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  • 1
    Publication Date: 2017-01-04
    Description: Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 26 (2012): GB2005, doi:10.1029/2010GB004028.
    Description: In connection with the Palmer LTER program, mixed layer water samples were collected during the cruise of the L.M. Gould in Jan., 2008 at 49 stations on a 20 × 100 km grid in the West Antarctica Peninsula (WAP) region of the Southern Ocean. In this study, [O2]/[Ar] ratios and the triple isotope composition of dissolved O2 were measured, and were used to estimate net community O2 production (NCP) and gross primary O2 production (GPP), respectively. These estimates are further converted to carbon export production, primary production and the f-ratio. Our measurements give NCP ranging from −3 to 76 mmol O2 m−2 day−1 (−25 to 650 mg C m−2 day−1), and GPP from 40 to 220 mmol O2 m−2 day−1 (180 to 1010 mg C m−2 day−1). The O2 NCP/GPP ratios range from −0.04 to 0.43, corresponding to f-ratios of −0.08 to 0.83. NCP and the NCP/GPP ratio are highest in the northern coastal areas, and decrease to lower values toward the southern coastal area and the open ocean. The inshore-offshore gradient appears to be regulated primarily by iron availability, as supported by the positive correlation between NCP and Fv/Fm ratios (r2 = 0.22, p 〈 0.05). Mixed layer depth (MLD) is inversely correlated with NCP (r2 = 0.21, p 〈 0.002) and NCP/GPP (r2 = 0.21, p 〈 0.02), and highest NCP occurred in the fresh water lenses probably formed from melted coastal glaciers. These results suggest that export production and the f-ratio increase where water stratification is intensified by input of fresh meltwater, and that mixed layer stratification is the major factor regulating NCP in the inner-shelf and coastal regions. Along-shelf variability of phytoplankton community composition is highly correlated with NCP, i.e., NCP increases when the diatom-dominated community in the south transitions to the cryptophyte-dominated one in the north. A high correlation is also observed between NCP and the logarithm of the surface chlorophyll concentration (r2 = 0.72, p 〈 0.0001) , which makes it possible to estimate carbon export as a function of Chl a concentration in this region.
    Description: This research was supported by NSF-OPP grant 0823101 to Ducklow and NASA Earth and Space Sciences Fellowship to Huang.
    Description: 2012-10-24
    Keywords: Southern Ocean ; Chlorophyll ; Gross primary production ; Net community production ; Oxygen isotopes ; Phytoplankton
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
    Publication Date: 2017-01-05
    Description: Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 23 (2009): GB1006, doi:10.1029/2007GB003162.
    Description: The isotopic composition of dissolved oxygen in the mesopelagic ocean is a unique tracer of respiration and transport. New δ 18O of O2 data from the tropical South Atlantic oxygen minimum zone are presented and compared to global δ 18O data. The δ 18O variability in oxygen poor waters is attributed to differences in physical and biogeochemical processes. Simple respiration-transport models show that both isopycnal diffusion and advection must be properly considered when interpreting oxygen isotope signatures along an isopycnal surface. We estimate rates of respiration and oxygen isotope fractionation for the study region using a two-dimensional (2-D) isopycnal and 1-D diapycnal model. Estimated respiration rates are consistent with previous studies. However, to account for observed δ 18O values at low [O2], model solutions need to invoke either very low [O2] that have not been observed in the South Atlantic or an isotope effect that is lower than values measured in the laboratory or euphotic zone.
    Description: We gratefully acknowledge financial support from NSF and NASA.
    Keywords: Oxygen isotope ; Respiration ; Chemical tracer
    Repository Name: Woods Hole Open Access Server
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  • 3
    Publication Date: 2017-01-05
    Description: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 118 (2013): 385–399, doi:10.1002/jgrg.20032.
    Description: The sea-air biological O2 flux assessed from measurements of surface O2 supersaturation in excess of Ar supersaturation (“O2 bioflux”) is increasingly being used to constrain net community production (NCP) in the upper ocean mixed layer. In making these calculations, one generally assumes that NCP is at steady state, mixed layer depth is constant, and there is no O2 exchange across the base of the mixed layer. The object of this paper is to evaluate the magnitude of errors introduced by violations of these assumptions. Therefore, we examine the differences between the sea-air biological O2 flux and NCP in the Southern Ocean mixed layer as calculated using two ocean biogeochemistry general circulation models. In this approach, NCP is considered a known entity in the prognostic model, whereas O2 bioflux is estimated using the model-predicted O2/Ar ratio to compute the mixed layer biological O2 saturation and the gas transfer velocity to calculate flux. We find that the simulated biological O2 flux gives an accurate picture of the regional-scale patterns and trends in model NCP. However, on local scales, violations of the assumptions behind the O2/Ar method lead to significant, non-uniform differences between model NCP and biological O2 flux. These errors arise from two main sources. First, venting of biological O2 to the atmosphere can be misaligned from NCP in both time and space. Second, vertical fluxes of oxygen across the base of the mixed layer complicate the relationship between NCP and the biological O2 flux. Our calculations show that low values of O2 bioflux correctly register that NCP is also low (〈10 mmol m−2 day−1), but fractional errors are large when rates are this low. Values between 10 and 40 mmol m−2 day−1 in areas with intermediate mixed layer depths of 30 to 50 m have the smallest absolute and relative errors. Areas with O2 bioflux higher than 30 mmol m−2 day−1 and mixed layers deeper than 40 m tend to underestimate NCP by up to 20 mmol m−2 day−1. Excluding time periods when mixed layer biological O2 is undersaturated, O2 bioflux underestimates time-averaged NCP by 5%–15%. If these time periods are included, O2 bioflux underestimates mixed layer NCP by 20%–35% in the Southern Ocean. The higher error estimate is relevant if one wants to estimate seasonal NCP since a significant amount of biological production takes place when mixed layer biological O2 is undersaturated.
    Description: This work was supported in part by funding from the National Aeronautic and Space Administration (NASA NNX08AF12G) and National Science Foundation (NSF OPP-0823101).
    Keywords: Biological production ; Southern Ocean ; O2/Ar ; Modeling ; Oxygen ; GCM
    Repository Name: Woods Hole Open Access Server
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  • 4
    Publication Date: 2017-01-05
    Description: Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 24 (2010): GB4001, doi:10.1029/2009GB003651.
    Description: Net community production (NCP) and gross primary production (GPP) are two key metrics for quantifying the biological carbon cycle. In this study, we present a detailed characterization of NCP and GPP in the western equatorial Pacific during August and September 2006. We use continuous measurements of dissolved gases (O2 and Ar) in the surface water in order to quantify NCP at subkilometer scale resolution. We constrain GPP in discrete samples using the triple isotopic composition of O2. We find the average NCP in the western equatorial Pacific is 5.9 ± 0.9 mmol O2 m−2 d−1 (equivalent to 1.5 ± 0.2 mol C m−2 yr−1 with error estimates reflecting 1σ confidence levels) and the average GPP is 121 ± 34 mmol O2 m−2 d−1 (equivalent to 32 ± 9 mol C m−2 yr−1). The measurements reveal significant spatial variability on length scales as small as 50 km. The NCP/GPP ratio is 5.7% ± 1.8%. We also present results for NCP and GPP in the coastal area off Papua New Guinea and for GPP in the central Pacific along the equator.
    Description: This work was supported by the NSF Chemical Oceanography and the Office of Polar Programs, by the NOAA climate and global change program (fellowship to RHRS), and by Princeton University (Hess fellowship to RHRS).
    Keywords: Production ; Triple oxygen isotopes ; Equatorial pacific
    Repository Name: Woods Hole Open Access Server
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  • 5
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    Bonn: Stiftung Entwicklung und Frieden (SEF)
    Publication Date: 2018-03-01
    Description: Am 10./11. Oktober 2013 treffen sich im japanischen Minamata Regierungsvertreter aus aller Welt zur Zeichnung eines neuen Umweltabkommens. In den 1950 Jahren war Minamata Schauplatz einer massenhaften Quecksilbervergiftung durch ungereinigtes Abwasser eines Chemiewerks geworden. Die seit 2009 im Rahmen des UN-Umweltprogramms UNEP ausgehandelte Quecksilber-Konvention hat nun zum Ziel, die menschliche Gesundheit und die Umwelt vor anthropogenen Quecksilber-Emissionen zu schützen. Im Global Governance Spotlight 7 013 beschreiben Elena Lymberidi-Settimo und Michael T. Bender die Entstehungsgeschichte sowie die Stärken und Schwächen dieses neuen Abkommens. Sie enden mit einem Appell an alle Staaten, die Konvention schnell zu ratifizieren und die Zeit bis zu ihrem Inkrafttreten für vielfältige Maßnahmen zum Schutz vor Quecksilberemissionen zu nutzen.
    Keywords: ddc:320
    Repository Name: EconStor: OA server of the German National Library of Economics - Leibniz Information Centre for Economics
    Language: German
    Type: doc-type:report
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 269 (1977), S. 793-794 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Young M. edulis (7-15 mm long) were collected from Nar-ragansett Bay, Rhode Island and cultured for 8 weeks in aerated 4.5-1 glass aquaria. The water was changed at weekly intervals and the mussels were fed a suspension of Isochrysis. Twenty mussels were placed in each tank. The culture solutions ...
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 2019-08-05
    Description: A numerical algorithm based on Fermat's Principle was developed to simulate the propagation of Global Positioning System (GPS) radio signals in the refractivity field of a numerical weather model. The unique in the proposed algorithm is that the ray-trajectory automatically involves the location of the ground-based receiver and the satellite, i.e. the posed two-point boundary value problem is solved by an implicit finite difference scheme. This feature of the algorithm allows the fast and accurate computation of the signal travel-time delay, referred to as Slant Total Delay (STD), between a satellite and a ground-based receiver. We provide a technical description of the algorithm and estimate the uncertainty of STDs due to simplifying assumptions in the algorithm and due to the uncertainty of the refractivity field. In a first application, we compare STDs retrieved from GPS phase-observations at the German Research Centre for Geosciences Potsdam (GFZ STDs) with STDs derived from the European Center for Medium-Range Weather Forecasts analyses (ECMWF STDs). The statistical comparison for one month (August 2007) for a large and continuously operating network of ground-based receivers in Germany indicates good agreement between GFZ STDs and ECMWF STDs; the standard deviation is 0.5% and the mean deviation is 0.1%.
    Type: Article , PeerReviewed
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  • 8
    Publication Date: 2014-12-09
    Description: Water vapor plays an important role in meteorological applications; GeoForschungsZentrum (GFZ) therefore developed a tomographic system to derive 3-D distributions of the tropospheric water vapor above Germany using GPS data from about 300 ground stations. Input data for the tomographic reconstructions are generated by the Earth Parameter and Orbit determination System (EPOS) software of the GFZ, which provides zenith total delay (ZTD), integrated water vapor (IWV) and slant total delay (STD) data operationally with a temporal resolution of 2.5 min (STD) and 15 min (ZTD, IWV). The water vapor distribution in the atmosphere is derived by tomographic reconstruction techniques. The quality of the solution is dependent on many factors such as the spatial coverage of the atmosphere with slant paths, the spatial distribution of their intersections and the accuracy of the input observations. Independent observations are required to validate the tomographic reconstructions and to get precise information on the accuracy of the derived 3-D water vapor fields. To determine the quality of the GPS tomography, more than 8000 vertical water vapor profiles at 13 German radiosonde stations were used for the comparison. The radiosondes were launched twice a day (at 00:00 UTC and 12:00 UTC) in 2007. In this paper, parameters of the entire profiles such as the wet refractivity, and the zenith wet delay have been compared. Before the validation the temporal and spatial distribution of the slant paths, serving as a basis for tomographic reconstruction, as well as their angular distribution were studied. The mean wet refractivity differences between tomography and radiosonde data for all points vary from −1.3 to 0.3, and the root mean square is within the range of 6.5–9. About 32% of 6803 profiles match well, 23% match badly and 45% are difficult to classify as they match only in parts.
    Type: Article , PeerReviewed
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  • 9
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    AGU (American Geological Union)
    In:  Global Biogeochemical Cycles, 7 (3). pp. 679-694.
    Publication Date: 2017-11-03
    Description: We measured the respiratory isotope effect ϵresp for seven representative unicellular marine organisms. The bacterium Pseudomonas halodurans, the diatom Phaeodactylum tricornutum, the phytoflagellates Cryptomonas baltica and Dunaliella tertiolecta, the heterotrophic flagellates Paraphysomonas imperforata and Bodo sp., and the ciliate Uronema sp. exhibit ϵresp values in the range 14-26‰. We also measured ϵresp for three metazoans. The ϵresp for the copepod Acartia tonsa ranged from 17 to 25‰, while two larger organisms, the mollusk Mercenaria mercenaria and the salmon Salmo salmar, respire with a smaller ϵresp of 5-10‰. The average respiratory isotope effect of the dominant marine respirers (the bacteria, microalgae and zooplankton) is about 20 ± 3‰. An ϵresp of this magnitude supports the hypothesis that the photosynthesis-respiration cycle is responsible for the 23.5‰ enrichment in the δ18O ratio of atmospheric O2 relative to seawater (the Dole effect). The large value and high variability in the average ϵresp limits the usefulness of a proposed method using the δ18O of naturally fractionated dissolved O2 in seawater as a tracer of primary production in the oligotrophic ocean.
    Type: Article , PeerReviewed
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  • 10
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    AGU (American Geological Union)
    In:  Global Biogeochemical Cycles, 8 (3). pp. 363-376.
    Publication Date: 2017-11-03
    Description: We review the current understanding of the Dole effect (the observed difference between the δ18O of atmospheric O2 and that of seawater) and its causes, extend the record of variations in the Dole effect back to 130 kyr before present using data on the δ18O of O2 obtained from studying the Vostok ice core (Sowers et al., 1993), and discuss the significance of temporal variations. The Dole effect reflects oxygen isotope fractionation during photosynthesis, respiration, and hydrologic processes (evaporation, precipitation, and evapotranspiration). Our best prediction of the present-day Dole effect, +20.8‰, is considerably lower than the observed value, +23.5‰, and we discuss possible causes of this discrepancy. During the past 130 kyr, the Dole effect has been 0.05‰ lower than the present value, on average. The standard deviation of the Dole effect from the mean has been only ±0.2‰, and the Dole effect is nearly unchanged between glacial maxima and interglacial periods. The small variability in the Dole effect suggests that relative rates of primary production in the land and marine realms have been relatively constant. Most periodic variability in the Dole effect is in the precession band, suggesting that changes in this global biogeochemical term reflects variations in low-latitude land hydrology and productivity or possibly variability in low-latitude oceanic productivity.
    Type: Article , PeerReviewed
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