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  • 1
    Publication Date: 2019-02-01
    Description: Subsurface coherent eddies are well-known features of ocean circulation, but the sparsity of observations prevents an assessment of their importance for biogeochemistry. Here, we use a global eddying (0.1° ) ocean-biogeochemical model to carry out a census of subsurface coherent eddies originating from eastern boundary upwelling systems (EBUS), and quantify their biogeochemical effects as they propagate westward into the subtropical gyres. While most eddies exist for a few months, moving over distances of 100s of km, a small fraction (〈 5%) of long-lived eddies propagates over distances greater than 1000km, carrying the oxygen-poor and nutrient-rich signature of EBUS into the gyre interiors. In the Pacific, transport by subsurface coherent eddies accounts for roughly 10% of the offshore transport of oxygen and nutrients in pycnocline waters. This "leakage" of subsurface waters can be a significant fraction of the transport by nutrient-rich poleward undercurrents, and may contribute to the well-known reduction of productivity by eddies in EBUS. Furthermore, at the density layer of their cores, eddies decrease climatological oxygen locally by close to 10%, thereby expanding oxygen minimum zones. Finally, eddies represent low-oxygen extreme events in otherwise oxygenated waters, increasing the area of hypoxic waters by several percent and producing dramatic short-term changes that may play an important ecological role. Capturing these non-local effects in global climate models, which typically include non-eddying oceans, would require dedicated parameterizations.
    Type: Article , PeerReviewed
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  • 2
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    Nature Publishing Group
    In:  Nature Geoscience, 11 (7). pp. 467-473.
    Publication Date: 2019-02-01
    Description: Direct observations indicate that the global ocean oxygen inventory is decreasing. Climate models consistently confirm this decline and predict continuing and accelerating ocean deoxygenation. However, current models (1) do not reproduce observed patterns for oxygen changes in the ocean’s thermocline; (2) underestimate the temporal variability of oxygen concentrations and air–sea fluxes inferred from time-series observations; and (3) generally simulate only about half the oceanic oxygen loss inferred from observations. We here review current knowledge about the mechanisms and drivers of oxygen changes and their variation with region and depth over the world’s oceans. Warming is considered a major driver: in part directly, via solubility effects, and in part indirectly, via changes in circulation, mixing and oxygen respiration. While solubility effects have been quantified and found to dominate deoxygenation near the surface, a quantitative understanding of contributions from other mechanisms is still lacking. Current models may underestimate deoxygenation because of unresolved transport processes, unaccounted for variations in respiratory oxygen demand, or missing biogeochemical feedbacks. Dedicated observational programmes are required to better constrain biological and physical processes and their representation in models to improve our understanding and predictions of patterns and intensity of future oxygen change.
    Type: Article , PeerReviewed
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  • 3
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    Peter Lang
    In:  In: Unsicherheit als Herausforderung für die Wissenschaft : Reflexionen aus Natur-, Sozial- und Geisteswissenschaften. , ed. by Janich, N. and Rhein, L. Peter Lang, Berlin, Germany, pp. 15-30. ISBN 978-3-631-76153-3
    Publication Date: 2018-08-27
    Description: The chapter discusses sources of uncertainties in climate models and their possible impacts on the model results. The three criteria “adequacy”, “consistency” and “representativeness” are suggested for a comprehensive assessment of the quality of climate models. The fit to data determines the model’s representativeness. For many climate variables, such as precipitation, cloudiness and the climate sensitivity, this has not significantly improved from the second-to-last to the last assessment report of the Intergovernmental Panel on Climate Change (IPCC). However, the level of detailed mechanistic descriptions has increased for a number of processes included in the models, yielding an improved adequacy of these models. Still, with current climate models being still unable to consistently reproduce glacial cycles driven only by orbital parameters, and with the amplitude of climate change expected until the end of the century being of similar amplitude as glacial-interglacial changes, there is still considerable uncertainty regarding how reliable current models’ projections of 21st century climate change can be. However, uncertainty must not hinder society to make informed decisions, and it is the responsibility of climate research to provide relevant information regarding the uncertainty of climate model projections.
    Type: Book chapter , NonPeerReviewed
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  • 4
    Publication Date: 2019-02-01
    Description: The Paris Agreement target of limiting global surface warming to 1.5–2∘C compared to pre-industrial levels by 2100 will still heavily impact the ocean. While ambitious mitigation and adaptation are both needed, the ocean provides major opportunities for action to reduce climate change globally and its impacts on vital ecosystems and ecosystem services. A comprehensive and systematic assessment of 13 global- and local-scale, ocean-based measures was performed to help steer the development and implementation of technologies and actions toward a sustainable outcome. We show that (1) all measures have tradeoffs and multiple criteria must be used for a comprehensive assessment of their potential, (2) greatest benefit is derived by combining global and local solutions, some of which could be implemented or scaled-up immediately, (3) some measures are too uncertain to be recommended yet, (4) political consistency must be achieved through effective cross-scale governance mechanisms, (5) scientific effort must focus on effectiveness, co-benefits, disbenefits, and costs of poorly tested as well as new and emerging measures.
    Type: Article , PeerReviewed
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  • 5
    Publication Date: 2019-04-18
    Description: Visible results were obtained by the working groups in Kiel on the first four aspects of the project, resulting in improvements of the quantitative knowledge of key processes and key regions in the Atlantic Ocean. New ocean and coupled ocean-atmosphere models were analyzed with regard to seasonal and decadal climate changes, as well as optimization techniques. In addition, the influence of circulation variability on oceanic CO2 uptake was investigated. Intense field studies were carried out successfully in two regions: The measurements obtained in the equatorial Atlantic serve as the basis for a better understanding of the role of the tropical Atlantic for climate fluctuations in the Atlantic in general, and also provide predictability indicators for seasonal forecasts. The second focal area of field work was the southern region of the Labrador Sea near 53°N where different components of the North Atlantic Deep Water merge to form the deep western boundary current (DWBC). Here a mooring array has been deployed for the past 13 years to monitor this branch of the thermohaline circulation exiting the Labrador Sea. In collaboration with other national and international large-scale observations (ship-based measurements, Argo floats, etc.) and modeling efforts, the field work carried out by the Kiel working groups provides a significant contribution toward a sustainable regional ocean-climate analysis system.
    Type: Book chapter , NonPeerReviewed
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  • 6
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    PANGAEA
    In:  Supplement to: Zamora, Lauren M; Oschlies, Andreas (2014): Surface nitrification: a major uncertainty in marine N2O emissions. Geophysical Research Letters, 41(12), 4247-4253, https://doi.org/10.1002/2014GL060556
    Publication Date: 2019-04-30
    Description: The ocean is responsible for up to a third of total global nitrous oxide (N2O) emissions, but uncertainties in emission rates of this potent greenhouse gas are high (〉100%). Here we use a marine biogeochemical model to assess six major uncertainties in estimates of N2O production, thereby providing guidance in how future studies may most effectively reduce uncertainties in current and future marine N2O emissions. Potential surface N2O production from nitrification causes the largest uncertainty in N2O emissions (estimated up to ~1.6 Tg N/yr, or 48% of modeled values), followed by the unknown oxygen concentration at which N2O production switches to N2O consumption (0.8 Tg N/yr, or 24% of modeled values). Other uncertainties are minor, cumulatively changing regional emissions by 〈15%. If production of N2O by surface nitrification could be ruled out in future studies, uncertainties in marine N2O emissions would be halved.
    Type: Dataset
    Format: application/zip, 52.0 MBytes
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  • 7
    Publication Date: 2017-06-13
    Description: The Ocean Model Intercomparison Project (OMIP) focuses on the physics and biogeochemistry of the ocean component of Earth system models participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6). OMIP aims to provide standard protocols and diagnostics for ocean models, while offering a forum to promote their common assessment and improvement. It also offers to compare solutions of the same ocean models when forced with reanalysis data (OMIP simulations) vs. when integrated within fully coupled Earth system models (CMIP6). Here we detail simulation protocols and diagnostics for OMIP’s biogeochemical and inert chemical tracers. These passive-tracer simulations will be coupled to ocean circulation models, initialized with observational data or output from a model spin-up, and forced by repeating the 1948– 2009 surface fluxes of heat, fresh water, and momentum. These so-called OMIP-BGC simulations include three inert chemical tracers (CFC-11, CFC-12, SF6) and biogeochemical tracers (e.g., dissolved inorganic carbon, carbon isotopes, alkalinity, nutrients, and oxygen). Modelers will use their preferred prognostic BGC model but should follow common guidelines for gas exchange and carbonate chemistry. Simulations include both natural and total carbon tracers. The required forced simulation (omip1) will be initialized with gridded observational climatologies. An optional forced simulation (omip1-spunup) will be initialized instead with BGC fields from a long model spin-up, preferably for 2000 years or more, and forced by repeating the same 62-year meteorological forcing. That optional run will also include abiotic tracers of total dissolved inorganic carbon and radiocarbon, Cabio T and 14Cabio T , to assess deep-ocean ventilation and distinguish the role of physics vs. biology. These simulations will be forced by observed atmospheric histories of the three inert gases and CO2 as well as carbon isotope ratios of CO2. OMIP-BGC simulation protocols are founded on those from previous phases of the Ocean Carbon-Cycle Model Intercomparison Project. They have been merged and updated to reflect improvements concerning gas exchange, carbonate chemistry, and new data for initial conditions and atmospheric gas histories. Code is provided to facilitate their implementation.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 8
  • 9
    ISSN: 1359-0189
    Keywords: Earthquake Research ; LR 115 ; Radon ; alpha-meter
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Type of Medium: Electronic Resource
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  • 10
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    AGU / Wiley
    In:  Journal of Geophysical Research: Oceans, 110 . C07S01.
    Publication Date: 2018-04-18
    Description: Conducted in the northeast Atlantic Ocean (15°20′–21°20′W, 38°N–45°N), the Programme Océan Multidisciplinaire Méso Echelle (POMME) is a research project aimed at a better understanding of the biological production and the carbon budget of the region in relation to the formation mechanisms of the 11°–12°C mode water of the northeast Atlantic. With the help of two research vessels, several tens of floats and drifters, and nine moorings, the field experiment was carried out between autumn 2000 and autumn 2001, with a more intensive phase in the winter and early spring of 2001. The field experiment resolved small (several kilometers) to regional (several hundred kilometers) scales and daily to seasonal variability. A first analysis of the rich data set focused on the large-scale and the mesoscale variability. It shows that the distribution of water mass characteristics and biological activity is strongly influenced by the mesoscales in this supposedly quiet transition zone between the subtropical and subpolar gyres. The seasonal variability, however, presents an imprint of the large-scale structures with a clear north-south gradient in properties and budgets. This region is found on an annual average to be a sink of atmospheric CO2. Smaller scales, associated with fronts and filaments, were clearly observed in many fields (temperature, but also chlorophyll, oxygen, biogenic particles, etc.), with modeling studies suggesting that they play a significant role in subduction, ventilation, and transport of biogeochemical tracers in the POMME region.
    Type: Article , PeerReviewed
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