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  • 1
    Keywords: Hochschulschrift
    Type of Medium: Online Resource
    Pages: Online-Ressource (81 Seiten = 14 MB) , Illustrationen, Graphen
    Language: German
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  • 2
    Online Resource
    Online Resource
    [Kiel] : [GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel]
    Keywords: Forschungsbericht ; Meerwasser ; Kohlendioxid ; Versauerung ; Biogeochemie
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (236 Seiten, 5,3 MB) , Illustrationen, Diagramme
    Language: German
    Note: Förderkennzeichen BMBF 03F0728A-H - 03F0728J-K. - Verbund-Nummer 01162212 , Autoren dem Berichtsblatt entnommen , Unterschiede zwischen dem gedruckten Dokument und der elektronischen Ressource können nicht ausgeschlossen werden , Sprache der Zusammenfassung: Deutsch, Englisch
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  • 3
    In: Journal of climate, Boston, Mass. [u.a.] : AMS, 1988, 21(2008), 24, Seite 6599-6615, 1520-0442
    In: volume:21
    In: year:2008
    In: number:24
    In: pages:6599-6615
    Description / Table of Contents: The causes and characteristics of interannualdecadal variability of the meridional overturning circulation (MOC) in the North Atlantic are investigated with a suite of basin-scale ocean models [the Family of Linked Atlantic Model Experiments (FLAME)] and global oceanice models (ORCA), varying in resolution from medium to eddy resolving (1/2ʿ1/12ʿ), using various forcing configurations built on bulk formulations invoking atmospheric reanalysis products. Comparison of the model hindcasts indicates similar MOC variability characteristics on time scales up to a decade; both model architectures also simulate an upward trend in MOC strength between the early 1970s and mid-1990s. The causes of the MOC changes are examined by perturbation experiments aimed selectively at the response to individual forcing components. The solutions emphasize an inherently linear character of the midlatitude MOC variability by demonstrating that the anomalies of a (noneddy resolving) hindcast simulation can be understood as a superposition of decadal and longer-term signals originating from thermohaline forcing variability, and a higher-frequency wind-driven variability. The thermohaline MOC signal is linked to the variability in subarctic deep-water formation, and rapidly progressing to the tropical Atlantic. However, throughout the subtropical and midlatitude North Atlantic, this signal is effectively masked by stronger MOC variability related to wind forcing and, especially north of 30ʿ-35ʿN, by internally induced (eddy) fluctuations.
    Type of Medium: Online Resource
    Pages: graph. Darst
    ISSN: 1520-0442
    Language: English
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  • 4
    Publication Date: 2023-05-12
    Description: Here we provide optimised vertical eddy diffusivity estimates for the PeECE III and KOSMOS 2013 mesocosm experiment, obtained from a model-based reanalysis. These diffusivities are derived from the observed temperature and salinity profiles that have been published in Schulz et al., 2008. Furthermore, we make our model code available, providing an adjustable tool to simulate vertical mixing in any other pelagic mesocosm. We also provide the interpolated and regridded temperature and salinity profiles of the PeECE III experiment as well as the density profiles which we calculated from the temperature and salinity profiles using the R package seacarb (Lavigne et al., 2011). These data files are required as input to run simulations of the PeECE III experiment with the 1D mesocosm mixing model. The columns of the environmental files (required input files for the model) from left to right are: Experiment year, month, day, Julian day, photosynthetically active radiation (PAR) [W/m^2], temperature [C], salinity [PSU], CO2 concentration [ppm], wind speed [m/s]. The rows list the respective value of each hour of the experiment. Temperature and salinity in this table are hourly interpolated values of the daily measurements published by the PeECE III team (2005). PAR has been calculated from global radiation data of Bergen provided by Olseth et al., 2005. In the temperature, salinity and density files, the rows indicate the depth (0.5 m resolution, the first row is the surface, the last row is the bottom), whereas the columns indicate the experiment time at an hourly resolution.
    Keywords: File content; File format; File name; File size; Uniform resource locator/link to file
    Type: Dataset
    Format: text/tab-separated-values, 20 data points
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  • 5
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    AGU (American Geophysical Union) | Wiley
    In:  Global Biogeochemical Cycles, 31 (11). pp. 1656-1673.
    Publication Date: 2020-02-06
    Description: In this pilot study we link the yield of industrial fisheries to changes in the zooplankton mortality in an idealized way accounting for different target species (planktivorous fish—decreased zooplankton mortality; large predators—increased zooplankton mortality). This indirect approach is used in a global coupled biogeochemistry circulation model to estimate the range of the potential impact of industrial fisheries on marine biogeochemistry. The simulated globally integrated response on phytoplankton and primary production is in line with expectations—a high (low) zooplankton mortality results in a decrease (increase) of zooplankton and an increase (decrease) of phytoplankton. In contrast, the local response of zooplankton and phytoplankton depends on the region under consideration: In nutrient-limited regions, an increase (decrease) in zooplankton mortality leads to a decrease (increase) in both zooplankton and phytoplankton biomass. In contrast, in nutrient-replete regions, such as upwelling regions, we find an opposing response: an increase (decrease) of the zooplankton mortality leads to an increase (decrease) in both zooplankton and phytoplankton biomass. The results are further evaluated by relating the potential fisheries-induced changes in zooplankton mortality to those driven by CO2 emissions in a business-as-usual 21st century emission scenario. In our idealized case, the potential fisheries-induced impact can be of similar size as warming-induced changes in marine biogeochemistry.
    Type: Article , PeerReviewed
    Format: text
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  • 6
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    The Royal Society
    In:  Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 375 (2102). p. 20160325.
    Publication Date: 2020-02-06
    Description: Observational estimates and numerical models both indicate a significant overall decline in marine oxygen levels over the past few decades. Spatial patterns of oxygen change, however, differ considerably between observed and modelled estimates. Particularly in the tropical thermocline that hosts open-ocean oxygen minimum zones, observations indicate a general oxygen decline, whereas most of the state-of-the-art models simulate increasing oxygen levels. Possible reasons for the apparent model-data discrepancies are examined. In order to attribute observed historical variations in oxygen levels, we here study mechanisms of changes in oxygen supply and consumption with sensitivity model simulations. Specifically, the role of equatorial jets, of lateral and diapycnal mixing processes, of changes in the wind-driven circulation and atmospheric nutrient supply, and of some poorly constrained biogeochemical processes are investigated. Predominantly wind-driven changes in the low-latitude oceanic ventilation are identified as a possible factor contributing to observed oxygen changes in the low-latitude thermocline during the past decades, while the potential role of biogeochemical processes remains difficult to constrain. We discuss implications for the attribution of observed oxygen changes to anthropogenic impacts and research priorities that may help to improve our mechanistic understanding of oxygen changes and the quality of projections into a changing future.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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  • 7
    Publication Date: 2019-09-23
    Description: We present a robust method for diagnosing total diapycnal diffusivities, i.e. explicitly applied plus numerically induced diffusivities, from tracer release experiments in numerical z-level models. To this extent, numerical experiments differing only in the advection scheme used (CTRD using 2nd order centred differences, UPWIND using the upwind/upstream advection scheme, QUICK using the quicker advection scheme after Farrow and Stevens (1995) and FCT after Gerdes et al. (1991)) are analysed and compared. To obtain regionally resolved estimates of diapycnal diffusivities, individual inert dye tracers are released in dynamically different regions of a North Atlantic model, namely (i) in the interior of the subtropical gyre and (ii) in the western boundary current. Diagnosed diffusivities are robust with respect to changes in temporal and spatial sampling of the simulated dye tracer for both advection schemes and for both regions. The numerically induced diffusivity is generally positive, but can become negative for centred differences advection numerics after several months of simulated tracer dispersion.
    Type: Article , PeerReviewed
    Format: text
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  • 8
    Publication Date: 2019-09-23
    Description: Diapycnal diffusion is a key process in the ocean, responsible for water mass transformation and the conversion of kinetic energy into potential energy. Despite its widely assumed importance in controlling ocean dynamics, diapycnal diffusion is difficult to quantify both in the real ocean and in ocean models. Here we focus on z-level models, arguably the most common vertical grid scheme of current ocean general circulation models. We examine different methods to diagnose diapycnal diffusivities in z-level models. Different scenarios are investigated, including the impact of advection and vertical convergence or divergence of isopycnals. In all cases we find that the transformation from z-space to density space has to be performed very carefully in order to obtain reliable and robust estimates of diapycnal diffusivities (and the associated diapycnal fluxes). A method involving the tracer flux taken from the work of Griffies et al. (2000) seems to be most appropriate in this respect and is suggested as our method of choice for subsequent applications to 3-dimensional ocean circulation models
    Type: Article , PeerReviewed
    Format: text
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  • 9
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    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 43 (2). pp. 728-734.
    Publication Date: 2019-09-23
    Description: A coupled ocean biogeochemistry-circulation model is used to investigate the impact of observed past and anticipated future wind changes in the southern hemisphere on the oxygen minimum zone in the tropical Pacific. We consider the industrial period until the end of the 21st century and distinguish effects due to a strengthening of the westerlies from effects of a southward shift of the westerlies that is accompanied by a poleward expansion of the tropical trade winds. Our model results show that a strengthening of the westerlies counteracts part of the warming-induced decline in the global marine oxygen inventory. A poleward shift of the trade-westerlies boundary, however, triggers a significant decrease of oxygen in the tropical oxygen minimum zone. In a business-as-usual CO2 emission scenario, the poleward shift of the trade-westerlies boundary and warming-induced increase in stratification contribute equally to the expansion of suboxic waters in the tropical Pacific.
    Type: Article , PeerReviewed
    Format: text
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  • 10
    Publication Date: 2020-02-06
    Description: The Southern Ocean is a major sink for anthropogenic carbon. Yet, there is no quantitative consensus about how this sink will change when surface winds increase (as they are anticipated to do). Among the tools employed to quantify carbon uptake are global coupled ocean-circulation biogeochemical models. Because of computational limitations these models still fail to resolve potentially-important spatial scales. Instead, processes on these scales are parameterized. There is concern that deficiencies in these so-called eddy-parameterizations might imprint wrong sensitivities of projected oceanic carbon uptake. Here, we compare natural carbon uptake in the Southern Ocean simulated with contemporary eddy-parameterizations. We find that very differing parameterizations yield surprisingly similar oceanic carbon in response to strengthening winds. In contrast, we find (in an additional simulation) that the carbon uptake does differ substantially when the supply of bioavailable iron is altered within its envelope of uncertainty. We conclude that a more comprehensive understanding of bioavailable iron dynamics will substantially reduce the uncertainty of model-based projections of oceanic carbon uptake.
    Type: Article , PeerReviewed
    Format: text
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