds and increased linearly with salinity (rs = 0.84, p ≤ 0.05) from ∼ 3 up to ∼ 6 nmol L−1 (avg. 3.7 ± 1.6 nmol L−1) in brackish melt ponds. This relationship suggests that the intrusion of seawater in melt ponds is a key physical mechanism responsible for the presence of DMS. Experiments were conducted with water from three melt ponds incubated for 24 h with and without the addition of two stable isotope-labelled precursors of DMS (dimethylsulfoniopropionate), (D6-DMSP) and dimethylsulfoxide (13C-DMSO). Results show that de novo biological production of DMS can take place within brackish melt ponds through bacterial DMSP uptake and cleavage. Our data suggest that FYI melt ponds could represent a reservoir of DMS available for potential flux to the atmosphere. The importance of this ice-related source of DMS for the Arctic atmosphere is expected to increase as a response to the thinning of sea ice and the areal and temporal expansion of melt ponds on Arctic FYI.
8
Geilfus, N. X., R. J. Galley, O. Crabeck, T. Papakyriakou, J. Landy, J. L. Tison e S. Rysgaard. "Inorganic carbon dynamics of melt pond-covered first year sea ice in the Canadian Arctic". Biogeosciences Discussions 11, n. 5 (23 maggio 2014): 7485–519. http://dx.doi.org/10.5194/bgd-11-7485-2014.
Testo completoAbstract (sommario):
Abstract. Melt pond formation is a common feature of the spring and summer Arctic sea ice. However, the role of the melt ponds formation and the impact of the sea ice melt on both the direction and size of CO2 flux between air and sea is still unknown. Here we describe the CO2-carbonate chemistry of melting sea ice, melt ponds and the underlying seawater associated with measurement of CO2 fluxes across first year landfast sea ice in the Resolute Passage, Nunavut, in June 2012. Early in the melt season, the increase of the ice temperature and the subsequent decrease of the bulk ice salinity promote a strong decrease of the total alkalinity (TA), total dissolved inorganic carbon (TCO2) and partial pressure of CO2 (pCO2) within the bulk sea ice and the brine. Later on, melt pond formation affects both the bulk sea ice and the brine system. As melt ponds are formed from melted snow the in situ melt pond pCO2 is low (36 μatm). The percolation of this low pCO2 melt water into the sea ice matrix dilutes the brine resulting in a strong decrease of the in situ brine pCO2 (to 20 μatm). As melt ponds reach equilibrium with the atmosphere, their in situ pCO2 increase (up to 380 μatm) and the percolation of this high concentration pCO2 melt water increase the in situ brine pCO2 within the sea ice matrix. The low in situ pCO2 observed in brine and melt ponds results in CO2 fluxes of −0.04 to −5.4 mmol m–2 d–1. As melt ponds reach equilibrium with the atmosphere, the uptake becomes less significant. However, since melt ponds are continuously supplied by melt water their in situ pCO2 still remains low, promoting a continuous but moderate uptake of CO2 (~ −1mmol m–2 d–1). The potential uptake of atmospheric CO2 by melting sea ice during the Arctic summer has been estimated from 7 to 16 Tg of C ignoring the role of melt ponds. This additional uptake of CO2 associated to Arctic sea ice needs to be further explored and considered in the estimation of the Arctic Ocean's overall CO2 budget.
9
Mora, S. J. De, R. F. Whitehead e M. Gregory. "The chemical composition of glacial melt water ponds and streams on the McMurdo Ice Shelf, Antarctica". Antarctic Science 6, n. 1 (marzo 1994): 17–27. http://dx.doi.org/10.1017/s0954102094000039.
Testo completoAbstract (sommario):
Melt waters cover c. 20% of the McMurdo Ice Shelf during the austral summer. The streams, ponds, and lakes up to 104 m2 in area occur in two types of terrain systems with differing morphological, chemical, and biological characteristics: pinnacled ice (PI) areas with sparse sediment cover, low relief, and little biomass; and ice-cored moraine (ICM) areas with 10–20 cm sediment cover, hummocky topography with up to 20 m relief, occasional mirabilite deposits, and dense benthic cyanobacterial mats. Pond water composition in the two areas is markedly different. PI area melt waters have low salinities, <2270 mg 1−1 total dissolved salts (TDS), and near neutral pH, mean = 7.8. The chemical composition of PI waters closely follows that of diluted sea water, suggesting that the release of ions from the sea ice matrix of the ice shelf is the major solute source. In contrast, ICM area melt waters have a wide range of salinities, up to 60 400 mg 1−1 TDS and alkaline pH, mean = 9.3. The chemical composition in c. 40% of the ICM ponds investigated did not resemble that of sea water, but had higher relative abundances of SO2−4, Na+, K+ and Ca2+. Leaching of local salt deposits, particularly mirabilite, weathering of surficial sediments, and morphological features promoting closed-basin brine evolution are possible contributing factors to the enrichments.
10
De Mora, S. J., P. A. Lee, A. Grout, C. Schall e K. G. Heumann. "Aspects of the biogeochemistry of sulphur in glacial melt water ponds on the McMurdo Ice Shelf, Antarctica". Antarctic Science 8, n. 1 (marzo 1996): 15–22. http://dx.doi.org/10.1017/s0954102096000041.
Testo completoAbstract (sommario):
The distribution of dimethylsulphide (DMS), together with the precursor dimethylsulphonio-propionate (DMSP) and the oxidation product dimethylsulphoxide (DMSO), was measured in melt waters on the McMurdo Ice Shelf in the immediate vicinity of Bratina Island. Conductivity in these sulphate dominated ponds was extremely variable, ranging from 0.106–52.3 mS cm−1. Similarly, chlorophyll a concentrations in the pond waters (1–150 μg 1−1) and mats (1.4–33 μg cm−2) differed considerably. The biomass was dominated by benthic felts of phototrophic cyanobacteria, which might act as a source of biogenic sulphur compounds in the ponds. The mean (and ranges) of concentrations of dissolved sulphur compounds (nmol 1−1) were: CS2 0.16 (<0.04–1.29); DMSPd 0.6 (<0.07–8.4); DMS 3.5 (<0.07–183); DMSO 27.9 (15.5–184.5). Very high concentrations of DMSO were ubiquitous in the ponds in the ice-cored moraine region of the ice shelf, with dissolved concentrations having been 1–2 orders of magnitude greater than those of DMS or DMSPd. It is difficult to ascribe the formation of DMSO solely to the conventionally accepted pathways of DMS oxidation by either bacterial activity or photochemical reactions. A direct biosynthetic production from phytoplankton or bacteria might be involved which means that DMSO in aquatic environments could act as a significant source of DMS rather than as a sink as generally supposed.
11
Pridmore, R. D., W. N. Vant e V. J. Cummings. "Factors affecting the water clarity of ponds on the McMurdo Ice Shelf, Antarctica". Antarctic Science 7, n. 2 (giugno 1995): 145–48. http://dx.doi.org/10.1017/s0954102095000204.
Testo completoAbstract (sommario):
The clarity of 39 meltwater ponds on the McMurdo Ice Shelf was determined as the horizontal viewing range of a black disc. Visual ranges varied widely from pond to pond from 0.14–5 m; so did the concentrations of optically-active constituents, including the suspended particulates, phytoplankton (10-fold variation) and inorganic suspensoids (> 100-fold), and dissolved yellow substance (10-fold). In six of the ponds the ratio of beam attenuation coefficient to total suspended solids concentration was low (< 0.6 m2 g−1) compared to that in the others (0.7–2.0 m2 g−1, suggesting that generally larger particles were present suspended in the water in these ponds. In both groups, relationships between beam attenuation and constituent concentrations indicated that much of the attenuation was due to inorganic suspensoids. Organic detritus also appeared to be important in many ponds, while phytoplankton and dissolved yellow substance were generally less important. Even though the clarity of many of the ponds was poor, their relative shallowness meant levels of underwater light were probably generally adequate for benthic plant growth.
12
Bates, N. R., R. Garley, K. E. Frey, K. L. Shake e J. T. Mathis. "Sea-ice melt CO<sub>2</sub>–carbonate chemistry in the western Arctic Ocean: meltwater contributions to air–sea CO<sub>2</sub> gas exchange, mixed-layer properties and rates of net community production under sea ice". Biogeosciences 11, n. 23 (8 dicembre 2014): 6769–89. http://dx.doi.org/10.5194/bg-11-6769-2014.
Testo completoAbstract (sommario):
Abstract. The carbon dioxide (CO2)-carbonate chemistry of sea-ice melt and co-located, contemporaneous seawater has rarely been studied in sea-ice-covered oceans. Here, we describe the CO2–carbonate chemistry of sea-ice melt (both above sea-ice as "melt ponds" and below sea-ice as "interface waters") and mixed-layer properties in the western Arctic Ocean in the early summer of 2010 and 2011. At 19 stations, the salinity (∼0.5 to <6.5), dissolved inorganic carbon (DIC; ∼20 to <550 μmol kg−1) and total alkalinity (TA; ∼30 to <500 μmol kg−1) of above-ice melt pond water was low compared to the co-located underlying mixed layer. The partial pressure of CO2 (pCO2) in these melt ponds was highly variable (∼<10 to >1500 μatm) with the majority of melt ponds acting as potentially strong sources of CO2 to the atmosphere. The pH of melt pond waters was also highly variable ranging from mildly acidic (6.1 to 7) to slightly more alkaline than underlying seawater (>8.2 to 10.8). All of the observed melt ponds had very low (<0.1) saturation states (Ω) for calcium carbonate (CaCO3) minerals such as aragonite (Ωaragonite). Our data suggest that sea-ice generated alkaline or acidic type melt pond water. This melt water chemistry dictates whether the ponds are sources of CO2 to the atmosphere or CO2 sinks. Below-ice interface water CO2–carbonate chemistry data also indicated substantial generation of alkalinity, presumably owing to dissolution of CaCO3 in sea-ice. The interface waters generally had lower pCO2 and higher pH/Ωaragonite than the co-located mixed layer beneath. Sea-ice melt thus contributed to the suppression of mixed-layer pCO2, thereby enhancing the surface ocean's capacity to uptake CO2 from the atmosphere. Our observations contribute to growing evidence that sea-ice CO2–carbonate chemistry is highly variable and its contribution to the complex factors that influence the balance of CO2 sinks and sources (and thereby ocean acidification) is difficult to predict in an era of rapid warming and sea-ice loss in the Arctic Ocean.
13
Webster-Brown, J., M. Gall, J. Gibson, S. Wood e I. Hawes. "The biogeochemistry of meltwater habitats in the Darwin Glacier region (80°S), Victoria Land, Antarctica". Antarctic Science 22, n. 6 (dicembre 2010): 646–61. http://dx.doi.org/10.1017/s0954102010000787.
Testo completoAbstract (sommario):
AbstractMeltwater habitats in the Darwin Glacier region, Victoria Land (80°S), were sampled in December 2007 and January 2009 to characterize their microbial and metazoan ecology, nutrient status and geochemistry. Targeted areas included terrestrial ponds of the Grant Valley, Lake Wellman, Tentacle Ridge and Diamond Hill, and supraglacial ponds and cryoconite holes of the lower Darwin Glacier. Geochemistry ranged from Na-Cl dominated terrestrial ponds to Na-HCO3dominated, dilute supraglacial ponds and cryoconites. All showed the nitrate enrichment typical of inland ponds of Victoria Land (up to 13 g.l-1NO3-N), with some precipitating nitratine (NaNO3) salt. Elevated pH indicated ongoing photosynthetic processes. Benthic microbial mats were thin and poorly developed, dominated by oscillatoriacean cyanobacteria. Nitrogen-fixing genera were generally absent and diatoms were rare. A large (20 μm long)Cyanothecespecies was the most abundant cyanobacterium in the water and in sediments of the cryoconites. DNA finger-printing identified distinct differences in cyanobacterial and bacterial community structure between the cryoconites, terrestrial ponds and ponds on glacial margins. Eleven metazoan species were identified, with rotifers being the most abundant. Pond substrate (terrestrial rock, ice-cored moraine or supraglacial ice) proved to be a more significant influence on biogeochemistry than other aspects of geography or climatic conditions.
14
Geilfus, N. X., R. J. Galley, O. Crabeck, T. Papakyriakou, J. Landy, J. L. Tison e S. Rysgaard. "Inorganic carbon dynamics of melt-pond-covered first-year sea ice in the Canadian Arctic". Biogeosciences 12, n. 6 (31 marzo 2015): 2047–61. http://dx.doi.org/10.5194/bg-12-2047-2015.
Testo completoAbstract (sommario):
Abstract. Melt pond formation is a common feature of spring and summer Arctic sea ice, but the role and impact of sea ice melt and pond formation on both the direction and size of CO2 fluxes between air and sea is still unknown. Here we report on the CO2–carbonate chemistry of melting sea ice, melt ponds and the underlying seawater as well as CO2 fluxes at the surface of first-year landfast sea ice in the Resolute Passage, Nunavut, in June 2012. Early in the melt season, the increase in ice temperature and the subsequent decrease in bulk ice salinity promote a strong decrease of the total alkalinity (TA), total dissolved inorganic carbon (TCO2) and partial pressure of CO2 (pCO2) within the bulk sea ice and the brine. As sea ice melt progresses, melt ponds form, mainly from melted snow, leading to a low in situ melt pond pCO2 (36 μatm). The percolation of this low salinity and low pCO2 meltwater into the sea ice matrix decreased the brine salinity, TA and TCO2, and lowered the in situ brine pCO2 (to 20 μatm). This initial low in situ pCO2 observed in brine and melt ponds results in air–ice CO2 fluxes ranging between −0.04 and −5.4 mmol m−2 day−1 (negative sign for fluxes from the atmosphere into the ocean). As melt ponds strive to reach pCO2 equilibrium with the atmosphere, their in situ pCO2 increases (up to 380 μatm) with time and the percolation of this relatively high concentration pCO2 meltwater increases the in situ brine pCO2 within the sea ice matrix as the melt season progresses. As the melt pond pCO2 increases, the uptake of atmospheric CO2 becomes less significant. However, since melt ponds are continuously supplied by meltwater, their in situ pCO2 remains undersaturated with respect to the atmosphere, promoting a continuous but moderate uptake of CO2 (~ −1 mmol m−2 day−1) into the ocean. Considering the Arctic seasonal sea ice extent during the melt period (90 days), we estimate an uptake of atmospheric CO2 of −10.4 Tg of C yr−1. This represents an additional uptake of CO2 associated with Arctic sea ice that needs to be further explored and considered in the estimation of the Arctic Ocean's overall CO2 budget.
15
Schall, Christian, Klaus Gustav Heumann, Stephen De Mora e Peter A. Lee. "Biogenic brominated and iodinated organic compounds in ponds on the McMurdo Ice Shelf, Antarctica". Antarctic Science 8, n. 1 (marzo 1996): 45–48. http://dx.doi.org/10.1017/s0954102096000089.
Testo completoAbstract (sommario):
During January 1994 seven meltwater ponds on the McMurdo Ice Shelf were investigated for their content of biogenic iodinated and brominated volatile hydrocarbons. An efficient purge and trap system in combination with a powerful gas chromatographic separation and an electron capture detector achieved detection limits of 0.02–0.4 ng 1−1, depending on the different substances. The following compounds could be identified and quantified: CH3I, CH2I2, CH2C1I, CHBr3, CH2Br2, BrCH2CH2Br, CHBr2Cl, and CHBrCl2. This is the first time that 1,2–dibromoethane has been detected as a biogenic substance in the environment. In contrast to many other aquatic systems, where CH3I is found to be the most volatile iodine compound, CH2I2 showed the highest concentration in all ponds falling in the range of 5–20 ng 1−1. In three of seven ponds investigated, CH2CII was the second abundant iodinated substance. CHBr3 usually exhibited concentrations in the range of 2.5–8.6 ng 1−1. BrCH2CH2Br, previously not observed as a biogenic compound, was found to have concentrations similar to those of bromoform and even exceeded the bromoform content in two ponds and the CH2Br2 content in all ponds. Whether cyanobacteria, the dominant organisms in the ponds, are responsible for this distribution pattern must be clarified by further investigations.
16
Bates, N. R., R. Garley, K. E. Frey, K. L. Shake e J. T. Mathis. "Sea-ice melt CO<sub>2</sub>-carbonate chemistry in the western Arctic Ocean: meltwater contributions to air-sea CO<sub>2</sub> gas exchange, mixed layer properties and rates of net community production under sea ice". Biogeosciences Discussions 11, n. 1 (16 gennaio 2014): 1097–145. http://dx.doi.org/10.5194/bgd-11-1097-2014.
Testo completoAbstract (sommario):
Abstract. The carbon dioxide (CO2)-carbonate chemistry of sea-ice melt and co-located, contemporaneous seawater has rarely been studied in sea ice covered oceans. Here, we describe the CO2-carbonate chemistry of sea-ice melt (both above sea ice as "melt ponds" and below sea ice as "interface waters") and mixed layer properties in the western Arctic Ocean in the early summer of 2010 and 2011. At nineteen stations, the salinity (~ 0.5 to < 6.5), dissolved inorganic carbon (DIC; ~ 20 to < 550 μmol kg–1) and total alkalinity (TA; ~ 30 to < 500 μmol kg–1) of above-ice melt pond water was low compared to water in the underlying mixed layer. The partial pressure of CO2 (pCO2) in these melt ponds was highly variable (~ < 10 to > 1500 μatm) with the majority of melt ponds acting as potentially strong sources of CO2 to the atmosphere. The pH of melt pond waters was also highly variable ranging from mildly acidic (6.1 to 7) to slightly more alkaline than underlying seawater (8 to 10.7). All of observed melt ponds had very low (< 0.1) saturation states (Ω) for calcium carbonate (CaCO3) minerals such as aragonite (Ωaragonite). Our data suggests that sea ice generated "alkaline" or "acidic" melt pond water. This melt-water chemistry dictates whether the ponds are sources of CO2 to the atmosphere or CO2 sinks. Below-ice interface water CO2-carbonate chemistry data also indicated substantial generation of alkalinity, presumably owing to dissolution of calcium CaCO3 in sea ice. The interface waters generally had lower pCO2 and higher pH/Ωaragonite than the co-located mixed layer beneath. Sea-ice melt thus contributed to the suppression of mixed layer pCO2 enhancing the surface ocean's capacity to uptake CO2 from the atmosphere. Meltwater contributions to changes in mixed–layer DIC were also used to estimate net community production rates (mean of 46.9 ±29.8 g C m–2 for the early-season period) under sea-ice cover. Although sea-ice melt is a transient seasonal feature, above-ice melt pond coverage can be substantial (10 to > 50%) and under-ice interface melt water is ubiquitous during this spring/summer sea-ice retreat. Our observations contribute to growing evidence that sea-ice CO2-carbonate chemistry is highly variable and its contribution to the complex factors that influence the balance of CO2 sinks and sources (and thereby ocean acidification) is difficult to predict in an era of rapid warming and sea ice loss in the Arctic Ocean.
17
Paggi, J. C. "Feeding ecology ofBranchinecta gaini (crustacea: Anostraca) in ponds of south Shetland Islands, Antarctica". Polar Biology 16, n. 1 (gennaio 1996): 13–18. http://dx.doi.org/10.1007/bf02388730.
Testo completo
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Morris, Kim, e Martin O. Jeffries. "Seasonal contrasts in snow-cover characteristics on Ross Sea ice floes". Annals of Glaciology 33 (2001): 61–68. http://dx.doi.org/10.3189/172756401781818608.
Testo completoAbstract (sommario):
AbstractSnow-cover characteristics on ice floes in the Ross Sea, Antarctica, were examined during cruises in autumn 1998 and summer 1999. The autumn snow cover was shallower, colder and had higher and more variable salinity, and smaller single and composite grain-sizes than the summer snow cover. The autumn snow cover was dominated by rounded particles in chains of grains and clusters, while the summer snow cover was composed primarily of melt clusters. There was extensive flooding of the summer snow cover at the snow/ice interface. The summer snow cover was nearly isothermal and close to the melting point. It exhibited obvious signs of melting and refreezing in the form of ice lenses, pipes and superimposed ice, although no melt ponds were evident. Many of the ice lenses were located directly above the saline standing water found on most of the summer ice floes.
19
Hawes, Ian, Clive Howard-Williams e Brian Sorrell. "Decadal timescale variability in ecosystem properties in the ponds of the McMurdo Ice Shelf, southern Victoria Land, Antarctica". Antarctic Science 26, n. 3 (20 agosto 2013): 219–30. http://dx.doi.org/10.1017/s0954102013000576.
Testo completoAbstract (sommario):
AbstractMeltwater ponds are important biodiversity elements in continental Antarctica. Many occupy closed basins and are vulnerable to changes in the balance between water accrual, through melting of ice and snow, and water loss by ablation and evaporation. We use a two-decade long record of ponds on the McMurdo Ice Shelf to assess temporal variability in key limnological variables. Ponds underwent many-fold change in biologically conservative variables, such as conductivity, and changes were similar in ponds from different catchments but of comparable area. In contrast, biologically active variables (pH, inorganic nutrients and planktonic/benthic biomass) are buffered by in-pond processes and show consistency between years and no coherence across catchments. Coherent behaviour across catchments implies an overarching, climatic effect. However, we could identify no signature of summer air temperature or irradiance in pond dynamics, although winter snow deposition may leave a legacy of low conductivity to the following summer. While ponds are clearly affected by climate, our data show that ecosystem responses are complex and highlight the need for system-appropriate, long-term observation if directional environmental change is to be separated from inherent variability in systems that respond to multiple climatic variables and which have significant biological buffering capacity.
20
Broady, Paul A., e Richard N. Weinstein. "Algae, lichens and fungi in La Gorce Mountains, Antarctica". Antarctic Science 10, n. 4 (dicembre 1998): 376–85. http://dx.doi.org/10.1017/s0954102098000467.
Testo completoAbstract (sommario):
Two species of lichens, six cyanobacteria, one diatom, 10 chlorophytes and two mycelial fungi were found at La Gorce Mountains (86°30′S, 147°W) at an altitude of about 1750 m. The lichens Lecidea cancriformis and Carbonea vorticosa occurred at a single site which is the most southerly record of lichens. Thousands of small ponds covered extensive ice-cored moraine. Nine ponds sampled had about 30 cm of ice overlying about 26 cm of water and contained algal mats dominated by Phormidium autumnale and cf. Leptolyngbya fragilis. The very low conductivity waters had high nitrate and low dissolved reactive phosphorus concentrations. Of 124 soil samples, five contained visible algae. In 32 there were only microscopic growths but no algae were detected in 87 samples, possibly because of lack of water for much of summer. A visible mat dominated by Hammatoidea normanni occurred in a rock fissure at the lichen site. At Price Bluff, green patches of Desmococcus cf.olivaceus, up to 20 cm2, were scattered over the moraine. Growths were revealed at the soil–ice interface when overlying soil up to one centimetre thick was removed. It is suggested that although dispersal of algae from local populations may be readily achieved establishment of populations is a rare event outside the pond environment.
21
Fernández-Valiente, E., A. Quesada, C. Howard-Williams e I. Hawes. "N2-Fixation in Cyanobacterial Mats from Ponds on the McMurdo Ice Shelf, Antarctica". Microbial Ecology 42, n. 3 (1 ottobre 2001): 338–49. http://dx.doi.org/10.1007/s00248-001-1010-z.
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22
Jeffries, M. O., K. Schwartz e S. Li. "Arctic summer sea-ice SAR signatures, melt-season characteristics, and melt-pond fractions". Polar Record 33, n. 185 (aprile 1997): 101–12. http://dx.doi.org/10.1017/s003224740001442x.
Testo completoAbstract (sommario):
AbstractVariations in multiyear sea-ice backscatter from the synthetic aperture radar (SAR) aboard the ERS-1 satellite are interpreted in terms of melt-season characteristics (onset of melt in spring and of freeze-up in autumn, and the duration of the snow-decay period, the melt season, and the melt-pond season) from late winter to early autumn 1992 in two regions of the Arctic Ocean: the northeastern Beaufort Sea adjacent to the Queen Elizabeth Islands in the Canadian high Arctic and the western Beaufort Sea north of Alaska. In the northeastern Beaufort Sea, the onset of melt occurs later, and the periods of snow-cover decay and the occurrence of melt ponds are shorter than in the western Beaufort Sea. These melt-season characteristics of each area are consistent with previous observations that the northeastern Beaufort Sea has one of the most severe summer climates in the Arctic Ocean. A model, which assumes that the backscatter from multiyear floes is the sum of backscatter from bare ice and melt ponds, is used to derive the melt-pond fraction during the summer. The results show that melt-pond fractions decrease from an early-summer maximum of about 60% to a late-summer minimum around 10%. The magnitude of the melt-pond fractions and their decline during the summer is consistent with previous, more qualitative data. The SAR model, which gives melt-pond fractions with lower variability and less uncertainty than previous data, offers an improved approach to the reliable estimation of the areal extent of water on ice floes. Suggestions for further improvement of the model include accounting for the consequences of wind-speed variations, summer snowfall, and freeze/thaw cycles and their effects on melt-pond and ice-surface roughness.
23
Archer, Stephen D. J., Ian R. McDonald, Craig W. Herbold, Charles K. Lee, Thomas S. Niederberger e Craig Cary. "Temporal, regional and geochemical drivers of microbial community variation in the melt ponds of the Ross Sea region, Antarctica". Polar Biology 39, n. 2 (5 settembre 2015): 267–82. http://dx.doi.org/10.1007/s00300-015-1780-2.
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Archer, Stephen D. J., Ian R. McDonald, Craig W. Herbold e Stephen C. Cary. "Characterisation of bacterioplankton communities in the meltwater ponds of Bratina Island, Victoria Land, Antarctica". FEMS Microbiology Ecology 89, n. 2 (17 giugno 2014): 451–64. http://dx.doi.org/10.1111/1574-6941.12358.
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25
Vincent, W. F., e M. R. James. "Biodiversity in extreme aquatic environments: Lakes, ponds and streams of the Ross Sea sector, Antarctica". Biodiversity and Conservation 5, n. 11 (novembre 1996): 1451–71. http://dx.doi.org/10.1007/bf00051987.
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26
Rasmus, Kai, e Aike Beckmann. "The impact of global change on low-elevation blue-ice areas in Antarctica: a thermo-hydrodynamic modelling study". Annals of Glaciology 46 (2007): 50–54. http://dx.doi.org/10.3189/172756407782871774.
Testo completoAbstract (sommario):
AbstractIn Antarctica, low-elevation (<1000 m) blue-ice areas (LEBIAs) may experience melt–freeze cycles due to absorbed solar radiation and the small heat conductivity in the ice. In some cases, LEBIAs can contain significant amounts of subsurface liquid water. Since the spatial extent of blue-ice areas depends on climatic conditions, they have been seen as good indicators of warming in Antarctica. A two-dimensional (x-z) model has been developed to simulate the formation and water circulation in the subsurface ponds. The model results show that for a reasonable parameter set, the formation of liquid water within the ice can be reproduced. Vertical convection and a weak overturning circulation is generated which acts to stratify the fluid and transport warmer water downward, thereby causing additional melting at the base of the pond. In a multi-year integration, a global warming scenario mimicked by a decadal-scale increase (3˚C per 100 years) in air temperature, leads to a general increase in subsurface water volume and changes in pond shape and depth. Even before melting at the surface is reached, heat that accumulates below a certain depth can no longer be removed during winter and leads to disintegration of the ice.
27
Jungblut, Anne-Dorothee, Ian Hawes, Doug Mountfort, Bettina Hitzfeld, Daniel R. Dietrich, Brendan P. Burns e Brett A. Neilan. "Diversity within cyanobacterial mat communities in variable salinity meltwater ponds of McMurdo Ice Shelf, Antarctica". Environmental Microbiology 7, n. 4 (aprile 2005): 519–29. http://dx.doi.org/10.1111/j.1462-2920.2005.00717.x.
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28
Skácelová, Kateřina, e Miloš Barták. "Gradient of algal and cyanobacterial assemblages in a temporary lake with melting water at Solorina Valley, James Ross Island, Antarctica". Czech Polar Reports 4, n. 2 (1 giugno 2014): 185–92. http://dx.doi.org/10.5817/cpr2014-2-19.
Testo completoAbstract (sommario):
The aim of presented study is to contribute to species list of algae, cyanobacteria and diatoms from moist localities of James Ross Island, Solorina Valley (63° 53' S, 57° 48' W) in particular. In 2012, samples of microbiological mats were taken from a bottom of shallow depression close to a seashore line. The sampling site has been filled with melt-ing water from glacier for some weeks preceding the collection. On collection date, however it was dried out. The samples were analysed using optical microscopy approach after the transport of samples to Czech Republic (Masaryk University, Brno). Algal and cyanobacterial taxa forming the microbiological mats were determined according to their morphological characteristics and the frequencies of individual taxa occurrence evalu-ated. Species richness differed between individual sampling sites located across a shallow depression suggesting an ecological role of duration of stagnant water for bio-diversity in temporary freshwater ponds. Altogether, 37 algal and cyanobacterial taxa were found. While 23 taxa present in the centre of the depression, only 10 taxa were found close to the margin where the dry period was the longest.
29
Hall, Brenda, Gordon Bromley, John Stone e Howard Conway. "Holocene ice recession at Polygon Spur, Reedy Glacier, Antarctica". Holocene 27, n. 1 (28 luglio 2016): 122–29. http://dx.doi.org/10.1177/0959683616652708.
Testo completoAbstract (sommario):
The Holocene history of outlet glaciers affords information on the behavior and mechanisms controlling the extent of the East Antarctic Ice Sheet. Here, we present both new radiocarbon and recalculations of previously published cosmogenic exposure-age data that constrain Holocene ice dynamics along upper Reedy Glacier in the southernmost Transantarctic Mountains. Ice remained at or close to its last glacial maximum position until the early Holocene, at which time it underwent thinning. A period of apparent relative stability in the mid-Holocene led to the formation of ice-dammed proglacial ponds, as well as of moraines located roughly two-thirds of the distance from the maximum position to the present-day ice margin. Renewed thinning began after 3600 yr BP, with ice reaching present-day levels by 2400 yr BP. Ice variations along upper Reedy Glacier likely reflect the balance between upstream propagation of mechanical thinning events at the glacier mouth and regional accumulation changes.
30
Rasmus, Kai. "A thermo-hydrodynamic modelling study of an idealized low-elevation blue-ice area in Antarctica". Journal of Glaciology 55, n. 194 (2009): 1083–91. http://dx.doi.org/10.3189/002214309790794805.
Testo completoAbstract (sommario):
AbstractLow-elevation blue-ice areas in Antarctica can contain significant amounts of subsurface liquid water during summer and may experience internal melt–freeze cycles due to absorption of shortwave radiation. An existing 2-D (x-z) model has been used to study the phenomenon and this is improved by changing the lower boundary condition from a no-flux condition to one that lets heat through, and by changing the bulk optical properties to spectral values. Both changes made the model more realistic. The optical and thermal boundary conditions, together with the optical attenuation coefficient, have a large effect on the amount of water produced in the ice. Our results show that if the lower boundary condition is changed from no flux to radiating, subsurface melting is reduced dramatically. Using a spectral albedo produces less melting than using a corresponding bulk albedo, the other variables left unchanged. If optical properties are changed to spectral values, the melting is different than using bulk values. If the linear extent of the blue-ice area is <0.6 m, subsurface melting is diminished. We found the spatial variability of snow has a significant effect on subsurface melting. Subsurface melting was found to be impossible for albedos >0.7 and the subsurface ponds can persist over the winter if the albedo is <0.4.
31
Howard-Williams, C., R. Pridmore, M. T. Downes e W. F. Vincent. "Microbial biomass, photosynthesis and chlorophyll a related pigments in the ponds of the McMurdo Ice Shelf, Antarctica". Antarctic Science 1, n. 2 (giugno 1989): 125–31. http://dx.doi.org/10.1017/s0954102089000192.
Testo completoAbstract (sommario):
The extensive ablation zone on the McMurdo Ice Shelf (78°S, 165°30′E) contains numerous ponds that are lined with benthic mats of cyanobacteria and associated micro-organisms. The photoautotrophic biomass content of these mats was examined in six contrasting ponds. Particulate carbon contributed only 3.2% of the mat dry weight, with C:N ratios generally less than 20:1. The chlorophyll a content was low relative to carbon (chlorophylla : C<0.01). Analysis of the mats by high performance liquid chromatography [HPLC] showed that the pigment fraction assayed spectrophotometrically as chlorophyll a contained large quantities (up to 70%) of the degradation product chlorophyllide a and the epimer chlorophyll a'. Photosynthetic rates per unit chlorophyll a[HPLC] were extremely slow: <0.1 mg C (mg Chla)−1, less than one tenth the rates recorded in the overlying phytoplankton community. These analyses indicate that in the ice pond benthic mats most of the dry weight is inorganic, most of the organic carbon is non-chlorophyll-containing material, and much of the chlorophyll a is not photosynthetically active. Cold temperatures and the associated low activity of herbivores and detritivores may contribute towards this preservation of inactive chlorophyll a on the McMurdo Ice Shelf, and perhaps in similar benthic mats in the lakes and streams of southern Victoria Land.
32
Rochera, Carlos, e Antonio Camacho. "Limnology and Aquatic Microbial Ecology of Byers Peninsula: A Main Freshwater Biodiversity Hotspot in Maritime Antarctica". Diversity 11, n. 10 (21 ottobre 2019): 201. http://dx.doi.org/10.3390/d11100201.
Testo completoAbstract (sommario):
Here we present a comprehensive review of the diversity revealed by research in limnology and microbial ecology conducted in Byers Peninsula (Livingston Island, South Shetland Islands, Antarctica) during the last two decades. The site constitutes one of the largest ice-free areas within the Antarctic Peninsula region. Since it has a high level of environmental protection, it is less human-impacted compared to other sites within the South Shetland archipelago. The main investigations in Byers Peninsula focused on the physical and chemical limnology of the lakes, ponds, rivers, and wetlands, as well as on the structure of their planktonic and benthic microbial communities, and on the functional ecology of the microbial food webs. Lakes and ponds in Byers range along a productivity gradient that extends from the less productive lakes located upland to the eutrophic coastal lakes. Their planktonic assemblages include viruses, bacteria, a metabolically diverse community of protists (i.e., autotrophs, heterotrophs, and mixotrophs), and a few metazooplankton species. Most of the studies conducted in the site demonstrate the strong influence of the physical environment (i.e., temperature, availability of light, and water) and nutrient availability in structuring these microbial communities. However, top-down biotic processes may occur in summer, when predation by zooplankton can exert a strong influence on the abundance of protists, including flagellates and ciliated protozoa. As a consequence, bacterioplankton could be partly released from the grazing pressure exerted by these protists, and proliferates fueled by external nutrient subsidies from the lake’s catchment. As summer temperatures in this region are slightly above the melting point of water, biotic processes, such as those related to the productivity of lakes during ice-free periods, could become even more relevant as warming induced by climate change progresses. The limnological research carried out at the site proves that Byers Peninsula deserves special attention in the framework of the research in extreme environments. Together with nearby sites, such as Signy Island, Byers Peninsula comprises a featuring element of the Maritime Antarctic region that represents a benchmark area relative to the global distribution and diversity of aquatic microorganisms.
33
Mieczan, Tomasz, e Małgorzata Adamczuk. "Ecology of Ciliates in Microbial Mats in Small Ponds: Relationship to Environmental Parameters (King George Island, Maritime Antarctica)". Annales Zoologici Fennici 53, n. 3-4 (agosto 2016): 201–14. http://dx.doi.org/10.5735/086.053.0409.
Testo completo
34
Mrozińska, T., M. Olech e A. Massalski. "Algae of ponds and a stream on moraines of Ecology Glacier (King George Island, South Shetland Islands, Antarctica)". Nova Hedwigia 67, n. 1-2 (28 settembre 1998): 169–88. http://dx.doi.org/10.1127/nova.hedwigia/67/1998/169.
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35
Flexas, Mar M., Mariano R. Arias e Miguel A. Ojeda. "Hydrography and dynamics of Port Foster, Deception Island, Antarctica". Antarctic Science 29, n. 1 (3 ottobre 2016): 83–93. http://dx.doi.org/10.1017/s0954102016000444.
Testo completoAbstract (sommario):
AbstractThe circulation and water masses of Port Foster, Deception Island, were studied using conductivity-temperature-depth stations inside and outside the semi-enclosed bay and an array of bottom temperature sensors moored around the perimeter of the bay over two weeks in the summer of 2012. Inside Port Foster, the water column is divided into two layers separated by a temperature-forced, seasonal pycnocline at ~40–60 m. The circulation of the upper layer is in an anticlockwise direction, with mean geostrophic currents of ~0.04–0.10 ms-1. The lower layer, from ~60 m to the seabed, shows coastal-trapped waves travelling in a clockwise direction, possibly triggered by local wind gusts. Local sea ice melt in areas surrounding the underwater hot springs of Pendulum Cove appears as a fresh, warm anomaly down to 30 m.
36
de los Ríos, Asunción, Carmen Ascaso, Jacek Wierzchos, Eduardo Fernández-Valiente e Antonio Quesada. "Microstructural Characterization of Cyanobacterial Mats from the McMurdo Ice Shelf, Antarctica". Applied and Environmental Microbiology 70, n. 1 (gennaio 2004): 569–80. http://dx.doi.org/10.1128/aem.70.1.569-580.2004.
Testo completoAbstract (sommario):
ABSTRACT The three-dimensional structures of two types of cyanobacterium-dominated microbial mats from meltwater ponds on the McMurdo Ice Shelf were as determined by using a broad suite of complementary techniques, including optical and fluorescence microscopy, confocal scanning laser microscopy, scanning electron microscopy with back-scattered electron-imaging mode, low-temperature scanning electron microscopy, and microanalyitical X-ray energy dispersive spectroscopy. By using a combination of the different in situ microscopic techniques, the Antarctic microbial mats were found to be structures with vertical stratification of groups of cyanobacteria and mineral sediments, high contents of extracellular polymeric substances, and large void spaces occupied by water. In cyanobacterium-rich layers, heterocystous nostocalean and nonheterocystous oscillatorialean taxa were the most abundant taxa and appeared to be intermixed with fine-size deposits of epicellular silica and calcium carbonate. Most of the cyanobacterial filaments had similar orientations in zones without sediment particles, but thin filaments were tangled among thicker filaments. The combination of the microscopic techniques used showed the relative positions of biological and mineral entities within the microbial mats and enabled some speculation about their interactions.
37
Gore, Damian B. "Ice-damming and fluvial erosion in the Vestfold Hills, East Antarctica". Antarctic Science 4, n. 2 (giugno 1992): 227–34. http://dx.doi.org/10.1017/s0954102092000348.
Testo completoAbstract (sommario):
An ice dam with a former impoundment volume of 1.1 × 106 m3 is reported from the Vestfold Hills, East Antarctica. The ice of the dam was derived from wind-drifted snow subsequently changed into ice by normal summer melt and freeze processes. The reformation (after 1979 and 1987) and failure of this ice dam (during 1987 and 1990) indicates the potential for the release of geomorphologically significant flows in a polar climate. The origin of a nearby fluvially eroded channel is attributed to the release of an ice-dammed impoundment. The potential of such flows for reworking glacial debris may be important when considering the sedimentology of former proglacial areas.
38
Schnack-Schiel, Sigrid B., David N. Thomas, Christian Haas, Gerhard S. Dieckmann e Ruth Alheit. "The occurrence of the copepods Stephos longipes (Calanoida) and Drescheriella glacialis (Harpacticoida) in summer sea ice in the Weddell Sea, Antarctica". Antarctic Science 13, n. 2 (giugno 2001): 150–57. http://dx.doi.org/10.1017/s0954102001000232.
Testo completoAbstract (sommario):
In January to March 1997, a RV Polarstern cruise that transected the Weddell Sea resulted in samples being taken in thick pack ice in the south-eastern Weddell Sea and then along the marginal ice edge towards the Antarctic Peninsula. Several ice types were thus sampled over a wide geographic area during late summer/early autumn. Common features of the first warm period was the occurrence of surface ponds, and that many floes had quasi-continuous horizontal gaps, underlying a layer of ice and metamorphic snow. With the onset of cold air temperatures in late February the gaps rapidly refroze. The calanoid copepod Stephos longipes occurred in all habitats encountered and showed highest numbers in the surface ice in summer, in the gap water during both seasons and in the refrozen gap water in autumn. Nauplii outnumbered copepodids in the surface ice and refrozen gap water, while in the gap water copepodids, mainly stages CI–CIII in summer and CII–CIV in autumn, comprised about 70% of the total population. The harpacticoid species Drescheriella glacialis did not occur in all habitats and was missing in surface ponds and new ice. Nauplii of D. glacialis were rarely found in gap water, but predominated in the refrozen gaps.
39
Rochera, Carlos, Juan Antonio Villaescusa, David Velázquez, Eduardo Fernández-Valiente, Antonio Quesada e Antonio Camacho. "Vertical structure of bi-layered microbial mats from Byers Peninsula, Maritime Antarctica". Antarctic Science 25, n. 2 (20 marzo 2013): 270–76. http://dx.doi.org/10.1017/s0954102012000983.
Testo completoAbstract (sommario):
AbstractA summer study of the vertical structure of bi-layered microbial mats was carried out on Byers Peninsula (Livingston Island, South Shetland Islands). These benthic communities had a common basic structure that consisted of two distinct layers differing in composition, morphology and colour. Our sampling focused on mats showing more layering, which thrived over moist soils and at the bottom of ponds. The photosynthetic pigments analysis performed by high-performance liquid chromatography demonstrated a major occurrence of cyanobacteria and diatoms on these mats, the former being more abundant in relative terms on the surface and composed by morphospecies grouping into orders Oscillatoriales, Nostocales and Chroococcales. The areal chlorophyll a concentrations were slightly higher in the deeper layer although not significantly. Our microscopic and chemical analyses showed that non-active biomass accumulates at the surface. Hence, the upper layers showed the sheath pigment scytonemin and higher amounts of exopolysaccharides, as a strategy to cope with environmental stress. On the other hand, the basal layer was composed of more active photosynthetic microbiota, which also revealed a more balanced stoichiometry. Here we exemplify how environmental stresses are potentially overcome by physiological mechanisms developed by microbial mats which also shape their vertical structure.
40
Esposito, R. M. M., S. A. Spaulding, D. M. McKnight, B. Van de Vijver, K. Kopalová, D. Lubinski, B. Hall e T. Whittaker. "Inland diatoms from the McMurdo Dry Valleys and James Ross Island, Antarctica". Botany 86, n. 12 (dicembre 2008): 1378–92. http://dx.doi.org/10.1139/b08-100.
Testo completoAbstract (sommario):
Diatom taxa present in the inland streams and lakes of the McMurdo Dry Valleys and James Ross Island, Antarctica, are presented in this paper. A total of nine taxa are illustrated, with descriptions of four new species ( Luticola austroatlantica sp. nov., Luticola dolia sp. nov., Luticola laeta sp. nov., Muelleria supra sp. nov.). In the perennially ice-covered lakes of the McMurdo Dry Valleys, diatoms are confined to benthic mats within the photic zone. In streams, diatoms are attached to benthic surfaces and within the microbial mat matrix. One species, L. austroatlantica, is found on James Ross Island, of the southern Atlantic archipelago, and the McMurdo Dry Valleys. The McMurdo Dry Valley populations are at the lower range of the size spectrum for the species. Streams flow for 6–10 weeks during the austral summer, when temperatures and solar radiation allow glacial ice to melt. The diatom flora of the region is characterized by species assemblages favored under harsh conditions, with naviculoid taxa as the dominant group and several major diatom groups conspicuously absent.
41
Carmichael, Joshua D., Erin C. Pettit, Matt Hoffman, Andrew Fountain e Bernard Hallet. "Seismic multiplet response triggered by melt at Blood Falls, Taylor Glacier, Antarctica". Journal of Geophysical Research: Earth Surface 117, F3 (10 luglio 2012): n/a. http://dx.doi.org/10.1029/2011jf002221.
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FANG, AIMIN, XIAOHAN LIU, XIAOLI LI, FEIXIN HUANG e LIANGJUN YU. "Cenozoic glaciogenic sedimentary record in the Grove Mountains of East Antarctica". Antarctic Science 17, n. 2 (giugno 2005): 237–40. http://dx.doi.org/10.1017/s0954102005002646.
Testo completoAbstract (sommario):
During fieldwork of the 1998–99 and 1999–2000 Chinese National Antarctic Research Expedition (CHINARE), three different kinds of Cenozoic sedimentary record were found in the Grove Mountains, which are in East Antarctica about 450km inland of Prydz Bay. These consist of (1) glaciogenic sedimentary erratics found in the moraine banks in the central area of Grove Mountains, which can be subdivided into four types according to different degrees of lithification as well as differences in inner structure and include in-situ diamicts; (2) palaeosols found in several small depressions in the southern slope of the Mount Harding; and (3) different kinds of glacial moraine floating on the surface of blue ice or around the foot of some nunataks. Preliminary results suggest that the in situ glaciogenic sediments were formed in the ice-sheet frontal area by the interaction of glacial movement and ice sheet melt water under climatic conditions warmer than today.
43
Podgorny, Igor A., e Thomas C. Grenfell. "Partitioning of solar energy in melt ponds from measurements of pond albedo and depth". Journal of Geophysical Research: Oceans 101, n. C10 (15 ottobre 1996): 22737–48. http://dx.doi.org/10.1029/96jc02123.
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Schroeter, Burkhard, T. G. Allan Green, Ana Pintado, Roman Türk e Leopoldo G. Sancho. "Summer activity patterns for mosses and lichens in Maritime Antarctica". Antarctic Science 29, n. 6 (1 agosto 2017): 517–30. http://dx.doi.org/10.1017/s095410201700027x.
Testo completoAbstract (sommario):
AbstractWithin Antarctica there are large gradients both in climate and in vegetation which offer opportunities to investigate links between the two. The activity (% total time active) of lichens and bryophytes in hydric and xeric environments was monitored at Livingston Island (62°39'S). This adds a northern site with a maritime, cloudy climate to previous studies in the southern Antarctic Peninsula and the Dry Valleys (78°S). Annual activity increases northwards from less than 1% to nearly 100%. There is a major and consistent difference between hydric sites which, with snow melt, can be 100% active in summer months even in the Dry Valleys, and xeric sites which, depending on precipitation, rarely exceed 80% activity even at Livingston Island. Mosses dominate hydric sites and lichens the xeric sites all along the gradient. Mean temperatures when active are 2–4°C at all sites, as liquid water is required. Light is a potential major stress reaching 880 µmol m-2s-1when active in continental sites. The lack of extremes in temperatures and light combined with high activity levels means that summer at Livingston Island is one of the better sites for lichen and bryophyte growth in the world.
45
NICACIO, GILBERTO, WILLIAM SEVERI e ULISSES PINHEIRO. "New species of Radiospongilla (Porifera: Spongillidae) from Brazilian inland waters". Zootaxa 3132, n. 1 (15 dicembre 2011): 56. http://dx.doi.org/10.11646/zootaxa.3132.1.2.
Testo completoAbstract (sommario):
Radiospongilla Penney & Racek, 1968, characterized by gemmoscleres radially arranged on gemmules and absence of microscleres, is widely distributed in the world across all zoogeographical regions except for Antarctica. In the Neotropical Region only two species are known so far: R. crateriformis (Potts, 1882) and R. amazonensis Volkmer-Ribeiro & Maciel, 1983. Here we describe a new species of Radiospongilla, R. inesi sp. nov., from 28 specimens collected between May 2007 to April 2010 from channels and ponds at the Aquaculture Station of Universidade Federal Rural de Pernambuco, Rio do Prata Basin, Recife, Pernambuco State, Brazil. This new species differs from other species of Radiospongilla from South America in the morphology of its megascleres and gemmoscleres.
46
CURTIS, MICHAEL L., e TEAL R. RILEY. "Mobilization of fluidized sediment during sill emplacement, western Dronning Maud Land, East Antarctica". Antarctic Science 15, n. 3 (settembre 2003): 393–98. http://dx.doi.org/10.1017/s0954102003001408.
Testo completoAbstract (sommario):
Large mafic sills in the Ahlmannryggen region of western Dronning Maud Land were intruded into partially lithified sediments of the mid-Proterozoic Ritscherflya Supergroup. Clastic sedimentary dykes intruding the thick mafic sills have been identified, and show evidence for fluidization of the partially lithified sediments. Previous work had demonstrated in situ fluidization and localized anatectic melting. This study demonstrates mobilization of the fluidized sediments, with penetration at least 50 m into the fractured, intruding sill. Physical features within the clastic dykes (e.g. sediment balls, flame structures) suggest that the sediments were largely unconsolidated, or at most only partially lithified. The presence of a thin zone of anatectic melt along the dyke—sill contact suggests that the mafic sill was still hot (c. 700°C) at the time of sedimentary dyke injection.
47
Novis, Phil M., e Rob D. Smissen. "Two genetic and ecological groups of Nostoc commune in Victoria Land, Antarctica, revealed by AFLP analysis". Antarctic Science 18, n. 4 (14 novembre 2006): 573–81. http://dx.doi.org/10.1017/s0954102006000617.
Testo completoAbstract (sommario):
Microscopy, DNA sequencing, and amplified fragment length polymorphism (AFLP) were used to examine variation within Nostoc commune from collections between 72 and 78°S in Victoria Land, Antarctica. Although there is considerable bias of collected material towards southern latitudes, and this material varies greatly in age (collected between 1984 and 2004), an important new phylogeographic pattern was found. DNA sequencing of the tRNAleu(UAA) region, used recently to define form species N. commune, revealed little variation between collections. AFLP analysis, however, split the collected material according to habitat (irrigated soil communities versus ponds), rather than latitude. These results suggest that environmental factors linked to latitude are not the greatest drivers of genetic variation in Victoria Land. These may operate at a lower level but would require intensive sampling within narrowly defined habitat types at a range of latitudes to uncover. We advocate extensive sampling across local environmental gradients based on water availability, comparative culturing, and development of sequence characterised amplified regions (SCARs) across a range of latitudes in future seasons of the Latitudinal Gradient Project.
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de Pablo, M. A., J. J. Blanco, A. Molina, M. Ramos, A. Quesada e G. Vieira. "Interannual active layer variability at the Limnopolar Lake CALM site on Byers Peninsula, Livingston Island, Antarctica". Antarctic Science 25, n. 2 (20 marzo 2013): 167–80. http://dx.doi.org/10.1017/s0954102012000818.
Testo completoAbstract (sommario):
AbstractIn order to monitor the evolution of the active layer in the South Shetland Islands, in February 2009 we established a new Circumpolar Active Layer Monitoring (CALM) site in the Limnopolar Lake basin on Byers Peninsula, Livingston Island. We monitored air, surface and ground (two boreholes of 135 and 80 cm deep) temperatures and Active Layer Thickness (ALT) was measured by mechanical probing in early February 2009, 2010 and 2011. The mean ALT was 44 cm with a range of about 92 cm, but where permafrost existed it was deeper than 1.0 m, as could be inferred from the borehole temperatures. ALT at this site was very dependent on air temperature and snow cover thickness, the ALT spatial distribution presenting the same pattern as soil penetration resistance, and higher values ALT coinciding with sites where patterned ground, ponds, and a near surface ground water saturation were observed. Additionally, ground temperature data provided an excellent tool for understanding the relationship between the ALT measured during the thaw season and the thermal evolution of the ground throughout the year.
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Sommers, M. D., L. A. Randall e R. M. R. Barclay. "Effects of environmental variables on the calling behaviour of Northern Leopard Frogs (Lithobates pipiens) in Alberta, Canada". Canadian Journal of Zoology 96, n. 2 (febbraio 2018): 163–69. http://dx.doi.org/10.1139/cjz-2016-0239.
Testo completoAbstract (sommario):
Breeding behaviour of Temperate Zone amphibians is influenced by environmental variables, but the initiation of calling (phenology) and influences on calling activity may vary with species and region. We investigated the influence of the timing of ice melt, water temperature, and photoperiod on the breeding phenology of the Northern Leopard Frog (Lithobates pipiens (Schreber, 1782)) in southern Alberta, Canada, using automated recording units. We also examined the influence of wind speed, relative humidity, water temperature, and time of day on calling activity. The initiation of calling varied by 13 days at our three sites, suggesting that calling was influenced more by water temperature and timing of ice melt than photoperiod. Calling was first observed 8–11 days after ice melt at water temperatures of 7.5–8 °C at our sites. No calling was detected at water temperature <5 °C. We recorded nocturnal and diurnal calling at all sites; >50% of calling was diurnal, even on days with warm overnight temperatures. Calling activity was influenced by time of day, water temperature, wind, and relative humidity. Our results suggest that date of initiation of calling varies considerably among breeding ponds and that the time of day of peak calling varies with both site and water temperature.
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Filler, D. M., C. M. Reynolds, I. Snape, A. J. Daugulis, D. L. Barnes e P. J. Williams. "Advances in engineered remediation for use in the Arctic and Antarctica". Polar Record 42, n. 2 (aprile 2006): 111–20. http://dx.doi.org/10.1017/s003224740500505x.
Testo completoAbstract (sommario):
Creative remediation schemes have been implemented with success at petroleum-contaminated sites in Alaska and Canada during the past decade. Contaminated media have been landfarmed, amended with fertilizers, augmented with microbial products, and manipulated with engineered systems. Phytoremediation developments and use of biodegradable synthetic and polymeric resins for potential use with petroleum and xenobiotic contaminants are on the horizon. Treatment of supra-permafrost water and melt-water runoff with permeable reactive barriers and partitioning bioreactors is now possible. Cost and time limitations will likely continue to drive remediation decisions in the Arctic. Environmental policy, environmental constraints, and cost will dictate what technologies are appropriate for Antarctic clean-up, although the pressure of time is less acute because land transfer and liability are not drivers. This paper discusses some recent advances in remediation engineering for use in polar regions. Conceptual models are presented, and case study treatment costs and durations are highlighted to aid environmental decision-making.