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  • 1
    Electronic Resource
    Electronic Resource
    Increased marine production of N 2 O due to intensifying anoxia on the Indian continental shelf (2000)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 408 (2000), S. 346-349 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Eutrophication of surface waters and hypoxia in bottom waters has been increasing in many coastal areas, leading to very large depletions of marine life in the affected regions. These areas of high surface productivity and low bottom-water oxygen concentration are caused by increasing ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35042551
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    A comparative study of Pleistocene phosphorites from the continental slope off western India (2000)
    Oxford UK : Blackwell Science Ltd
    Sedimentology 47 (2000), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Two types of phosphorite recovered from the continental slope off western India are described. The first type, phosphorite 1, comprises a hard, grey nodule composed of carbonate fluorapatite (CFA) and calcite as major minerals. The phosphorite consists of light-brown microcrystalline apatite containing a few skeletal fragments and planktonic foraminifera. Scanning electron microscope (SEM) studies show evidence of dissolution of skeletal calcite and filling of the resulting cavities by phosphate composed of ovoid to rod-shaped apatite microparticles. Apatite also occurs as coatings on these particles. The P2O5 content of the phosphorite is 29%, and the CO2 content of the CFA is about 4·5%. The rare-earth element (REE) abundance (ΣREE=2·02 μg g–1) is lower than in other modern phosphorites. The 87Sr/86Sr ratio and ɛNd value of this sample are 0·70921 and –9·9 respectively. The 14C age found through accelerator mass spectrometry (AMS) dating (18 720 ± 120 years BP) is much younger than that determined by the U-series method (100 ka). The second type, phosphorite 2, comprises a friable, light-brown nodule consisting of CFA as the only major mineral, with a CO2 content of the CFA of 4·5%. In thin section, the phosphate is light brown and homogeneous, and a few bone fragments are present. The P2O5 content is 33%, and REE contents (ΣREE = 0·18 μg g–1) are lower than in phosphorite 1. The age of phosphorite 2 is 〉300 ka. Phosphorite 1 appears to have formed during the late Pleistocene through replacement of carbonate by phosphate; phosphorite 2 is also of Pleistocene age but is much older than phosphorite 1. The initial substrate for phosphorite 2 was a fish coprolite, which was subsequently phosphatized during slow sedimentation under low-energy conditions. Microbial mediation is evident in both phosphorites. The colour, density and P2O5 content of the phosphorites are found to be dependent on the nature of the initial substrates and physico-chemical conditions during phosphatization. The CO2 content of the CFA is not related to the precursor carbonate phase. The nature of sediments, rates of sedimentation and the time spent undergoing phosphogenesis at the sediment–water interface may control REE concentrations in phosphorites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3091.2000.00331.x
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  • 3
    Electronic Resource
    Electronic Resource
    N 2 0 production in the ocean (1991)
    [s.l.] : Nature Publishing Group
    Nature 349 (1991), S. 373-374 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR-Recent measurements of the 15N:14N ratio (〈515N) of dissolved nitrous oxide (N2O) in sea water have revived the controversy concerning the mechanisms of N2O production in the ocean. The observed high (515N of N2O has been interpreted differently by Yoshida et ai' and by Kim and Craig2 to ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/349373b0
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  • 4
    Electronic Resource
    Electronic Resource
    Budgetary and biogeochemical implications of N 2 O isotope signatures in the Arabian Sea (1998)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 394 (1998), S. 462-464 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Nitrous oxide (N2O) is an important greenhouse gas that also plays a role in the chemistry of stratospheric ozone depletion, but its atmospheric budget has yet to be well-quantified. However, multi-isotope characterization of N2O emitted from various natural sources is a ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/28828
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  • 5
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    The next generation of iron fertilization experiments in the Southern Ocean. (2008)
    In:  EPIC3Philosophical Transactions of the Royal Society A, 366(1882), pp. 3947-3967
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
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    Ocean iron fertilization - Moving forward in a sea of uncertainty. (2008)
    In:  EPIC3Science, 319(5860), 162 p.
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 7
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    The Arabian Sea as a high-nutrient, low-chlorophyll region during the late Southwest Monsoon (2010)
    Copernicus Publications on behalf of the European Geosciences Union
    Details
    Publication Date: 2022-05-25
    Description: © The Authors, 2010. This article is distributed under the terms of the Creative Commons Attribution 3.0 License. The definitive version was published in Biogeosciences 7 (2010): 2091-2100, doi:10.5194/bg-7-2091-2010.
    Description: Extensive observations were made during the late Southwest Monsoon of 2004 over the Indian and Omani shelves, and along a transect that extended from the southern coast of Oman to the central west coast of India, tracking the southern leg of the US JGOFS expedition (1994–1995) in the west. The data are used, in conjunction with satellite-derived data, to investigate long-term trends in chlorophyll and sea surface temperature, indicators of upwelling intensity, and to understand factors that control primary production (PP) in the Arabian Sea, focussing on the role of iron. Our results do not support an intensification of upwelling in the western Arabian Sea, reported to have been caused by the decline in the winter/spring Eurasian snow cover since 1997. We also noticed, for the first time, an unexpected development of high-nutrient, low-chlorophyll condition off the southern Omani coast. This feature, coupled with other characteristics of the system, such as a narrow shelf and relatively low iron concentrations in surface waters, suggest a close similarity between the Omani upwelling system and the Peruvian and California upwelling systems, where PP is limited by iron. Iron limitation of PP may complicate simple relationship between upwelling and PP assumed by previous workers, and contribute to the anomalous offshore occurrence of the most severe oxygen (O2) depletion in the region. Over the much wider Indian shelf, which experiences large-scale bottom water O2-depletion in summer, adequate iron supply from reducing bottom-waters and sediments seems to support moderately high PP; however, such production is restricted to the thin, oxygenated surface layer, probably because of the unsuitability of the O2-depleted environment for the growth of oxygenic photosynthesizers.
    Description: Financial support was provided by CSIR through the Network Project CMM0009 to SWAN and by NSF through OCE-0327227S to JWM.
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 8
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    Seasonal occurrence of anoxygenic photosynthesis in Tillari and Selaulim reservoirs, Western India (2012)
    Copernicus Publications on behalf of the European Geosciences Union
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biogeosciences 9 (2012): 2485-2495, doi:10.5194/bg-9-2485-2012.
    Description: Phytoplankton and bacterial pigment compositions were determined by high performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS) in two freshwater reservoirs (Tillari Dam and Selaulim Dam), which are located at the foothills of the Western Ghats in India. These reservoirs experience anoxia in the hypolimnion during summer. Water samples were collected from both reservoirs during anoxic periods while one of them (Tillari Reservoir) was also sampled in winter, when convective mixing results in well-oxygenated conditions throughout the water column. During the period of anoxia (summer), bacteriochlorophyll (BChl) e isomers and isorenieratene, characteristic of brown sulfur bacteria, were dominant in the anoxic (sulfidic) layer of the Tillari Reservoir under low light intensities. The winter observations showed the dominance of small cells of Chlorophyll b-containing green algae and cyanobacteria, with minor presence of fucoxanthin-containing diatoms and peridinin-containing dinoflagellates. Using total BChl e concentration observed in June, the standing stock of brown sulfur bacteria carbon in the anoxic compartment of Tillari Reservoir was estimated to be 2.27 gC m−2, which is much higher than the similar estimate for carbon derived from oxygenic photosynthesis (0.82 gC m−2. The Selaulim Reservoir also displayed similar characteristics with the presence of BChl e isomers and isorenieratene in the anoxic hypolimnion during summer. Although sulfidic conditions prevailed in the water column below the thermocline, the occurrence of photo-autotrophic bacteria was restricted only to mid-depths (maximal concentration of BChl e isomers was detected at 0.2% of the surface incident light). This shows that the vertical distribution of photo-autotrophic sulfur bacteria is primarily controlled by light penetration in the water column where the presence of H2S provides a suitable biogeochemical environment for them to flourish.
    Description: Financial support for this work was provided by the Council of Scientific & Industrial Research (CSIR) and Ministry of Earth Sciences (MoES). S. Kurian acknowledges POGO-SCOR for financial support to visit WHOI. R. Roy, G. Narvenkar and A. Sarkar received fellowship support from CSIR. D. Repeta acknowledges support from US National Science Foundation Center Award EF0424599 to the Center for Microbial Oceanography: Research and Education (C-MORE).
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 9
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    Declining oxygen in the global ocean and coastal waters (2018)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 359 (6371). eaam7240.
    Details
    Publication Date: 2021-02-08
    Description: As plastic waste pollutes the oceans and fish stocks decline, unseen below the surface another problem grows: deoxygenation. Breitburg et al. review the evidence for the downward trajectory of oxygen levels in increasing areas of the open ocean and coastal waters. Rising nutrient loads coupled with climate change—each resulting from human activities—are changing ocean biogeochemistry and increasing oxygen consumption. This results in destabilization of sediments and fundamental shifts in the availability of key nutrients. In the short term, some compensatory effects may result in improvements in local fisheries, such as in cases where stocks are squeezed between the surface and elevated oxygen minimum zones. In the longer term, these conditions are unsustainable and may result in ecosystem collapses, which ultimately will cause societal and economic harm.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1126/science.aam7240
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    Marine hypoxia/anoxia as a source of CH4 and N2O (2010)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 7 . pp. 2159-2190.
    Details
    Publication Date: 2019-09-23
    Description: We review here the available information on methane (CH4) and nitrous oxide (N2O) from major marine, mostly coastal, oxygen (O2)-deficient zones formed both naturally and as a result of human activities (mainly eutrophication). Concentrations of both gases in subsurface waters are affected by ambient O2 levels to varying degrees. Organic matter supply to seafloor appears to be the primary factor controlling CH4 production in sediments and its supply to (and concentration in) overlying waters, with bottom-water O2-deficiency exerting only a modulating effect. High (micromolar level) CH4 accumulation occurs in anoxic (sulphidic) waters of silled basins, such as the Black Sea and Cariaco Basin, and over the highly productive Namibian shelf. In other regions experiencing various degrees of O2-deficiency (hypoxia to anoxia), CH4 concentrations vary from a few to hundreds of nanomolar levels. Since coastal O2-deficient zones are generally very productive and are sometimes located close to river mouths and submarine hydrocarbon seeps, it is difficult to differentiate any O2-deficiency-induced enhancement from in situ production of CH4 in the water column and its inputs through freshwater runoff or seepage from sediments. While the role of bottom-water O2-deficiency in CH4 formation appears to be secondary, even when CH4 accumulates in O2-deficient subsurface waters, methanotrophic activity severely restricts its diffusive efflux to the atmosphere. As a result, an intensification or expansion of coastal O2-deficient zones will probably not drastically change the present status where emission from the ocean as a whole forms an insignificant term in the atmospheric CH4 budget. The situation is different for N2O, the production of which is greatly enhanced in low-O2 waters, and although it is lost through denitrification in most suboxic and anoxic environments, the peripheries of such environments offer most suitable conditions for its production, with the exception of enclosed anoxic basins. Most O2-deficient systems serve as strong net sources of N2O to the atmosphere. This is especially true for coastal upwelling regions with shallow O2-deficient zones where a dramatic increase in N2O production often occurs in rapidly denitrifying waters. Nitrous oxide emissions from these zones are globally significant, and so their ongoing intensification and expansion is likely to lead to a significant increase in N2O emission from the ocean. However, a meaningful quantitative prediction of this increase is not possible at present because of continuing uncertainties concerning the formative pathways to N2O as well as insufficient data from key coastal regions.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/bg-7-2159-2010
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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