Physical Oceanography on the Angolan continental shelf and Cabinda

Tchipalanga, Pedro Cláver Mota; Ostrowski, Marek; Dengler, Marcus

doi:10.1594/pangaea.886492

Cited by 3 publications

(1 citation statement)

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“…Still, we could conclude from the present analysis that the freshwater input into the ABA related to the strength of the Angola Current is an active local forcing player in the intensification of Benguela Niños. data/gridded/data.gpcp.html); GLORYS12 product is available at (https://data.marine.copernicus.eu/product/ GLOBAL_MULTIYEAR_PHY_001_030/download); CTD profiles from the Nansen Programme are publicly available at https://doi.pangaea.de/10.1594/PANGAEA.886492 (Tchipalanga, Ostrowski, & Dengler, 2018). Flow velocities from mooring data at 11˚S are available at https://doi.pangaea.de/10.1594/PANGAEA.939249 (Hummels et al, 2021).…”

Section: Summary and Discussionmentioning

confidence: 99%

The Influence of Freshwater Input on the Evolution of the 1995 Benguela Niño

Aroucha,

Lübbecke,

Körner

et al. 2024

JGR Oceans

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Benguela Niño events are characterized by strong warm sea surface temperature (SST) anomalies off the Angolan and Namibian coasts. In 1995, the strongest event in the satellite era took place, impacting fish availability in both Angolan and Namibian waters. In this study, we use direct observations, satellite data, and reanalysis products to investigate the impact that the up‐until‐now unnoticed mechanism of freshwater input from Congo River discharge (CRD) and precipitation had on the evolution of the 1995 Benguela Niño. In the onset phase of the event, anomalous rainfall in November/December 1994 at around 6°S, combined with a high CRD, generated a low salinity plume. The plume was advected into the Angola‐Namibia region in the following February/March 1995 by an anomalously strong poleward surface current generated by the relaxation of the southerly winds and shifts in the coastal wind stress curl. The presence of this low surface salinity anomaly of about −2 psu increased ocean stability by generating barrier layers, thereby reducing the turbulent heat loss, since turbulent mixing acted on a weak vertical temperature gradient. A mixed layer heat budget analysis demonstrates that southward advection of Angolan waters drove the warming at the onset, while reduced mixing played the main role at the event's peak. We conclude that a freshwater input contributed to the SST increase in this exceptionally strong event and suggest that this input can influence the SST variability in Angola‐Namibia waters through a combination of high CRD, precipitation, and the presence of a strong poleward surface current.

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Section: Summary and Discussionmentioning

confidence: 99%

The Influence of Freshwater Input on the Evolution of the 1995 Benguela Niño

Aroucha,

Lübbecke,

Körner

et al. 2024

JGR Oceans

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Indian Ocean Dipole intensifies Benguela Niño through Congo River discharge

McPhaden,

Jarugula,

Aroucha

et al. 2024

Commun Earth Environ

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Benguela Niños are episodes of unusual El Niño-like warming in the upwelling zone off the coast of southwest Africa, with consequential impacts on marine ecosystems, coastal fisheries and regional weather. The strongest Benguela Niño in the past 40 years occurred in February–April 1995 with local sea surface temperature anomalies up to 4 °C off the coast of Angola and Namibia. Here, we show that a strong Indian Ocean Dipole in September–November 1994 helped boost the amplitude of the 1995 Benguela Niño through a land bridge involving Congo River discharge. We use atmospheric, oceanic, and hydrological data to demonstrate the sequential linkage between Indian Ocean Dipole development, unusually high rainfall in the Congo River basin, high Congo River discharge, low salinity near the Congo River mouth, and southward advection of this low salinity water into the Benguela upwelling region. The low salinity water isolated the surface mixed layer from the thermocline, which limited vertical mixing with colder subsurface waters and led to enhanced sea surface temperature warming. We also discuss how other Indian Ocean Dipole events may have similarly affected subsequent Benguela Niños and the possibility that Indian Ocean Dipole impacts on Benguela Niños may become more prominent in the future.

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Eastern Boundary Circulation and Hydrography Off Angola: Building Angolan Oceanographic Capacities

Tchipalanga

Dengler

Brandt

et al. 2018

Bulletin of the American Meteorological Society

123

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The eastern boundary region off Angola encompasses a highly productive ecosystem important for the food security of the coastal population. The fish-stock distribution, however, undergoes large variability on intraseasonal, interannual, and longer time scales. These fluctuations are partly associated with large-scale warm anomalies that are often forced remotely from the equatorial Atlantic and propagate southward, reaching the Benguela upwelling off Namibia. Such warm events, named Benguela Niños, occurred in 1995 and in 2011. Here we present results from an underexplored extensive in situ dataset that was analyzed in the framework of a capacity-strengthening effort. The dataset was acquired within the Nansen Programme executed by the Food and Agriculture Organization of the United Nations and funded by the Norwegian government. It consists of hydrographic and velocity data from the Angolan continental margin acquired biannually during the main downwelling and upwelling seasons over more than 20 years. The mean seasonal changes of the Angola Current from 6° to 17°S are presented. During austral summer the southward Angola Current is concentrated in the upper 150 m. It strengthens from north to south, reaching a velocity maximum just north of the Angola Benguela Front. During austral winter the Angola Current is weaker, but deeper reaching. While the southward strengthening of the Angola Current can be related to the wind forcing, its seasonal variability is most likely explained by coastally trapped waves. On interannual time scales, the hydrographic data reveal remarkable variability in subsurface upper-ocean heat content. In particular, the 2011 Benguela Niño was preceded by a strong subsurface warming of about 2 years’ duration.

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Physical Oceanography on the Angolan continental shelf and Cabinda

Cited by 3 publications

References 0 publications

The Influence of Freshwater Input on the Evolution of the 1995 Benguela Niño

The Influence of Freshwater Input on the Evolution of the 1995 Benguela Niño

Indian Ocean Dipole intensifies Benguela Niño through Congo River discharge

Eastern Boundary Circulation and Hydrography Off Angola: Building Angolan Oceanographic Capacities

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