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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 354 (1991), S. 293-296 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A transect was followed from close to the Equator to the Gulf of Oman during September and October 1986, and dissolved methane was measured in the atmosphere, and from the sea surface to the bottom at 13 stations. Figure 1 shows that methane concentrations varied considerably with depth, being ...
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 357 (1992), S. 397-399 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Data on the wet deposition of nitrate and ammonium are available for Bermuda (North Atlantic)7, and for Amsterdam Island (South Indian Ocean)8 for a nine-year period. The data were obtained using methods described previously7'8. The record (Table 1) shows that the median and ...
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 346 (1990), S. 826-828 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A transect of the northwest Indian Ocean (Fig. 1) was followed from close to the Equator (00°04' N 65°05' E), across the Arabian Sea into the Gulf of Oman (24°49' N 57°13' E) during September-October 1986. Vertical profiles of dissolved N2O (and other oceanographic variables) were ...
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  • 4
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stable isotope tracer methods are gaining popularity in many fields, including environmental science, agriculture and medicine. This is particularly true in the clinical sciences, where the use of radioisotopes can be precluded on ethical grounds and 13C and 15N tracers are being used more frequently for metabolic studies. Mass spectrometry is the preferred technique for isotope analysis. Sample preparation techniques for classical isotope ratio mass spectrometry are often tedious and can involve the use of complex vacuum apparatus that is quite foreign to the biological chemist. Organic gas chromatography/mass spectrometry (GC/MS) overcomes many sample preparation problems but may lack the performance needed for isotope analysis. This paper describes the analysis of 13C using an automatic elemental gas chromatograph interfaced to an isotope ratio mass spectrometer, a system which was developed initially for the analysis of 15N.Details of the residual gas background, peak broadening due to high carrier gas pressures, mass spectral linearity and response to changing sample peak heights and variations of the measured isotope ratio with sample pressure are described. Sensitivity and performance data (reproducibility ± 0.62% at natural abundance) are also given. The potential of this system for other gas chromatographic applications, automatic data handling and the possible simultaneous analysis of 13C and 15N are also discussed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-515X
    Keywords: continental shelf ; estuaries ; mass balance ; nitrogen ; North Atlantic ; nutrient budget ; phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Five large rivers that discharge on the western North Atlantic continental shelf carry about 45% of the nitrogen (N) and 70% of the phosphorus (P) that others estimate to be the total flux of these elements from the entire North Atlantic watershed, including North, Central and South America, Europe, and Northwest Africa. We estimate that 61 · 109 moles y−1 of N and 20 · 109 moles y−1 of P from the large rivers are buried with sediments in their deltas, and that an equal amount of N and P from the large rivers is lost to the shelf through burial of river sediments that are deposited directly on the continental slope. The effective transport of active N and P from land to the shelf through the very large rivers is thus reduced to 292 · 109 moles y−1 of N and 13 · 109 moles y−1 of P. The remaining riverine fluxes from land must pass through estuaries. An analysis of annual total N and total P budgets for various estuaries around the North Atlantic revealed that the net fractional transport of these nutrients through estuaries to the continental shelf is inversely correlated with the log mean residence time of water in the system. This is consistent with numerous observations of nutrient retention and loss in temperate lakes. Denitrification is the major process responsible for removing N in most estuaries, and the fraction of total N input that is denitrified appears to be directly proportional to the log mean water residence time. In general, we estimate that estuarine processes retain and remove 30–65% of the total N and 10–55% of the total P that would otherwise pass into the coastal ocean. The resulting transport through estuaries to the shelf amounts to 172–335 · 109 moles y−1 of N and 11–19 · 109 moles y−1 of P. These values are similar to the effective contribution from the large rivers that discharge directly on the shelf. For the North Atlantic shelf as a whole, N fluxes from major rivers and estuaries exceed atmospheric deposition by a factor of 3.5–4.7, but this varies widely among regions of the shelf. For example, on the U.S. Atlantic shelf and on the northwest European shelf, atmospheric deposition of N may exceed estuarine exports. Denitrification in shelf sediments exceeds the combined N input from land and atmosphere by a factor of 1.4–2.2. This deficit must be met by a flux of N from the deeper ocean. Burial of organic matter fixed on the shelf removes only a small fraction of the total N and P input (2–12% of N from land and atmosphere; 1–17% of P), but it may be a significant loss for P in the North Sea and some other regions. The removal of N and P in fisheries landings is very small. The gross exchange of N and P between the shelf and the open ocean is much larger than inputs from land and, for the North Atlantic shelf as a whole, it may be much larger than the N and P removed through denitrification, burial, and fisheries. Overall, the North Atlantic continental shelf appears to remove some 700–950· 109 moles of N each year from the deep ocean and to transport somewhere between 18 and 30 · 109 moles of P to the open sea. If the N and P associated with riverine sediments deposited on the continental slope are included in the total balance, the net flux of N to the shelf is reduced by 60 · 109 moles y−1 and the P flux to the ocean is increased by 20 · 109 moles y−1. These conclusions are quite tentative, however, because of large uncertainties in our estimates of some important terms in the shelf mass balance.
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  • 6
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Microzooplankton grazing activity in the Celtic Sea and Carmarthen Bay in summer 1983 and autumn 1984 was investigated by applying a dilution technique to high-performance liquid chromatographic (HPLC) analysis of photosynthetic pigments in phytoplankton present within natural microplankton communities. Specific grazing rates on phytoplankton, as measured by the utilisation of chlorophyll a, were high and varied seasonally. In surface waters during the autumn, grazing varied between 0.4 d-1 in the bay and 1.0 d-1 in the Celtic Sea, indicating that 30 and 65% of the algal standing stocks, respectively, were grazed daily. Grazing rates by microzooplankton within the thermocline in summer suggest that 13 to 42% of the crop was grazed each day. Microzooplankton showed selection for algae containing chlorophyll b, in spite of a predominance of chlorophyll c within the phytoplankton community. Changes in taxon-specific carotenoids indicated strong selection for peridinin, lutein and alloxanthin and selection against fucoxanthin and diadinoxanthin. This indicates a trophic preference by microzooplankton for dinoflagellates, cryptophytes, chlorophytes and prasinophytes and selection against diatoms, even when the latter group forms the largest crop within the phytoplankton. Interestingly, those algal taxa preferentially grazed also showed the highest specific growth-rates, suggesting a dynamic feed-back between microzooplankton and phytoplankton. Conversion of grazing rates on each pigment into chlorophyll a equivalents suggests firstly, that in only one experiment could all the grazed chlorophyll a be accounted for by the attrition of other chlorophylls and carotenoids, and secondly that in spite of negative selection, a greater mass of diatoms could be grazed by microzooplankton than any other algal taxon. The former may be due either to a fundamental difference in the break-down rates of chlorophyll a compared to other pigments, or to cyanobacteria forming a significant food source for microzooplankton. In either case, chlorophyll a is considered to be a good measure of grazing activity by microzooplankton.
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  • 7
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The results from a series of five cruises (August 1979–January 1981) to examine rates of primary production, nitrogen assimilation and regeneration in Carmarthen Bay, S. Wales, are presented. Chlorophyll, primary production and regeneration were distributed irregularly throughout the bay, with the highest concentrations and rates being found around the shallow periphery. Nitrate was the dominant form of nitrogen assimilated by the phytoplankton, apart from periods of high biomass during the summer when ammonium assumed a more important role. The rates of ammonium regeneration from microheterotrophs were greater than the ammonium demand over much of the year, indicating that the bay was a net exporter of ammonium and was a physically dominated “open” system. During the summer, the rates of ammonium regeneration and assimilation were similar, indicating efficient recycling of nutrients.
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  • 8
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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