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  • 1
    Publication Date: 2022-06-28
    Description: The MSM89 expedition of Maria S Merian was a contribution to the international research initiative EUREC4A (www.eurec4a.eu). The cruise was carried out in concert with the M161 campaign on RV METEOR (Germany) and the EUREC4A-OA campaign on NO L’ATALANTE (France). Airplane and drone operations as well as well as continuous observations from the ground-based site on the Island of Barbados (BCO) were considered during the MSM89 campaign. Moreover, the cruise was coordinated with ships and Saildrone© operations in the context of the US American ATOMIC project. The overall goal of the EUREC4A field campaign was to collect observational data that will enable research on dynamic and thermodynamic processes in the atmosphere and ocean that will bring the understanding of the role of clouds in the climate system to a new level. MSM89 had its focus on the ocean/atmosphere coupling across ocean mesoscale vortices. For this purpose, both ocean and atmosphere profile measurements were carried out to observe the temporal evolution and spatial heterogeneity of the atmospheric and oceanic boundary layer. Autonomous observing platforms (underwater glider) and a ship towed platform (Cloudkite) augmented the ship-based observations. Incubation experiments were performed to determine Nitrogen fixation rates, the gas exchange for carbon dioxide and oxygen uptake.
    Type: Report , NonPeerReviewed
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  • 2
    Publication Date: 2019-09-23
    Type: Report , NonPeerReviewed , info:eu-repo/semantics/book
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  • 3
    Publication Date: 2020-04-20
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 4
    Publication Date: 2022-10-11
    Description: The Angolan shelf system represents a highly productive ecosystem. Throughout the year sea surface temperatures (SSTs) are cooler near the coast than further offshore. Lowest SSTs, the strongest cross-shore temperature gradient and maximum productivity occur in austral winter when seasonally prevailing upwelling favourable winds are weakest. Here, we investigate the seasonal mixed layer heat budget to analyse atmospheric and oceanic causes for heat content variability. By using different satellite and in-situ data, we derive monthly estimates of surface heat fluxes, mean horizontal advection and local heat content change. We calculate the heat budgets for the near coastal and offshore regions separately to explore processes that lead to the observed differences. The results show that the net surface heat flux warms the coastal ocean stronger than further offshore thus acting to damp spatial SST differences. Mean horizontal heat advection is dominated by meridional advection of warm water along the Angolan coast. However, its contribution to the heat budget is small. Ocean turbulence data suggests that the heat flux due to turbulent mixing across the base of the mixed layer is an important cooling term. This turbulent cooling that is strongest in shallow shelf regions is capable of explaining the observed negative cross-shore temperature gradient. The residuum of the mixed layer heat budget and uncertainties of budget terms are discussed.
    Type: Article , NonPeerReviewed , info:eu-repo/semantics/article
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  • 5
    Publication Date: 2022-01-19
    Type: Report , NonPeerReviewed
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  • 6
    Publication Date: 2024-02-07
    Description: In this paper, we review observational and modelling results on the upwelling in the tropical Atlantic between 10∘ N and 20∘ S. We focus on the physical processes that drive the seasonal variability of surface cooling and the upward nutrient flux required to explain the seasonality of biological productivity. We separately consider the equatorial upwelling system, the coastal upwelling system of the Gulf of Guinea and the tropical Angolan upwelling system. All three tropical Atlantic upwelling systems have in common a strong seasonal cycle, with peak biological productivity during boreal summer. However, the physical processes driving the upwelling vary between the three systems. For the equatorial regime, we discuss the wind forcing of upwelling velocity and turbulent mixing, as well as the underlying dynamics responsible for thermocline movements and current structure. The coastal upwelling system in the Gulf of Guinea is located along its northern boundary and is driven by both local and remote forcing. Particular emphasis is placed on the Guinea Current, its separation from the coast and the shape of the coastline. For the tropical Angolan upwelling, we show that this system is not driven by local winds but instead results from the combined effect of coastally trapped waves, surface heat and freshwater fluxes, and turbulent mixing. Finally, we review recent changes in the upwelling systems associated with climate variability and global warming and address possible responses of upwelling systems in future scenarios.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 7
    Publication Date: 2024-02-07
    Description: The science guiding the EUREC4A campaign and its measurements is presented. EUREC4A comprised roughly 5 weeks of measurements in the downstream winter trades of the North Atlantic – eastward and southeastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, EUREC4A marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or the life cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso- (200 km) and larger (500 km) scales, roughly 400 h of flight time by four heavily instrumented research aircraft; four global-class research vessels; an advanced ground-based cloud observatory; scores of autonomous observing platforms operating in the upper ocean (nearly 10 000 profiles), lower atmosphere (continuous profiling), and along the air–sea interface; a network of water stable isotopologue measurements; targeted tasking of satellite remote sensing; and modeling with a new generation of weather and climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that EUREC4A explored – from North Brazil Current rings to turbulence-induced clustering of cloud droplets and its influence on warm-rain formation – are presented along with an overview of EUREC4A's outreach activities, environmental impact, and guidelines for scientific practice. Track data for all platforms are standardized and accessible at https://doi.org/10.25326/165 (Stevens, 2021), and a film documenting the campaign is provided as a video supplement.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: video
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  • 8
    Publication Date: 2024-02-07
    Description: The Angolan shelf system represents a highly productive ecosystem. Throughout the year sea surface temperatures (SSTs) are cooler near the coast than further offshore. Lowest SSTs, the strongest cross-shore temperature gradient and maximum productivity occur in austral winter when seasonally prevailing upwelling favourable winds are weakest. Here, we investigate the seasonal mixed layer heat budget to analyse atmospheric and oceanic causes for heat content variability. By using different satellite and in-situ data, we derive monthly estimates of surface heat fluxes, mean horizontal advection and local heat content change. We calculate the heat budgets for the near coastal and offshore regions separately to explore processes that lead to the observed differences. The results show that the net surface heat flux warms the coastal ocean stronger than further offshore thus acting to damp spatial SST differences. Mean horizontal heat advection is dominated by meridional advection of warm water along the Angolan coast. However, its contribution to the heat budget is small. Ocean turbulence data suggests that the heat flux due to turbulent mixing across the base of the mixed layer is an important cooling term. This turbulent cooling that is strongest in shallow shelf regions is capable of explaining the observed negative cross-shore temperature gradient. The residuum of the mixed layer heat budget and uncertainties of budget terms are discussed.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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  • 9
    Publication Date: 2024-02-14
    Description: In the equatorial Atlantic Ocean, meridional velocity variability exhibits a pronounced peak on intraseasonal timescales whereas zonal velocity dominantly varies on seasonal to interannual timescales. We focus on the intraseasonal meridional velocity variability away from the near-surface layer, its source regions and its pathways into the deep ocean. This deep intraseasonal velocity variability plays a key role in equatorial dynamics as it is an important energy source for the deep equatorial circulation. The results are based on the output of a high-resolution ocean model revealing intraseasonal energy levels along the equator at all depths that are in good agreement with shipboard and moored velocity data. Spectral analyses reveal a pronounced signal of intraseasonal Yanai waves with westward phase velocities and zonal wavelengths longer than 450 km. Different sources and characteristics of these Yanai waves are identified: near the surface between 40°W and 10°W low-baroclinic-mode Yanai waves with periods of around 30 days are exited. These waves have a strong seasonal cycle with a maximum in August. High-frequency Yanai waves (10–20-day period) are excited at the surface east of 10°W. In the region between the North Brazil Current and the Equatorial Undercurrent high-baroclinic-mode Yanai waves with periods between 30 and 40 days are generated. Yanai waves with longer periods (40-80 days) are shed from the Deep Western Boundary Current. The Yanai wave energy is carried along beams east- and downward thus explaining differences in strength, structure and periodicity of the meridional intraseasonal variability in the equatorial Atlantic Ocean.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 10
    Publication Date: 2024-02-12
    Description: The southeastern tropical Atlantic hosts a coastal upwelling system characterized by high biological productivity. Three subregions can be distinguished based on differences in the physical climate: the tropical Angolan and the northern and southern Benguela upwelling systems (tAUS, nBUS, sBUS). The tAUS, which is remotely forced via equatorial and coastal trapped waves, can be characterized as a mixing-driven system, where the wind forcing plays only a secondary role. The nBUS and sBUS are both forced by alongshore winds and offshore cyclonic wind stress curl. While the nBUS is a permanent upwelling system, the sBUS is impacted by the seasonal cycle of alongshore winds. Interannual variability in the region is dominated by Benguela Niños and Niñas that are warm and cold events observed every few years in the tAUS and nBUS. Decadal and multidecadal variations are reported for sea surface temperature and salinity, stratification and subsurface oxygen. Future climate warming is likely associated with a southward shift of the South Atlantic wind system. While the mixing-driven tAUS will most likely be affected by warming and increasing stratification, the nBUS and sBUS will be mostly affected by wind changes with increasing winds in the sBUS and weakening winds in the northern nBUS.
    Type: Book chapter , NonPeerReviewed , info:eu-repo/semantics/bookPart
    Format: text
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