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  • 1
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    Bedmap2: improved ice bed, surface and thickness datasets for Antarctica (2013)
    In:  EPIC3The Cryosphere, 7, pp. 375-393
    Details
    Publication Date: 2017-10-17
    Description: We present Bedmap2, a new suite of gridded products describing surface elevation, ice-thickness and the seafloor and subglacial bed elevation of the Antarctic south of 60� S. We derived these products using data from a variety of sources, including many substantial surveys completed since the original Bedmap compilation (Bedmap1) in 2001. In particular, the Bedmap2 ice thickness grid is made from 25 million measurements, over two orders of magnitude more than were used in Bedmap1. In most parts of Antarctica the subglacial landscape is visible in much greater detail than was previously available and the improved datacoverage has in many areas revealed the full scale of mountain ranges, valleys, basins and troughs, only fragments of which were previously indicated in local surveys. The derived statistics for Bedmap2 show that the volume of ice contained in the Antarctic ice sheet (27 million km3) and its potential contribution to sea-level rise (58 m) are similar to those of Bedmap1, but the mean thickness of the ice sheet is 4.6% greater, the mean depth of the bed beneath the grounded ice sheet is 72m lower and the area of ice sheet grounded on bed below sea level is increased by 10 %. The Bedmap2 compilation highlights several areas beneath the ice sheet where the bed elevation is substantially lower than the deepest bed indicated by Bedmap1. These products, along with grids of data coverage and uncertainty, provide new opportunities for detailed modelling of the past and future evolution of the Antarctic ice sheets.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
    facet.materialart.
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    Bedmap2: improved ice bed, surface and thickness datasets for Antarctica (2013)
    Copernicus Gesellschaft GMBH
    Details
    Publication Date: 2024-04-17
    Description: We present Bedmap2, a new suite of gridded products describing surface elevation, ice-thickness and the seafloor and subglacial bed elevation of the Antarctic south of 60 S. We derived these products using data from a variety of sources, including many substantial surveys completed since the original Bedmap compilation (Bedmap1) in 2001. In particular, the Bedmap2 ice thickness grid is made from 25 million measurements, over two orders of magnitude more than were used in Bedmap1. In most parts of Antarctica the subglacial landscape is visible in much greater detail than was previously available and the improved datacoverage has in many areas revealed the full scale of mountain ranges, valleys, basins and troughs, only fragments of which were previously indicated in local surveys. The derived statistics for Bedmap2 show that the volume of ice contained in the Antarctic ice sheet (27 million km3) and its potential contribution to sea-level rise (58 m) are similar to those of Bedmap1, but the mean thickness of the ice sheet is 4.6% greater, the mean depth of the bed beneath the grounded ice sheet is 72m lower and the area of ice sheet grounded on bed below sea level is increased by 10 %. The Bedmap2 compilation highlights several areas beneath the ice sheet where the bed elevation is substantially lower than the deepest bed indicated by Bedmap1. These products, along with grids of data coverage and uncertainty, provide new opportunities for detailed modelling of the past and future evolution of the Antarctic ice sheets.
    Description: Published
    Description: 375–393
    Description: 1.8. Osservazioni di geofisica ambientale
    Description: 3.8. Geofisica per l'ambiente
    Description: JCR Journal
    Description: open
    Keywords: Antarctic bedrock topography ; Antarctic mass balance ; 01. Atmosphere::01.01. Atmosphere::01.01.02. Climate ; 02. Cryosphere::02.02. Glaciers::02.02.04. Ice ; 02. Cryosphere::02.02. Glaciers::02.02.05. Ice dynamics ; 02. Cryosphere::02.02. Glaciers::02.02.06. Mass balance
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
    Electronic Resource
    Electronic Resource
    Determination of Hydroperoxides in Petroleum Products. (1953)
    s.l. : American Chemical Society
    Analytical chemistry 25 (1953), S. 923-925 
    Details
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ac60078a020
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  • 4
    Electronic Resource
    Electronic Resource
    Round Table Discussion. Direct Determination of Oxygen in Organic Compounds (1951)
    s.l. : American Chemical Society
    Analytical chemistry 23 (1951), S. 530-533 
    Details
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ac60051a042
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  • 5
    Electronic Resource
    Electronic Resource
    Direct Determination of Oxygen in Organic Substances (1954)
    s.l. : American Chemical Society
    Analytical chemistry 26 (1954), S. 600-602 
    Details
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ac60087a064
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  • 6
    Electronic Resource
    Electronic Resource
    Marine diatoms grown in chemostats under silicate or ammonium limitation. III. Cellular chemical composition and morphology of Chaetoceros debilis, Skeletonema costatum, and Thalassiosira gravida (1977)
    Springer
    Marine biology 43 (1977), S. 19-31 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Three marine diatoms, Skeletonema costatum, Chaetoceros debilis, and Thalassiosira gravida were grown under no limitation and ammonium or silicate limitation or starvation. Changes in cell morphology were documented with photomicrographs of ammonium and silicate-limited and non-limited cells, and correlated with observed changes in chemical composition. Cultures grown under silicate starvation or limitation showed an increase in particulate carbon, nitrogen and phosporus and chlorophyll a per unit cell volume compared to non-limited cells; particulate silica per cell volume decreased. Si-starved cells were different from Si-limited cells in that the former contained more particulate carbon and silica per cell volume. The most sensitive indicator of silicate limitation or starvation was the ratio C:Si, being 3 to 5 times higher than the values for non-limited cells. The ratios Si:chlorophyll a and S:P were lower and N:Si was higher than non-limited cells by a factor of 2 to 3. The other ratios, C:N, C:P, C:chlorophyll a, N:chlorophyll a, P:chlorophyll a and N:P were considered not to be sensitive indicators of silicate limitation or starvation. Chlorophyll a, and particulate nitrogen per unit cell volume decreased under ammonium limitation and starvation. NH4-starved cells contained more chlorophyll a, carbon, nitrogen, silica, and phosphorus per cell volume than NH4-limited cells. N:Si was the most sensitive ratio to ammonium limitation or starvation, being 2 to 3 times lower than non-limited cells. Si:chlorophyll a, P:chlorophyll a and N:P were less sensitive, while the ratios C:N, C:chlorophyll a, N:chlorophyll a, C:Si, C:P and Si:P were the least sensitive. Limited cells had less of the limiting nutrient per unit cell volume than starved cells and more of the non-limiting nutrients (i.e., silica and phosphorus for NH4-limited cells). This suggests that nutrient-limited cells rather than nutrient-starved cells should be used along with non-limited cells to measure the full range of potential change in cellular chemical composition for one species under nutrient limitation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392568
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  • 7
    Electronic Resource
    Electronic Resource
    Interactions of inorganic nitrogen in the uptake and assimilation by marine phytoplankton (1977)
    Springer
    Marine biology 39 (1977), S. 221-232 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of ambient ammonium concentration on the nitrate uptake rate of marine phytoplankton was investigated. These studies consisted of laboratory experiments using unialgal species and field experiments using natural phytoplankton communities. In laboratory experiments, ammonium suppressed the uptake rates of nitrate and nitrite. Approximately 30 min were required for ammonium to exhibit its fully inhibitory effect on nitrate uptake. At high ammonium concentration (〉3 μg-at/l), a residual nitrate uptake rate of approximately 0.006 h-1 was observed. When the ambient ammonium concentration was reduced to a value less than 1 μg-at/l, the suppressed nitrate uptake rate subsequently attained a value comparable to that observed before the addition of ammonium. A range of 25 to 60% reduction in the nitrate uptake rate of natural phytoplankton communities was observed at ambient ammonium concentrations of ∼1.0 μg-at/l. A mechanism is proposed for the suppression of nitrate uptake rate by ammonium through feedback control of the nitrate permease system and/or the nitrate reductase enzyme system. The feedback control is postulated to be regulated by the level of total amino acids in the cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00390996
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  • 8
    Electronic Resource
    Electronic Resource
    Marine diatoms grown in chemostats under silicate or ammonium limitation. IV. Transient response of Chaetoceros debilis, Skeletonema costatum, and Thalassiosira gravida to a single addition of the limiting nutrient (1977)
    Springer
    Marine biology 43 (1977), S. 33-43 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The kinetic response of ammonium- or silicate-limited and ammonium- or silicatestarved populations of Chaetoceros debilis, Skeletonema costatum, and Thalassiosira gravida was determined by a single addition of the limiting nutrient to a steady-state culture and subsequent monitoring of the nutrient disappearance of the limiting and non-limiting nutrients at frequent time intervals. The kinetic response of nonlimited (nutrient) populations of these three species was also determined. Three distinct modes of the uptake of the limiting nutrient were observed for ammonium-or silicate-limited populations of these three species, surge uptake (V s ), internally (cellular) controlled uptake (V i ), and externally (ambient limiting nutrient concentration) controlled uptake (V e ). Non-limited populations did not exhibit the three distinct segments of uptake, V s , V i and V e . Estimates of the maximal uptake rate (V max) and the Michaelis constant (K s ) were obtained from nutrient-limited populations during the V e segment of the uptake curve. Pooled values of V e for the three ammonium-limited populations yielded V max and K s estimates of 0.16 h-1 and 0.5 μg-at NH4−N l-1. Kinetic data derived from the V e segment of the uptake curve for silicate-limited populations yielded different values of V max and K s for each of the three species. In a number of parameters that were measured, T. gravida was clearly different from C. debilis and S. costatum and its recovery from nutrient starvation was the slowest. Recovery of all species from silicate limitation or starvation was slower than from ammonium limitation or starvation. Ammonium-starved populations maintained a maximal uptake rate at a substrate concentration an order of magnitude lower (≈0.1 μg-at NH4−N l-1) than that observed for NH4-limited populations (≈1.0 μg-at NH4−N l-1). Adaptation to the severity of the nutrient limitation occurred as changes in the magnitude of cellular characteristics, such as short-term uptake potential (V s ) and affinity for the substrate (K s ). The consequence of these results are discussed in terms of another possible mechanism to explain changes in species composition and succession in nutrient-depleted environments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392569
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  • 9
    Electronic Resource
    Electronic Resource
    Interactions between nitrate and ammonium uptake: variation with growth rate, nitrogen source and species (1984)
    Springer
    Marine biology 79 (1984), S. 151-164 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The interaction between nitrate and ammonium uptake was examined as a function of preconditioning growth rate and nitrogen source by adding nitrate, ammonium, or both to nitrogen-sufficient,-deficient, and-starvedSkeletonema costatum (Grev.) Cleve and nitrogen-deficientChaetoceros debilis Cleve. By simultaneously measuring the internal accumulation of intermediates of nitrogen assimilation and the rates of nitrogen assimilation, the metabolic control of nitrogen uptake could be assessed. After the simultaneous addition of nitrate and ammonium to culture, both nitrate and ammonium uptake rates were decreased in comparison with the rates observed when each was added alone, although nitrate uptake was usually decreased more than ammonium uptake. Since both nitrate and ammonium uptake rates vary with time, preconditioning growth conditions, nitrogen sources present, and species, it was necessary to use several different indices to quantify inhibition. In general, ammonium inhibition of nitrate uptake inS. costatum was greatest in cultures preconditioned to ammonium and those at low growth rates, whereas ammonium uptake was inhibited most in cultures preconditioned to nitrate. In nitrogen-deficientC. debilis, nitrate uptake was more inhibited by ammonium, but uptake returned to normal rates more quickly than inS. costatum, whereas inhibition of ammonium uptake was similar. These results explain why the interaction between nitrate and ammonium uptake in the field can be so variable. Inhibition of uptake is not controlled by internal ammonium or total amino acids, nor is it related to the inability to reduce nitrate. Instead, inhibition must be determined in part by the external concentration of nitrogen compounds and in part by some intermediate(s) of nitrogen assimilation present inside the cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00951824
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  • 10
    Electronic Resource
    Electronic Resource
    Marine diatoms grown in chemostats under silicate or ammonium limitation. I. Cellular chemical composition and steady-state growth kinetics of Skeletonema costatum (1976)
    Springer
    Marine biology 35 (1976), S. 177-186 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Skeletonema costatum was grown in chemostats under ammonium or silicate limitation to examine its growth kinetics and changes in cellular chemical composition at different steady-state growth rates. When the relationship between the effluent limiting substrate concentration and steady-state growth rates was examined, deviations from the simple hyperbolic form of the Monod growth equation were noted at low and high dilution rates. The data from the plot of growth rate and substrate concentration were divided into 4 regions and the relationship of these region to cell quota is discussed. Two physiological states were identified. All populations grown at D〈0.05 h-1, regardless of the size of the cells or the magnitude of Q, exhibited a maximal growth rate of approximately 0.05 h-1, while populations grown at higher dilution rates (D〉0.06 h-1 to 0.14 h-1). The maximal value of growth rate is obtained only in cultures grown at very high dilution rates where nutrient shift-up appears to occur, the cell quota approaches a maximum and the heterogeneous cell population becomes more homogeneous.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00390939
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