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  • 1
    Electronic Resource
    Electronic Resource
    Hard X-ray images of the galactic centre (1987)
    [s.l.] : Nature Publishing Group
    Nature 330 (1987), S. 544-547 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The only detailed X-ray image of the galactic centre region until now was obtained by Watson et a/.1 in 1979 with the Einstein Observatory, using X-rays with energy 〈4.5 keV (ref. 1, referred to below as WWGH). Twelve point sources were seen in the ~1° field, together with diffuse emission ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/330544a0
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The distribution of iron in the Perseus cluster (1990)
    [s.l.] : Nature Publishing Group
    Nature 347 (1990), S. 450-452 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The coarse component of the dual X-ray telescope on Spacelab 2 (ref. 1) used coded-mask imaging2 to achieve angular resolution of 12' over a 6° field together with proportional-counter energy resolution covering the 2-32 keVband, recording ~7 x 105 photons from the Perseus cluster during an ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/347450a0
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    Paper (German National Licenses)
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  • 3
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    Differential effects of nitrate, ammonium, and urea as N sources for microbial communities in the North Pacific Ocean (2017)
    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 62 (6). pp. 2550-2574.
    Details
    Publication Date: 2021-04-23
    Description: Nitrogen (N) is the major limiting nutrient for phytoplankton growth and productivity in large parts of the world's oceans. Differential preferences for specific N substrates may be important in controlling phytoplankton community composition. To date, there is limited information on how specific N substrates influence the composition of naturally occurring microbial communities. We investigated the effect of nitrate ( math formula), ammonium ( math formula), and urea on microbial and phytoplankton community composition (cell abundances and 16S rRNA gene profiling) and functioning (photosynthetic activity, carbon fixation rates) in the oligotrophic waters of the North Pacific Ocean. All N substrates tested significantly stimulated phytoplankton growth and productivity. Urea resulted in the greatest (〉300%) increases in chlorophyll a (〈0.06 μg L−1 and ∼0.19 μg L−1 in the control and urea addition, respectively) and productivity (〈0.4 μmol C L−1 d−1 and ∼1.4 μmol C L−1 d−1 in the control and urea addition, respectively) at two experimental stations, largely due to increased abundances of Prochlorococcus (Cyanobacteria). Two abundant clades of Prochlorococcus, High Light I and II, demonstrated similar responses to urea, suggesting this substrate is likely an important N source for natural Prochlorococcus populations. In contrast, the heterotrophic community composition changed most in response to math formula. Finally, the time and magnitude of response to N amendments varied with geographic location, likely due to differences in microbial community composition and their nutrient status. Our results provide support for the hypothesis that changes in N supply would likely favor specific populations of phytoplankton in different oceanic regions and thus, affect both biogeochemical cycles and ecological processes.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1002/lno.10590
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Database of diazotrophs in global ocean: abundance, biomass and nitrogen fixation rates (2012)
    Copernicus Publications (EGU)
    In:  Earth System Science Data, 4 (1). pp. 47-73.
    Details
    Publication Date: 2020-05-13
    Description: Marine N2 fixing microorganisms, termed diazotrophs, are a key functional group in marine pelagic ecosystems. The biological fixation of dinitrogen (N2) to bioavailable nitrogen provides an important new source of nitrogen for pelagic marine ecosystems and influences primary productivity and organic matter export to the deep ocean. As one of a series of efforts to collect biomass and rates specific to different phytoplankton functional groups, we have constructed a database on diazotrophic organisms in the global pelagic upper ocean by compiling about 12 000 direct field measurements of cyanobacterial diazotroph abundances (based on microscopic cell counts or qPCR assays targeting the nifH genes) and N2 fixation rates. Biomass conversion factors are estimated based on cell sizes to convert abundance data to diazotrophic biomass. The database is limited spatially, lacking large regions of the ocean especially in the Indian Ocean. The data are approximately log-normal distributed, and large variances exist in most sub-databases with non-zero values differing 5 to 8 orders of magnitude. Reporting the geometric mean and the range of one geometric standard error below and above the geometric mean, the pelagic N2 fixation rate in the global ocean is estimated to be 62 (52–73) Tg N yr−1 and the pelagic diazotrophic biomass in the global ocean is estimated to be 2.1 (1.4–3.1) Tg C from cell counts and to 89 (43–150) Tg C from nifH-based abundances. Reporting the arithmetic mean and one standard error instead, these three global estimates are 140 ± 9.2 Tg N yr−1, 18 ± 1.8 Tg C and 590 ± 70 Tg C, respectively. Uncertainties related to biomass conversion factors can change the estimate of geometric mean pelagic diazotrophic biomass in the global ocean by about ±70%. It was recently established that the most commonly applied method used to measure N2 fixation has underestimated the true rates. As a result, one can expect that future rate measurements will shift the mean N2 fixation rate upward and may result in significantly higher estimates for the global N2 fixation. The evolving database can nevertheless be used to study spatial and temporal distributions and variations of marine N2 fixation, to validate geochemical estimates and to parameterize and validate biogeochemical models, keeping in mind that future rate measurements may rise in the future. The database is stored in PANGAEA (doi:10.1594/PANGAEA.774851).
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.5194/essd-4-47-2012
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Quantitative biogeography of picoprasinophytes establishes ecotype distributions and significant contributions to marine phytoplankton (2017)
    Wiley / Society for Applied Microbiology and Blackwell Publishing Ltd,
    In:  Environmental Microbiology, 19 (8). pp. 3219-3234.
    Details
    Publication Date: 2020-02-06
    Description: Bathycoccus and Ostreococcus are broadly distributed marine picoprasinophyte algae. We enumerated small phytoplankton using flow cytometry and qPCR assays for phylogenetically distinct Bathycoccus clades BI and BII and Ostreococcus clades OI and OII. Among 259 photic-zone samples from transects and time-series, Ostreococcus maxima occurred in the North Pacific coastal upwelling for OI (36 713 ± 1485 copies ml−1) and the Kuroshio Front for OII (50 189 ± 561 copies ml−1) and the two overlapped only in frontal regions. The Bathycoccus overlapped more often with maxima along Line-P for BI (10 667 ± 1299 copies ml−1) and the tropical Atlantic for BII (4125 ± 339 copies ml−1). Only BII and OII were detected at warm oligotrophic sites, accounting for 34 ± 13 of 1589 ± 448 eukaryotic phytoplankton cells ml−1 (annual average) at Station ALOHA's deep chlorophyll maximum. Significant distributional and molecular differences lead us to propose that Bathycoccus clade BII represents a separate species which tolerates higher temperature oceanic conditions than Bathycoccus prasinos (BI). Morphological differences were not evident, but quick-freeze deep-etch electron microscopy provided insight into Bathycoccus scale formation. Our results highlight the importance of quantitative seasonal abundance data for inferring ecological distributions and demonstrate significant, differential picoprasinophyte contributions in mesotrophic and open-ocean waters. © 2017 The Authors. Environmental Microbiology published by Society for Applied Microbiology and John Wiley & Sons Ltd.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1111/1462-2920.13812
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    The nature of the island and banana states in atoll sources and a unified model for low-mass X-ray binaries (2014)
    Oxford University Press
    Details
    Publication Date: 2014-02-20
    Description: We propose an explanation of the island and banana states and the relation between atoll and Z-track sources, constituting a unified model for low-mass X-ray binaries (LMXB). We find a dramatic transition at a luminosity of 1–2 10 37 erg s –1 above which the high-energy cut-off E CO of the Comptonized emission in all sources is low at a few keV. There is thermal equilibrium between the neutron star at ~2 keV and the Comptonizing accretion disc corona (ADC) causing the low E CO in the banana state of atolls and all states of the Z-track sources. Below this luminosity, E CO increases towards 100 keV causing the hardness of the island state. Thermal equilibrium is lost, the ADC becoming much hotter than the neutron star via an additional coronal heating mechanism. This suggests a unified model of LMXB: the banana state is a basic state with the mass accretion rate $\dot{M}$ increasing, corresponding to the normal branch of Z-track sources. The island state has high ADC temperature, this state not existing in the Z-sources with luminosities much greater than the critical value. The Z-track sources have an additional flaring branch consistent with unstable nuclear burning on the neutron star at high $\dot{M}$ . This burning regime does not exist at low $\dot{M}$ so this branch is not seen in atolls (except GX atolls). The horizontal branch in Z-track sources has a strong increase in radiation pressure disrupting the inner disc and launching relativistic jets.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Planktonic Euryarchaeota produce tetraether lipids [Environmental Sciences] (2014)
    National Academy of Sciences
    Details
    Publication Date: 2014-07-09
    Description: Archaea are ubiquitous in marine plankton, and fossil forms of archaeal tetraether membrane lipids in sedimentary rocks document their participation in marine biogeochemical cycles for 〉100 million years. Ribosomal RNA surveys have identified four major clades of planktonic archaea but, to date, tetraether lipids have been characterized in only one,...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 8
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    Predictable and efficient carbon sequestration in the North Pacific Ocean supported by symbiotic nitrogen fixation [Ecology] (2012)
    National Academy of Sciences
    Details
    Publication Date: 2012-02-08
    Description: The atmospheric and deep sea reservoirs of carbon dioxide are linked via physical, chemical, and biological processes. The last of these include photosynthesis, particle settling, and organic matter remineralization, and are collectively termed the “biological carbon pump.” Herein, we present results from a 13-y (1992–2004) sediment trap experiment conducted in the permanently oligotrophic North Pacific Subtropical Gyre that document a large, rapid, and predictable summertime (July 15–August 15) pulse in particulate matter export to the deep sea (4,000 m). Peak daily fluxes of particulate matter during the summer export pulse (SEP) average 408, 283, 24.1, 1.1, and 67.5 μmol·m−2·d−1 for total carbon, organic carbon, nitrogen, phosphorus (PP), and biogenic silica, respectively. The SEP is approximately threefold greater than mean wintertime particle fluxes and fuels more efficient carbon sequestration because of low remineralization during downward transit that leads to elevated total carbon/PP and organic carbon/PP particle stoichiometry (371:1 and 250:1, respectively). Our long-term observations suggest that seasonal changes in the microbial assemblage, namely, summertime increases in the biomass and productivity of symbiotic nitrogen-fixing cyanobacteria in association with diatoms, are the main cause of the prominent SEP. The recurrent SEP is enigmatic because it is focused in time despite the absence of any obvious predictable stimulus or habitat condition. We hypothesize that changes in day length (photoperiodism) may be an important environmental cue to initiate aggregation and subsequent export of organic matter to the deep sea.
    Keywords: Inaugural Articles
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 9
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    Comparative Assessment of Nitrogen Fixation Methodologies, Conducted in the Oligotrophic North Pacific Ocean [Methods] (2012)
    The American Society for Microbiology (ASM)
    Details
    Publication Date: 2012-08-25
    Description: Resolution of the nitrogen (N) cycle in the marine environment requires an accurate assessment of dinitrogen (N 2 ) fixation. We present here an update on progress in conducting field measurements of acetylene reduction (AR) and 15 N 2 tracer assimilation in the oligotrophic North Pacific Subtropical Gyre (NPSG). The AR assay was conducted on discrete seawater samples using a headspace analysis system, followed by quantification of ethylene (C 2 H 4 ) with a reducing compound photodetector. The rates of C 2 H 4 production were measurable for nonconcentrated seawater samples after an incubation period of 3 to 4 h. The 15 N 2 tracer measurements compared the addition of 15 N 2 as a gas bubble and dissolved as 15 N 2 enriched seawater. On all sampling occasions and at all depths, a 2- to 6-fold increase in the rate of 15 N 2 assimilation was measured when 15 N 2 -enriched seawater was added to the seawater sample compared to the addition of 15 N 2 as a gas bubble. In addition, we show that the 15 N 2 -enriched seawater can be prepared prior to its use with no detectable loss (〈1.7%) of dissolved 15 N 2 during 4 weeks of storage, facilitating its use in the field. The ratio of C 2 H 4 production to 15 N 2 assimilation varied from 7 to 27 when measured simultaneously in surface seawater samples. Collectively, the modifications to the AR assay and the 15 N 2 assimilation technique present opportunities for more accurate and high frequency measurements (e.g., diel scale) of N 2 fixation, providing further insight into the contribution of different groups of diazotrophs to the input of N in the global oceans.
    Print ISSN: 0099-2240
    Electronic ISSN: 1098-5336
    Topics: Biology
    Published by The American Society for Microbiology (ASM)
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  • 10
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    Relationship between Abundance and Specific Activity of Bacterioplankton in Open Ocean Surface Waters [Microbial Ecology] (2012)
    The American Society for Microbiology (ASM)
    Details
    Publication Date: 2012-12-20
    Description: Marine microbial communities are complex and dynamic, and their ecology impacts biogeochemical cycles in pelagic ecosystems. Yet, little is known about the relative activities of different microbial populations within genetically diverse communities. We used rRNA as a proxy for activity to quantify the relative specific activities (rRNA/ribosomal DNA [rDNA or rRNA genes]) of the eubacterial populations and to identify locations or clades for which there are uncouplings between specific activity and abundance. After analyzing 1.6 million sequences from 16S rDNA and rRNA (cDNA) libraries from two euphotic depths from a representative site in the Pacific Ocean, we show that although there is an overall positive relationship between the abundances (rDNAs) and activities (rRNAs) among populations of the bacterial community, for some populations these measures are uncoupled. Different ecological strategies are exemplified by the two numerically dominant clades at this site: the cyanobacterium Prochlorococcus is abundant but disproportionately more active, while the heterotrophic SAR11 is abundant but less active. Other rare populations, such as Alteromonas , have high specific activities in spite of their low abundances, suggesting intense population regulation. More detailed analyses using a complementary quantitative PCR (qPCR)-based approach of measuring relative specific activity for Prochlorococcus populations in the Pacific and Atlantic Oceans also show that specific activity, but not abundance, reflects the key drivers of light and nutrients in this system; our results also suggest substantial top-down regulation (e.g., grazing, viruses, or organismal interactions) or transport (e.g., mixing, immigration, or emigration) of these populations. Thus, we show here that abundance and specific activity can be uncoupled in open ocean systems and that describing both is critical to characterizing microbial communities and predicting marine ecosystem functioning and responses to change.
    Print ISSN: 0099-2240
    Electronic ISSN: 1098-5336
    Topics: Biology
    Published by The American Society for Microbiology (ASM)
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