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  • 1
    Publication Date: 2018-03-13
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 2
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    In:  [Talk] In: Goldschmidt Conference 2011, 14.-19.08.2011, Prague, Czech Republic .
    Publication Date: 2012-04-18
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 3
    Publication Date: 2012-03-15
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 4
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    In:  [Poster] In: 2012 Ocean Sciences Meeting, OSM, 20.02.-24.02.2012, Salt Lake City, Utah, USA . 2012 Ocean Sciences Meeting : abstract book ; February 20-24. 2012 ; Salt Palace Convention Center, Salt Lake City, Utah, USA ; ID 10110 .
    Publication Date: 2012-11-29
    Description: Abstract ID: 10110 PosterID: B1276 We measured for the first time seawater δ30SiSi(OH)4 and δ30SiBSi to examine sources and utilization of Si(OH)4 in the northern South China Sea (NSCS). δ30SiBSi values were systematically lower than the correspondingδ30SiSi(OH)4 in the euphotic zone (〈 100 m) on the shelf and slope. In contrast, δ30SiBSi were equal to δ30SiSi(OH)4 in the surface mixed layer (〈 50 m) of the deep basin and δ30SiBSi in waters below were significantly higher than the corresponding δ30SiSi(OH)4. By comparing the field data with calculation according to Rayleigh or steady state models, we demonstrated surface waters on the inner shelf were largely fed by nutrients from the Pearl River input. While the primary Si(OH)4 source for the euphotic zone on the outer shelf and slope was upwelling or mixing from underlying waters, the Si(OH)4 in the surface mixed layer of the NSCS basin might originate from horizontal mixing with highly fractionated waters. As a consequence, the Si isotope dynamics in the NSCS are largely modulated by variable biological fractionation of Si derived from different mixing-induced initial conditions rather than any single source water.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 5
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    In:  [Talk] In: EGU General Assembly 2011, 03.-08.04.2011, Vienna, Austria .
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 6
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    In:  [Poster] In: 2012 Ocean Sciences Meeting, OSM, 20.02.-24.02.2012, Salt Lake City, Utah, USA . 2012 Ocean Sciences Meeting : abstract book ; February 20-24. 2012 ; Salt Palace Convention Center, Salt Lake City, Utah, USA ; ID 10946 .
    Publication Date: 2012-04-13
    Description: Abstract ID: 10946 PosterID: B1569 In this study we present the first direct comparison between dissolved stable silicon (δ³⁰Si(OH)₄) and nitrogen (δ¹⁵NO₃-) isotopes in the upwelling area off Peru to investigate biogeochemical processes and nutrient cycling in one of the globally largest Oxygen Minimum Zones (OMZ). Silicon and nitrogen isotopes in the euphotic zone of the open ocean are mainly influenced by utilization in the way that diatoms preferentially incorporate the lighter isotopes, whereas in regions with prevailing anoxic waters the nitrate isotope composition is also altered by other processes. Silicic acid limitation offshore is indicated by high NO₃-:Si(OH)₄ ratios (~15) leading to the highest δ³⁰Si(OH)₄ values (3.7‰) accompanied by high δ¹⁵NO₃- values (16‰). Due to upwelling and intense recycling of silicic acid on the shelf, surface samples show low δ³⁰Si(OH)₄ values around 2‰. Nitrate isotope compositions in surface waters differ from values expected from δ³⁰Si(OH)₄ suggesting that either N-loss (denitrification and/or anammox) processes cause enrichment of heavy N-isotopes in the source waters of the upwelling, or the utilization of different N species derived from N₂-fixation or the utilization of ammonia occurs.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 7
    Publication Date: 2018-04-09
    Description: For this study two sediment cores from the Peruvian shelf covering the time period between the Little Ice Age (LIA) and present were examined for changes in productivity (biogenic opal concentrations (bSi)), nutrient utilisation (stable isotope compositions of silicon (δ30Siopal) and nitrogen (δ15Nsed)), as well as in ocean circulation and material transport (authigenic and detrital radiogenic neodymium (εNd) and strontium (87Sr/86Sr) isotopes). For the LIA the proxies recorded weak primary productivity and nutrient utilisation reflected by low average bSi concentrations of ~10%, δ15Nsed values of ~ +5‰ and intermediate δ30Siopal values of ~+0.97‰. At the same time the radiogenic isotope composition of the detrital sediment fraction indicates dominant local riverine input of lithogenic material due to higher rainfall in the Andean hinterland. These patterns were caused by permanent El Niño-like conditions characterized by a deeper nutricline, weak upwelling and low nutrient supply. At the end of the LIA, δ30Siopal dropped to low values of +0.6‰ and opal productivity reached its minimum of the past 650 years. During the following transitional period of time the intensity of upwelling, nutrient supply and productivity increased abruptly as marked by the highest bSi contents of up to 38%, by δ15Nsed of up to ~ +7‰, and by the highest degree of silicate utilisation with δ30Siopal reaching values of +1.1‰. At the same time detrital εNd and 87Sr/86Sr signatures documented increased wind strength and supply of dust to the shelf due to drier conditions. Since about 1870, productivity has been high but nutrient utilisation has remained at levels similar to the LIA indicating significantly increased nutrient availability. Comparison between the δ30Siopal and δ15Nsed signatures suggests that during the past 650 years the δ15Nsed signature in the Peruvian Upwelling area has most likely primarily been controlled by surface water utilisation and not, as previously assumed, by subsurface nitrogen loss processes in the water column.
    Type: Article , PeerReviewed
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    Format: text
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  • 8
    Publication Date: 2019-02-01
    Description: In this study we combine for the first time silicon (Si) isotope compositions of small mixed diatom species (δ30SibSiO2) and of large handpicked mono-generic (i.e. genus = Coscinodiscus) diatom samples (δ30SiCoscino) with diatom assemblages extracted from marine sediments in the Peruvian upwelling region in order to constrain present and past silicate utilisation. The extension of a previous core-top data set from the Peruvian shelf demonstrates that δ30SiCoscino values record near-complete Si utilisation, as these are similar to the isotopic composition of the subsurface source waters feeding the upwelling. In contrast, the δ30SibSiO2 of small mixed diatom species increase southward along the shelf as well as towards the shore. We attribute highest δ30SibSiO2 values partly to transient iron limitation but primarily to the gradual increase of Si isotope fractionation within the seasonal diatom succession, which are mainly recorded by small diatom species during intense bloom events. In contrast, lower δ30SibSiO2 values are related to initial Si isotope utilisation during periods of weak upwelling, when low Si(OH)4 concentrations do not permit intense blooms and small diatom species record substantially lower δ30Si signatures. As such, we propose that the intensity of the upwelling can be deduced from the offset between δ30SibSiO2 and δ30SiCoscino (Δ30Sicoscino–bSiO2), which is low for strong upwelling conditions and high for prevailing weak upwelling. We apply the information extracted from surface sediments to generate a record of the present-day main upwelling region covering the past 17,700 years and find that this location has also been characterized by a persistent offset (Δ30Sicoscino–bSiO2). By comparison with the diatom assemblages we show that the coastal upwelling system changed markedly between weak and strong upwelling conditions. In addition, our model calculations to quantify species-specific Si isotope fractionation effects based on the diatom assemblages indicate an overall minor influence that cannot explain the high amplitude in the measured δ30SibSiO2 record.
    Type: Article , PeerReviewed
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  • 9
    Publication Date: 2018-09-18
    Description: The Sustainable Development Goal for the oceans and coasts (SDG 14) as part of the 2030 Agenda can be considered as an important step towards achieving more comprehensive blue growth. Here, we selected a set of 18 indicators to measure progress against SDG 14 for EU coastal states in the Baltic and the North Sea and the Atlantic Ocean since 2012. In our assessment we distinguish between a concept of weak and strong sustainability, assuming high and low substitution possibilities, respectively. Overall, we show that the majority of countries in our assessment fail to achieve comprehensive blue growth. Sweden, Spain, Ireland, and in particular Portugal experienced a considerable reduction in scores since 2012. The only exemption is Estonia which managed to improve its scores over time under both concepts of sustainability. The unsustainable development at the EU level is mainly driven by deteriorations in indicators related to fisheries.
    Keywords: Q01 ; Q22 ; Q56 ; ddc:330 ; Sustainable Development Goals ; Blue Growth ; European Union ; Fisheries
    Repository Name: EconStor: OA server of the German National Library of Economics - Leibniz Information Centre for Economics
    Language: English
    Type: doc-type:workingPaper
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  • 10
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    In:  [Talk] In: Silicamics Conference 2018, 06.06.-09.06.2018, Victoria, Canada .
    Publication Date: 2018-12-14
    Type: Conference or Workshop Item , NonPeerReviewed
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