Seasonal Cycle of Sea Surface Salinity in the Angola Upwelling System

Rouault, M.; Ostrowski, Marek; Tomety, Folly Serge; Da‐Allada, C. Y.; Jouanno, Julien

doi:10.1029/2022jc018518

Cited by 11 publications

(28 citation statements)

References 44 publications

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“…Seemingly contradicting to our results, the study of Awo et al (2022) showed that mean horizontal advection is an important term for the seasonal salinity budget. Their analysis shows that freshwater from the Congo River can reach 11°S by meridional advection in February/March and in October/November.…”

Section: Summary and Discussioncontrasting

confidence: 99%

“…However, as the meridional temperature gradient is weak in that region, the mean horizontal advection is not important for the local ML heat budget. Thus, the results of our study do not oppose the results found by Awo et al (2022).…”

Section: Summary and Discussioncontrasting

confidence: 97%

“…1a). This negative crossshore SST gradient as well as the primary productivity peak in austral winter (Tchipalanga et al, 2018;Zeng et al, 2021;Awo et al, 2022). Thus, understanding the drivers of heat content changes in the upper ocean in the tAUS is important for the understanding of productivity.…”

mentioning

confidence: 98%

“…Additionally, it is also of global importance due to the remote impact of the southeast tropical Atlantic on tropical climate (Xu et al 2014). the surface during the passage of the downwelling CTW and surface freshening in February/March and October/November (Kopte et al 2017;Tchipalanga et al, 2018, Awo et al 2022.…”

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confidence: 99%

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Seasonal cycle of sea surface temperature in the tropical Angolan upwelling system

Körner

Brandt

Dengler

2022

Preprint

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Abstract. 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.

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Section: Summary and Discussioncontrasting

confidence: 99%

Section: Summary and Discussioncontrasting

confidence: 97%

mentioning

confidence: 98%

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confidence: 99%

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Seasonal cycle of sea surface temperature in the tropical Angolan upwelling system

Körner

Brandt

Dengler

2022

Preprint

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“…4). In the tAUS during austral winter, maximum productivity is observed at the same time as the lowest SST and the strongest cross-shore temperature gradient are present (Awo et al 2022;Körner et al 2022;Tchipalanga et al 2018). In contrast to other eastern boundary upwelling systems, the seasonality of the productivity in the tAUS cannot be explained by local wind forcing (Ostrowski et al 2009).…”

Section: Tropical Angolan Upwellingmentioning

confidence: 89%

Physical processes in the upwelling regions of the tropical Atlantic

Brandt

Alory²,

Rouault³

et al. 2022

Preprint

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Abstract. In this paper, we review observational and modelling results on the upwelling in the inner tropical Atlantic. We focus on the physical processes that drive the seasonal variability of surface cooling and upward nutrient flux required to explain the seasonality of primary productivity. We separately consider the equatorial upwelling system, the northern coastal upwelling system of the Gulf of Guinea and the tropical Angolan upwelling system. For the equatorial regime, we discuss the 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 concentrated along northern boundary and is driven by both, local and remote forcing. The particular role of the Guinea Current, nonlinearity and the shape of the coastline are emphasized. For the tropical Angolan upwelling, we show that this system is not wind-driven, 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.

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Long-term climatological trends driving the recent warming along the Angolan and Namibian coasts

Tomety,

Illig,

Ostrowski

et al. 2024

Clim Dyn

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The coastal regions off Angola and Namibia are renowned for their highly productive marine ecosystems in the southeast Atlantic. In recent decades, these regions have undergone significant long-term changes. In this study, we investigate the variability of these long-term changes throughout the annual cycle and explore the underlying mechanisms using a 34-year (1982–2015) regional ocean model simulation. The results reveal a clear seasonal dependence of sea surface temperature (SST) trends along the Angolan and Namibian coasts, with alternating positive and negative trends. The long-term warming trend in the Angolan coastal region is mainly explained by a pronounced warming trend in the austral spring and summer (November-January), while the decadal trend off Namibia results from a counterbalance of an austral winter cooling trend and an austral summer warming trend. A heat budget analysis of the mixed-layer temperature variations shows that these changes are explained by a long-term modulation of the coastal currents. The Angolan warming trend is mainly explained by an intensification of the poleward coastal current, which transports more warm equatorial waters towards the Angolan coast. Off Namibia, the warming trend is attributed to a reduction in the northwestward Benguela Current, which advects cooler water from the south to the Namibian coast. These changes in the coastal current are associated with a modulation of the seasonal coastal trapped waves that are remotely-forced along the equatorial waveguide. These long-term changes may have significant implications for local ecosystems and fisheries.

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Seasonal Cycle of Sea Surface Salinity in the Angola Upwelling System

Cited by 11 publications

References 44 publications

Seasonal cycle of sea surface temperature in the tropical Angolan upwelling system

Seasonal cycle of sea surface temperature in the tropical Angolan upwelling system

Physical processes in the upwelling regions of the tropical Atlantic

Long-term climatological trends driving the recent warming along the Angolan and Namibian coasts

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