The seasonal cycle of sea surface salinity (SSS) along the Angolan coast is investigated using observations and a regional ocean model. The model reproduces the main characteristic of the seasonal cycle of SSS along the Angolan coast, such as the freshwater discharge signature off the Congo River plume and the low‐salinity observed in February/March and October/November along the Angolan coast. The model also reproduces the two maxima of salinity in June/July and December/January. The analysis of the model salt budget reveals that the semi‐annual cycle of SSS is controlled by the meridional advection of surface water, the vertical advection of subsurface water, and the mixing at the base of the mixed layer. The meridional advection is controlled by the Angola Current which brings low‐salinity water from offshore region of the Congolese coast toward the south Angolan coast in February/March and October/November. The vertical advection contribution is modulated by the vertical stratification of salinity and not by vertical velocities which peak during the main Angolan upwelling season. The vertical stratification is due to the low‐salinity intrusion at the Angolan coast that creates a strong vertical salinity gradient with low‐salinity at the surface and high salinity at the subsurface.

This paper assesses the morphological storm-event impact, seasonal cycles, trends of wave forcing, and beach’s response at the coastal area of Grand Popo, Benin. Three and a half years’ worth of data were collected from 2013 to 2016, using a video system calibrated with field data collected during a 10 day experiment. A comparison was carried out with Wavewatch III IOWAGA wave hindcast data. The along-shore-averaged shoreline position exhibited a seasonal pattern, which was related more to the average wave height than the average storm intensity. Storms occur in austral winter (June, July, August, and September). Based on 12 storms, the results revealed that the average storm duration was 1.6 days, with a mean erosion of 3.1 m. The average post-storm beach recovery duration was 15 days, and the average recovery rate was 0.4 m/day. The impact of storms was more or less amplified depending on the eroding and accreting periods of the wave climate. There was an inter-annual eroding trend of about −1.6 m/year, but the causes of this trend could not be explained.

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.

As a result of the high volume of maritime traffic along the coasts of Namibia and western South Africa, mariners recorded numerous in-situ wind observations since early times. Many of these historical data are currently available through the International Comprehensive Ocean-Atmosphere Data Set (ICOADS). Here, we make use of these historical data to develop an instrumental index for the characterization of the upwelling-favorable winds over the southern Benguela Upwelling System from 1833 to 2014. Our results suggest that upwelling in this region has increased since the mid-1980s, in good agreement with previous research. However, when the entire period is considered, our index does not evidence a long-term trend but a multidecadal variability with an oscillation period between 20 and 30 years. We found a significant influence of ENSO exerted through the modulation of the position of the South Atlantic high-pressure system. However, this teleconnection may be highly non-stationary.

Field measurements of longshore sediment transport have been performed in the surf zone along Denu Beach, located in the Volta Region of Ghana, West Africa. This study consisted of measuring sediment transport rates by the deployment of modified versions of Kraus streamer traps on a cross-shore distance, which was about half the average surf zone width. In addition to the measured transport rates, data on waves, longshore currents, and other morphological parameters were collected with simple and low-cost instrumentation. In total, about 22 datasets were obtained through several days of data collection spanning a period of 5 months. Mathematical formulae proposed by CERC (1984), Kamphuis (1991), and the new van Rijn (2014) were used to compute theoretical transports for the entire surf zone, which were validated by measured data. Applying the CERC equation with a K-value of 0.39, the theoretical transports were about one order of magnitude higher than the measured rates. The rates computed by the Kamphuis formula were slightly higher than those yielded by the van Rijn equation. They produced values that were, on average, about 3.5 and 2.9 times higher than the measured rates, respectively. This study then confirmed the capabilities of both the Kamphuis and van Rijn equations to provide closer estimates of longshore sediment transport on Denu Beach. It especially sheds light on the new van Rijn formula, which has not been used extensively in LST quantification across the world. We, therefore, concluded that both the Kamphuis and van Rijn equations could be particularly useful to local engineers in the prediction of LST prior to the design of coastal protection structures. Further long-term studies employing available cutting-edge technologies were also recommended to provide more information on longshore transport not only in Ghana but also in the entire Gulf of Guinea and for the establishment of a reliable sediment budget for the country and the entire region.

The Angola-Benguela upwelling system (ABUS), a vital marine ecosystem in the southeast Atlantic, supports rich fisheries and provides food and economic security for coastal populations. While several studies have shown that global warming is altering sea surface temperature (SST) variability and upwelling dynamics across its subsystems, there is a dearth of knowledge about the extent to which human intervention, like Stratospheric Aerosol Injection (SAI), could mitigate the influence of global warming on ABUS. This study investigates projected physical changes in the ABUS under a mid-range emission scenario (SSP2-4.5) and evaluates the potential of SAI to mitigate these impacts. We focus on the three major upwelling subsystems: the south Benguela (sBUS), north Benguela (nBUS) and Angola Upwelling System (AUS). Using earth system climate model simulations, we analyse changes in two key physical parameters critical for ecosystem development: ocean temperature and upward motion. Under the SSP2-4.5 scenario, the southeast tropical Atlantic, including upwelling regions, is projected to warm by up to 1.4 °C. This warming is primarily driven by enhanced downward longwave radiation and modulated by cloud radiative effects and ocean circulation. Despite this warming, the upwelling dynamics remain largely unaffected during the main upwelling seasons: December to February (DJF) in sBUS and June to August (JJA) in nBUS and AUS. In contrast, during the secondary upwelling seasons (JJA in the sBUS and DJF in the nBUS and AUS), the upward motion intensifies by ~30% in the AUS and by 10 – 20% in the sBUS, while a weakening is projected in the nBUS. Under the SAI scenario, most of the climate change (CC)-induced warming is offset, with up to 90% of the temperature increase mitigated, particularly within the upper 150 m. The thermocline shoals by up to 80% of the CC-induced deepening. Additionally, the SAI scenario reverses up to 90% the CC-driven intensification of the upward motion during secondary upwelling seasons across all three upwelling subsystems. However, SAI fails to restore large-scale offshore ocean circulation in the broader ABUS region. Overall, these results highlight the spatially uneven effectiveness of SAI in moderating regional ocean-climate feedback within the ABUS.