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    Impact of increasing carbon dioxide on dinitrogen and carbon fixation rates under oligotrophic conditions and simulated upwelling (2021)
    John Wiley & Sons, Inc. | Hoboken, USA
    Details
    Publication Date: 2021-09-29
    Description: Dinitrogen (N2) fixation is a major source of bioavailable nitrogen to oligotrophic ocean communities. Yet, we have limited understanding how ongoing climate change could alter N2 fixation. Most of our understanding is based on short‐term laboratory experiments conducted on individual N2‐fixing species whereas community‐level approaches are rare. In this longer‐term in situ mesocosm study, we aimed to improve our understanding on the role of rising atmospheric carbon dioxide (CO2) and simulated deep water upwelling on N2 and carbon (C) fixation rates in a natural oligotrophic plankton community. We deployed nine mesocosms in the subtropical North Atlantic Ocean and enriched seven of these with CO2 to yield a range of treatments (partial pressure of CO2, pCO2 = 352–1025 μatm). We measured rates of N2 and C fixation in both light and dark incubations over the 55‐day study period. High pCO2 negatively impacted light and dark N2 fixation rates in the oligotrophic phase before simulated upwelling, while the effect reversed in the light N2 fixation rates in the bloom decay phase after added nutrients were consumed. Dust deposition and simulated upwelling of nutrient‐rich deep water increased N2 fixation rates and nifH gene abundances of selected clades including the unicellular diazotrophic cyanobacterium clade UCYN‐B. Elevated pCO2 increased C fixation rates in the decay phase. We conclude that elevated pCO2 and pulses of upwelling have pronounced effects on diazotrophy and primary producers, and upwelling and dust deposition modify the pCO2 effect in natural assemblages.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Exzellenzcluster Ozean der Zukunft http://dx.doi.org/10.13039/501100010783
    Description: H2020 Environment http://dx.doi.org/10.13039/100010681
    Description: Villum Foundation http://dx.doi.org/10.13039/100008398
    Description: Horizon 2020 http://dx.doi.org/10.13039/100010661
    Description: Research Foundation http://dx.doi.org/10.13039/100005930
    Description: Federal Ministry of Education and Research http://dx.doi.org/10.13039/501100002347
    Keywords: 551 ; subtropical North Atlantic Ocean ; N2 fixation ; C fixation
    Type: map
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    CITATION GEO-LEO
  • 2
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    Counting (on) blue carbon—Challenges and ways forward for carbon accounting of ecosystem-based carbon removal in marine environments (2023)
    Public Library of Science (PLOS)
    Details
    Publication Date: 2024-02-07
    Description: The latest IPCC assessment report highlights once more the need for negative emissions via carbon dioxide removal (CDR) measures to reach ambitious mitigation goals. In particular ecosystem-based CDR measures are currently the focus of national net-zero strategies and novel carbon crediting efforts. Blue carbon dioxide removal (blueCDR) options are anthropogenic activities that aim to enhance such ecosystem-based carbon sinks in the marine environment. The protection and conservation of existing marine ecosystems that naturally sequester carbon, does not qualify as CDR. Using blueCDR as an example, we highlight key challenges concerning the monitoring and evaluation of marine carbon fluxes for carbon crediting. Challenges specific to ecosystem-based CDR measures are i) the definition of baseline natural carbon fluxes, which is necessary for ii) clear anthropogenic CDR signal attribution, as well as iii) accounting for possible natural or anthropogenic disturbances of the carbon stock and hence an assessment for the durability of the carbon storage. In addition, the marine environment poses further monitoring and evaluation challenges due to i) temporal and spatial decoupling of the carbon capturing and sequestration processes, combined with ii) signal dilution due to high ecosystem connectivity, and iii) large pre-existing carbon stocks which makes any human-made increase in carbon stocks even harder to quantify. To increase the scientific rigour and ensure additionality behind issued carbon credits, we support the current trend of focusing monitoring efforts on carbon sequestration rather than on capturing processes, and on establishing a baseline for natural carbon sequestration in diverse marine ecosystems. Finally, we believe that making carbon credits subject to dynamic adjustments over time, will increase their credibility.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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