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  • 1
    Electronic Resource
    Electronic Resource
    Ring-strain-modified properties of substituted perylene radical cation salts. A solid-state carbon-13 CPMAS NMR study (1990)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 112 (1990), S. 8285-8292 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00179a011
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    Paper (German National Licenses)
    Fulltext
  • 2
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    Influence of mesoscale eddies on biological production in the Mozambique Channel: Several contrasted examples from a coupled ocean-biogeochemistry model (2014)
    Elsevier
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 100 . pp. 79-93.
    Details
    Publication Date: 2015-01-12
    Description: The impact of mesoscale activity on phytoplankton and nutrient distribution in the Mozambique Channel was simulated by coupling a biogeochemical model (PISCES) with a regional oceanic model (ROMS). Examples of the effects of eddies on the biogeochemistry of the Mozambique Channel are presented to illustrate the complexity of the system. In the model, several cyclonic eddies were found with low concentrations of chlorophyll at their cores, which contrasts with previous studies in the open ocean. In addition, several anticyclonic eddies were simulated with high concentrations of chlorophyll at their cores. Phytoplankton growth within these mesoscale features (both cyclonic and anticyclonic eddies) occurred in response to nutrient injection into the euphotic zone by advection, and subsequent retention of surrounding nutrient-rich waters within eddies. Offshore nutrient distributions depended strongly on lateral advection of nutrient-rich water from the coastal regions, induced by eddy interaction with the shelf. The environmental conditions at the locations where eddies were generated had an important effect on nutrient concentrations within these structures.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.dsr2.2013.10.018
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Suppressing and enhancing effects of mesoscale dynamics on biological production in the Mozambique Channel (2016)
    Elsevier
    In:  Journal of Marine Systems, 158 . pp. 129-139.
    Details
    Publication Date: 2019-02-01
    Description: We used a coupled physical–biogeochemical model to investigate how the strong eddy activity typical of the Mozambique Channel affects biological production. A numerical experiment was carried out, in which mesoscale dynamics were suppressed by cancelling the nonlinear terms for horizontal momentum in the Naviers–Stokes equation. Mesoscale dynamics were found to be responsible for (1) increased offshore production in the Mozambique Channel as a result of net eddy-induced offshore transport of nutrient-rich coastal waters; (2) decreased shelf production along the central Mozambican and south-west Madagascar coast caused by a reduction in nutrient availability related to the net eddy-induced lateral transport of nutrients; (3) increased coastal production along the northern Mozambican coast caused by eddy-induced nutrient supply. The model results also showed an intensification and shallowing of the subsurface production, related to increased upper layer nutrient concentrations caused by eddy activity. In addition, by driving the detachment of the East Madagascar Current at the southern tip of the island, inertial processes intensify the southern Madagascar upwelling and causes offshore diffusion of the upwelled waters. These results emphasize the complex role played by eddy activity and, more generally, inertial processes on marine ecosystems in this region.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.jmarsys.2016.02.003
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    A Model Investigation of the Influences of the South‐East Madagascar Current on the South‐East Madagascar Bloom (2020)
    AGU (American Geophysical Union)
    Details
    Publication Date: 2023-02-08
    Description: The South-East Madagascar Bloom, one of the most compelling biogeochemical features of the Indian Ocean, occurs sporadically during austral summer in the oligotrophic waters south-east of Madagascar, where it can cover up to 1% of the global ocean surface area. Its spatial extension and its timing are highly variable. A high-resolution biophysical model is used to investigate a previous hypothesis that the onset of a particular circulation of the South-East Madagascar Current advects fresher and nutrient-rich waters eastward, feeding the bloom. The model is able to reproduce an intermittent phytoplankton bloom with large spatial variability but in the subsurface layers, as well as the presence of an irregular retroflection of the South-East Madagascar Current. The simulated bloom occurs within a shallow stratified mixed layer, with fresher waters at the surface, parallel to the water mass in an observed bloom. The model results suggest, from a nutrient flux analysis, that horizontal advection of low-salinity nutrient-rich Madagascan coastal waters can indeed trigger a phytoplankton bloom. The coupled model is also able to resolve a bloom that is atmospherically forced by cyclonic activity.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    A New Definition of the South‐East Madagascar Bloom and Analysis of Its Variability (2019)
    Wiley | AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 124 (3). pp. 1717-1735.
    Details
    Publication Date: 2022-01-31
    Description: The South-East Madagascar Bloom occurs in an oligotrophic region of the southwest Indian Ocean. Phase locked to austral summer, this sporadic feature exhibits substantial temporal and spatial variability. Several studies, with different hypotheses, have focused on the initiation mechanism triggering the bloom, but none has been as yet clearly substantiated. With 19 years of ocean color data set available as well as in situ measurements (Argo profiles), the time is ripe to review this feature. The bloom is characterized in a novel manner, and a new bloom index is suggested, yielding 11 bloom years, including 3 major bloom years (1999, 2006, and 2008). Spatially, the bloom varies from a mean structure (22–32°S; 50–70°E) both zonally and meridionally. A colocation analysis of Argo profiles and chlorophyll-a data revealed a bloom occurrence in a shallow-stratified layer, with low-salinity water in the surface layers. Additionally, a quantitative assessment of the previous hypotheses is performed and bloom occurrence is found to coincide with La Niña events and reduced upwelling intensity south of Madagascar. A stronger South-East Madagascar Current during La Niña may support a detachment of the current from the coasts, dampening the upwelling south of Madagascar, and feeding low-salinity waters into the Madagascar Basin, hence increasing stratification. Along with abundance of light, these provide the right conditions for a nitrogen-fixing cyanobacterial phytoplankton bloom onset
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2018JC014582
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    On the role of the Agulhas system in ocean circulation and climate (2011)
    Nature Publishing Group
    Details
    Publication Date: 2022-02-18
    Description: The Atlantic Ocean receives warm, saline water from the Indo-Pacific Ocean through Agulhas leakage around the southern tip of Africa. Recent findings suggest that Agulhas leakage is a crucial component of the climate system and that ongoing increases in leakage under anthropogenic warming could strengthen the Atlantic overturning circulation at a time when warming and accelerated meltwater input in the North Atlantic is predicted to weaken it. Yet in comparison with processes in the North Atlantic, the overall Agulhas system is largely overlooked as a potential climate trigger or feedback mechanism. Detailed modelling experiments—backed by palaeoceanographic and sustained modern observations—are required to establish firmly the role of the Agulhas system in a warming climate.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Where and How the East Madagascar Current Retroflection Originates? (2021)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-02-07
    Description: The East Madagascar Current (EMC) is one of the western boundary currents of the South Indian Ocean. As such, it plays an important role in the climate system by transporting water and heat toward the pole and recirculating to the large-scale Indian Ocean through retroflection modes of its southern extension. Five cruise data sets and remote sensing data from different sensors are used to identify three states of the southern extension of the EMC: early retroflection, canonical retroflection, and no retroflection. Retroflections occur 47% of the time. EMC strength regulates the retroflection state, although impinged mesoscale eddies also contribute to retroflection formation. Early retroflection is linked with EMC volume transport. Anticyclonic eddies drifting from the central Indian Ocean to the coast favor early retroflection formation, anticyclonic eddies near the southern tip of Madagascar promote the generation of canonical retroflection, and no retroflection appears to be associated with a lower eddy kinetic energy (EKE). Knowledge of the EMC retroflection state could help predict (a) coastal upwelling south of Madagascar, (b) the southeastern Madagascar phytoplankton bloom, and (c) the formation of the South Indian Ocean Counter Current (SICC).
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    New insights on the upper layer circulation north of the Gulf of Guinea (2016)
    Wiley-Blackwell
    Details
    Publication Date: 2016-08-30
    Description: The oceanic circulation in the upper layers of the north of the Gulf of Guinea is analyzed, as inferred from in situ observations and numerical simulations. This particular region, in spite of the presence of a coastal upwelling and its impact on resources and regional climate, is still poorly documented. Cruises carried out in the framework of different international programs (e.g. EGEE/AMMA, PIRATA) allowed to show the existence of an eastward flowing undercurrent, found under the Guinea Current, named the Guinea UnderCurrent (GUC). Numerical results from high resolution simulation allowed the description of the seasonal variability of this current. It appears that the GUC is stronger in spring and reverses westward in August-September. We also depict the fate and the sources of the GUC based on selected trajectories from numerical particle tracking. The simulated trajectories reveal: i) a preferred route of the GUC along 4°N from Cape Palmas to Cape Three Points and following the coast east of Cape Three Points; ii) strong recirculations in the most eastern part of the Gulf of Guinea and off Cape Palmas including warm and salty waters of the South Equatorial Current; iv) a weak inflow from northern latitudes through a subsurface current flowing southward along the West African coast. In addition, Lagrangian experiments show that the GUC is not an extension of the North Equatorial UnderCurrent and confirm that this current does not penetrate into the Gulf of Guinea. This article is protected by copyright. All rights reserved.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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