Coastal trapped waves and tidal mixing control primary production in the tropical Angolan upwelling system

Körner, Mareike; Brandt, Peter; Illig, Serena; Dengler, Marcus; Subramaniam, Ajit; Bachèlery, Marie-Lou; Krahmann, Gerd

doi:10.1126/sciadv.adj6686

Cited by 3 publications

(3 citation statements)

References 70 publications

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“…9b). It's worth noting that Bachèlery et al (2020) and (Körner et al 2024) also emphasized this connection with the equatorial variability, suggesting that changes in the magnitude of equatorially-forced CTW activity could lead to decadal modulation of the Angolan and Namibian coastal variability. This insight implies decadal changes in the equatorial winds triggering the equatorial forcing.…”

Section: Discussionmentioning

confidence: 89%

“…Consequently, the relatively lower temperatures in the NBUS can be attributed to the quasipermanent wind-driven upwelling in the region (Fig. 4b; Veitch et al 2010), while in the TAUS the seasonal variability of the MLT is not driven by the modulation of the surface winds but rather by the passage of equatorially forced annual and semi-annual CTWs (Körner et al 2023(Körner et al , 2024. The analysis of the ML heat budget reveals that the surface forcing contribution (SFORC, see Eq.…”

Section: Climatological Heat Budget Within the Mixed Layermentioning

confidence: 93%

“…River runoffs are not included in the simulation, instead the sea surface salinity is restored to the CARS2009 climatological values. This configuration has been successfully used to study the coastal dynamics off southwest Africa on seasonal (Körner et al 2024) and interannual (Illig et al 2020) timescales. Comparisons with observations can be found in Illig et al (2020).…”

Section: Tropical Atlantic Model Configurationmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 89%

Section: Climatological Heat Budget Within the Mixed Layermentioning

confidence: 93%

Section: Tropical Atlantic Model Configurationmentioning

confidence: 99%

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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

Self Cite

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Influence of the Remote Equatorial Dynamics on the Interannual Variability Along the Northern Coast of the Gulf of Guinea

Illig,

Djakouré,

Mitchodigni

2024

JGR Oceans

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This study explores the oceanic connection between the equatorial dynamics and the coastal variability along the northern coast of the Gulf of Guinea on interannual timescales, based on experiments with a high‐resolution tropical Atlantic Ocean model over 1958–2015. Equatorial Kelvin waves, forced by wind‐stress anomalies in the west‐central equatorial basin, significantly control the interannual fluctuations of the coastal sea‐level and subsurface temperature near the thermocline (>70%), leaving only a marginal role for the local forcing contribution. The dynamical coastal response exhibits a clear propagative nature, with poleward propagations (0.75–1.2 m.s−1) from Cameroon to Liberia. Because the northern coast of the Gulf of Guinea is close to the equatorial waveguide, the coastal variability is influenced by both equatorially‐forced coastal trapped waves and reflected equatorial Rossby waves. Furthermore, remote equatorial forcing explains more of the surface temperature variance for the coastal systems associated with clear upwelling characteristics such as Côte d'Ivoire and Ghana, where subsurface/surface coupling is more efficient. The surface thermal amplitude and timing is shaped by the coastal stratification and circulation and exhibits a marked seasonal modulation, so that the timing of the Sea Surface Temperature (SST) anomalies relative to the dynamical signature lacks consistency, making SST a less reliable variable for tracking coastal propagations in the Gulf of Guinea. Our findings open the possibility of predicting interannual changes in coastal conditions off Côte d'Ivoire and Ghana a few months in advance, to anticipate impacts on fish habitats and resources, and to facilitate proactive measures for sustainable management and conservation efforts.

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Drivers and impact of the 2021 extreme warm event in the tropical Angolan upwelling system

Imbol Koungue,

Brandt,

Prigent

et al. 2024

Sci Rep

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Benguela Niños are extreme warm events that typically occur during the main downwelling season (austral fall) in the tropical Angolan upwelling system when the biological productivity is low. However, the extreme warm event that occurred between April and August 2021 stands out due to its late timing. It occurred and peaked during the main upwelling season in austral winter with sea surface temperature anomalies exceeding 2 °C in the Angola-Benguela area in June 2021. This led to an unprecedented reduction of the net primary production off southern Angola. Both local atmospheric processes and remote influences (via downwelling coastal trapped wave propagations) have contributed to the onset of the extreme warm event in April and its intensification towards the peak phase in June. Moreover, the poleward advection of warm equatorial waters toward the Angola-Benguela area in May 2021 might have contributed to the warming, since the transport of the Angola Current, as estimated from observations, was notably elevated, amounting to 2.1 Sv.

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Coastal trapped waves and tidal mixing control primary production in the tropical Angolan upwelling system

Cited by 3 publications

References 70 publications

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

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

Influence of the Remote Equatorial Dynamics on the Interannual Variability Along the Northern Coast of the Gulf of Guinea

Drivers and impact of the 2021 extreme warm event in the tropical Angolan upwelling system

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