The eastern boundary circulation off the coast of Angola has been described only sparsely to date, although it is a key element in the understanding of the highly productive tropical marine ecosystem off Angola. Here, we report for the first time direct velocity observations of the Angola Current (AC) at ∼11°S collected between July 2013 and October 2015 in the depth range from 45 to 450 m. The measurements reveal an alongshore flow that is dominated by intraseasonal to seasonal variability with periodically alternating southward and northward velocities in the range of ±40 cm/s. During the observation period, a weak southward mean flow of 5–8 cm/s at 50 m depth is observed, with the southward current extending down to about 200 m depth. Corresponding mean southward transport of the AC is estimated to be 0.32 ± 0.046 Sv. An extensive set of hydrographic measurements is used to investigate the thermal structure and seasonality in the hydrography of the eastern boundary circulation. Within the depth range of the AC, the superposition of annual and semiannual harmonics explains a significant part of the total variability, although salinity in the near surface layer appears to be also impacted by year‐to‐year variability and/or short‐term freshening events. In the central water layer, temperature and salinity on isopycnals vary only weakly on seasonal to annual time scales. The available data set is further used to evaluate different reanalysis products particularly emphasizing the ocean's role in coupled climate model SST biases in the Eastern Tropical Atlantic.

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.

The NansClim project (2010–2013) represented a regional collaboration to assess the effects of climate on Benguela dynamics. Based on in situ (since the 1960s in Namibia and South Africa and 1985 in Angola) and satellite (since the 1980s) observations, the project focussed on four subsystems, namely the Angola subtropical, northern Benguela upwelling, southern Benguela upwelling and Agulhas Bank. This contribution summarizes the findings for selected key questions, ranging from changes in the physico‐chemical habitats, plankton, pelagic and demersal fish communities, to cross‐cutting evaluation at subsystem and regional scales. The results underline the overriding importance to of considering the combined effects of climate and fishing as drivers of the dynamics of the ecosystem components. Each subsystem currently continues to function largely as a separate entity as described in earlier reviews. However, some changes have been observed across several subsystems, e.g., a coherent shift from one relatively stable period to another occurred in the northern and southern Benguela in the mid‐1990s. Future climate change could weaken the boundaries between the four subystems. The findings underline the need for continued regional research collaboration and regional surveys focussed at ecosystem, rather than resource, assessment. Our conclusions include implications for ecosystem‐based fisheries management, and recommendations for future regional research.

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