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For the first time, the temperature transport of the Agulhas Current is quantified in a time series. Over a 25-month mooring deployment at 34°S, seven tall moorings were instrumented to measure current velocity, temperature, and salinity. Current- and pressure-recording inverted echosounders were used to extend geostrophic velocity, temperature, and salinity records to 300 km offshore. In the mean, the current transports 3.8 PW of heat southward relative to 0°C: −76 Sv (1 Sv ≡ 106 m3 s−1) at a transport-weighted temperature of 12.3°C. A 0.9-PW standard deviation in temperature transport is due to variability in both volume transport and the temperature field. Meandering of the current core dominates variability in the temperature field by warming temperatures offshore and cooling temperatures near the coast. However, meandering has a limited impact on the temperature transport, which varies more closely with a deepening and broadening of the current associated with an inshore isotherm shoaling and an offshore isotherm deepening. Stronger southward temperature transports correspond to a deeper current transporting more volume, yet at a cooler transport-weighted temperature. Seasonality is not observed in the temperature transport time series, possibly because of the offsetting effects of cooler temperatures during times of seasonally stronger volume transports. Although volume transport and temperature transport are highly correlated, the large variability in transport-weighted temperature means that using volume transport alone to infer temperature transport results in an error that could be as large as 24% of the southern Indian Ocean heat transport.

The Agulhas Current, like all western boundary currents, transports salt from the subtropics toward the poles and, on average, acts as a barrier to exchange between the open ocean and continental seas. Uniquely, the Agulhas jet also feeds a leakage of relatively salty waters from the Indian Ocean into the Atlantic Ocean. Despite its significance, the signals and drivers of water mass variability within the Agulhas Current are not well known. To bridge this gap, we use 26 months of moored observations to determine how and why salinity—a water mass tracer—varies across the Agulhas Current. We find that salinity variability is driven by both shifting (i.e., changes in location) and pulsing (i.e., changes in strength) of the current. Shifting of the current causes heave and diapycnal mixing of subtropical, central, and intermediate waters. Diapycnal mixing between central and intermediate waters explains most of the variability, creating salinity anomalies between −0.4 and +0.1 psu. Pulsing of the current drives heave and, to a lesser extent, along-isopycnal mixing within the halocline. This cross-stream mixing results in salinity anomalies of up to 0.3 psu. The mean and standard deviation of Agulhas Current volume and salt transports are −76 and 22 Sv (1 Sv ≡ 106 m3 s−1) and −2650 and 770 Sv psu. Transport-weighted salinity has a standard deviation of 0.05 psu. We estimate that O(1013) kg yr−1 of the salt transported southwestward leaks into the fresher Atlantic Ocean. On the basis of our observations, the variability of the Agulhas Current could alter this salt leakage by an order of magnitude.

The zoogeography of marine Bryozoa around South Africa was investigated using published distribution records, museum catalogues, and an examination of previously unworked bryozoan material in (most...

Agulhas leakage, the warm and salty inflow of Indian Ocean water into the Atlantic Ocean, is of importance for the climate-relevant Atlantic Meridional Overturning Circulation. South of Africa, the eastward turning Agulhas Current sheds Agulhas rings, cyclones and filaments of order 100 km that carry the Indian Ocean water into the Cape Basin and further into the Atlantic. Here, we show that the resolution of submesoscale flows of order 10 km in an ocean model leads to 40 % more Agulhas leakage and more realistic Cape Basin water-masses compared to a parallel non-submesoscale resolving simulation. Moreover, we show that submesoscale flows strengthen shear-edge eddies and in consequence lee cyclones at the northern edge of the Agulhas Current, as well as the leakage pathway in the region of the filaments that takes place outside of mesoscale eddies. This indicates that the increase in leakage can be attributed to stronger Agulhas filaments, when submesoscale flows are resolved. Leakage of warm, salty waters from the Indian Ocean into the Atlantic increases by up to 40 % in high-resolution numerical ocean model simulations, suggesting that low-resolution models underestimate this key part of the global meridional overturning circulation.

Researchers turn to the shipping industry for data on ocean surface currents.

Based on the high-resolution Eulerian fields of an ocean general circulation model simulation, the heat contribution of the Indonesian throughflow (ITF) to the Indian Ocean is estimated by Lagrangian tracing method. The heat transport of each particle of ITF waters is calculated by tracing temperature change along the trajectory until the particle exits the Indian Ocean. The simulation reveals that the ITF waters flow westward and branch near Madagascar, further showing the ITF waters are redistributed in both northern and southern Indian Ocean. Heat budget analysis indicates that the ITF waters gain 0.41 PW (Petawatts, 1015 W) in the northern Indian Ocean and lose 0.56 PW in the southern Indian Ocean, respectively. As a result, the ITF waters warm the whole Indian Ocean basin with only 0.15 PW, which shows an “insignificant” role of ITF on the Indian Ocean because of the heat exchange compensation between northern and southern Indian Ocean. Furthermore, the tracing pathways show that the ITF waters mainly flow out the Indian Ocean at both sides of the basin via Agulhas Current and Leeuwin Current. About 89% of the ITF waters leave along western boundary and the rest 11% along eastern boundary. Compared to seeding section, 0.10 PW and 0.05 PW are released to the Indian Ocean, respectively.

The discrimination of sediment provenance from specific source regions is a crucial prerequisite for the paleoclimatic interpretation of terrigenous sediment archives. The terrigenous material in sediments on the Delagoa Bight near Maputo, Mozambique, has several potential source areas including the Limpopo, Incomati, Matola, and Lusutfu river catchments. While the last three represent a coastal region bordered to the west by the Drakensberg mountains, the Limpopo catchment is much larger and reaches farther into the center of the continent. Due to local current patterns, the sedimentation in the Delagoa Bight is very complex. This may be the reason why previous studies in this area interpreted the origin of sediment bodies only on the basis of seismic profiles. Analytical investigations to the question where which material was/is deposited in the Delagoa Bight, especially the suspension load from the Limpopo River, do not exist. In this study, end-members for the four river catchments were determined based on a selection of aluminium-normalized trace element concentrations in river sediment samples. Relative end-member contribution to core top samples from the shelf, partitioned using a constrained least squares model, and age data of marine surface sediments, indicate a very effective eastward sediment drift, caused by local cyclonic circulation. This strong lee circulation (the Delagoa Bight Eddy) may have meant that hardly any material has been deposited in the eastern and central parts of the bight for ~1000 years. In addition, our results confirm previous studies showing that the majority of Limpopo sediments are dumped onto the eastern flank of the Inharrime Terrace from where material is probably drifted further south under the influence of the Agulhas Current.

From the southwestern termination of the Agulhas current, anticyclonic eddies are emitted and drift across the South Atlantic Ocean. This study is based on a FORSA (Following Ocean Rings in the South Atlantic) oceanographic cruise, from Cape Town (South AFRica) to Arraial do Cabo (Brazil) in June 2015, during which three eddies of different ages (E1, 7 months; E3, 11 months; E5, 24 months) from the Agulhas current were sampled for microplankton identification and determination of functional traits. The stations where sampling occurred at each eddy included a control outside the eddy and three stations inside the eddy—border, midway (between the border and center), and center (identified through satellite images of sea level anomaly—SLA). Functional traits were determined based on microscopic observations and consultation of the literature. An evident decay in the Agulhas eddies toward the west was observed, and each eddy proved to be different. E1 represented a younger and more robust structure. At the same time, the other eddies, E3 and E5, were more alike with similar physical, chemical, and ecological characteristics and almost the same indices values of functional diversity, demonstrating that although their species compositions were different, the strategies used by the species were the same. The most crucial ecological trait for microplankton was nutrition mode. The microplankton contained mainly mixotrophic dinoflagellates and cyanobacteria adapted to oligotrophic conditions. The functional strategy of microplankton did not differ among the eddies and stations, with mixotrophy being the most striking trait. Therefore, the older eddies’ microplankton community fits the neutrality theory, whereby species perform similar ecological functions, and the younger eddy fits in the niche complementarity. Even with the species composition being different in each eddy and/or within the same eddy, the functional strategy was the same, with scarce resources and species selected that best use any source of nutrients or use evolutionary advantages to live in an oligotrophic environment.

Advances in the understanding and modelling of surface currents have revealed the importance of internal waves, mesoscale and submesoscale features. Indeed all these features should have a large influence on wind waves and in particular on wave heights. Still, the quantitative impact of currents on waves is not well known due to the complexity of the random wave fields and currents that are found in the ocean, and the lack of observations of both currents and waves at scales shorter than 150km. Here we compare novel satellite altimetry data and state of the art phase‐averaged numerical wave models forced both by wind and currents. Currents used are taken from the oceanic model CROCO, run at high resolution. The influence of current field resolution is investigated by applying Gaussian filters of different width to that same high resolution current field. We find that a numerical wave model that uses currents with resolutions of ∼30km or less and a directional resolution of 7.5°, can provide accurate representations of the significant wave height gradients found in the Agulhas current. Using smoother current fields such as derived from altimeters measurements alone, coarse directional spectral resolution or larger directional spread of the wave model, generally underestimates gradients and extreme wave heights. Hence, satellite altimetry provides high resolution wave height with a gradient magnitude that is highly sensitive to underlying surface current gradients, at resolutions that may not be resolved by today's altimeters measurements. This is demonstrated here for relatively steady currents averaged over 3 years. Plain Language Summary Mariners have learned to be wary of severe sea states, especially in strong currents like the Agulhas that flows along the South African coast, where wave heights in the current can be several meters taller than in the surrounding waters. Mariners have also learned to spot currents by watching the water ahead of them. Here we use satellite measurements of wave heights and a numerical wave model to understand the parameters that control the spatial variation of wave heights across currents. We particularly question the necessary current magnitude and gradient that are required to explain observed wave height gradients. Modeled gradients fade for smooth surface currents like surface currents estimated from satellite measurements of sea level or typical global ocean circulation models. Also, numerical experiments have shown that when incident waves have a narrow range of directions, wave height gradients are sharper. A good wave model should thus resolve both the current features, with a spatial resolution better than 30 km, and the range of wave directions, typically using 48 directions or more. Such a good model can then be used to evaluate the quality of modeled ocean currents by matching the modeled strength of wave height gradients with measurements.

The interocean transfer of thermocline water between the Indian and the Atlantic Oceans known as ‘Agulhas leakage’ is of global significance as it influences the Atlantic Meridional Overturning Circulation (AMOC) on different time scales. Variability in the Agulhas Current regime is key in shaping hydroclimate on the adjacent coastal areas of the African continent today as well as during past climates. However, the lack of long, continuous records from the proximal Agulhas Current region dating beyond the last glacial cycle prevents elucidation of its role in regional and wider global climate changes. This is the first continuous record of hydrographic variability (SST; δ18Osw) from the Agulhas Current core region spanning the past 270,000 years. The data set is analytical sound and provides a solid age model. As such, it can be used by paleoclimate scientists, archaeologists, and climate modelers to evaluate, for example, linkages between the Agulhas Current system and AMOC dynamics, as well as connections between ocean heat transport and Southern African climate change in the past and its impact on human evolution., Measurement(s) temperature of sea surface • salinity Technology Type(s) gas chromatography of ketone fractions • gas chromatography • Magnesium-to-calcium ratio measurements of planktonic foraminifera • stable isotope analysis • glycerol dialkyl glycerol tetraether (GDGT) analysis • computational modeling technique Factor Type(s) temporal measurement Sample Characteristic - Environment hydroclimate • ocean Sample Characteristic - Location Agulhas Current Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.13019678

The rate of change in the marine environment over the eastern Agulhas Bank along the south coast of South Africa (32–37∘ S, 20–30∘ E) is studied using reanalysis observations for 1900–2015 and coupled ensemble model projections for 1980–2100. Outcomes are influenced by resolution and time span: ∼ 1∘ datasets covering the whole period capture large-scale changes, while ∼ 0.5∘ datasets in the satellite era better distinguish the cross-shelf gradients. Although sea surface temperatures offshore are warming rapidly (0.05 ∘C yr−1 since 1980), a trend toward easterly winds and a locally stronger Agulhas Current have intensified nearshore upwelling (−0.03 ∘C yr−1). The subtropical ridge is gradually moving poleward, leading to a drier climate.

Place: Oxford Publisher: Pergamon-Elsevier Science Ltd WOS:000556810400013; This work is part of the MADRidge Project special issue which aims to describe pelagic ecosystems in the vicinity of three prominent shallow seamounts in the South West Indian Ocean: one here named MAD-Ridge (240 m below the surface) plus Walters Shoal (18 m) on the Madagascar Ridge, and La Perouse (60 m) on the abyssal plain east of Madagascar. The three span latitudes 20 degrees S and 33 degrees S, some 1500 km. The study provides the background oceanography for the once-off, multidisciplinary snapshot cruise studies around the seamounts. As life on seamounts is determined by factors such as summit depth, proximity to the light layers of the ocean, and the ambient circulation, a first description of regional spatial-field climatologies (16-22 years) and monthly along-ridge gradients of surface wind (driving force), water column properties of sea surface temperature, mixed layer depth, chlorophyll-a and eddy kinetic energy, plus ocean currents is provided. Being relevant to many applications in the study domain, these properties in particular reveal contrasting environments along the Madagascar Ridge and between the three seamounts that should drive biological differences. Relative to the other two seamounts, MAD-Ridge is in the more extreme situation, being at the end of the East Madagascar Current, where it experiences sturdy, albeit variable, currents and the frequent passing of mesoscale eddies.

Place: Oxford Publisher: Pergamon-Elsevier Science Ltd WOS:000556810400006; The composition and spatial variability of ichthyoplankton assemblages were investigated at three shallow seamounts between latitudes 19 degrees S and 33 degrees S in the South West Indian Ocean (SWIO) - La Perouse (60 m), an unnamed pinnacle south of Madagascar, referred to hereafter as MAD-Ridge (240 m), and the Walters Shoal seamount (18 m). In all, 299 larvae (23 families, 54 species) were present at La Perouse, 964 larvae (58 families and 127 species) at MAD-Ridge, and 129 larvae (9 families, 24 species) at the Walters Shoal. Larvae of mesopelagic fish in the families Myctophidae and Gonostomatidae were the most dominant at all three seamounts. All developmental stages were present at each seamount, suggesting the larval pelagic phase of certain species occurs at the seamounts. A 'seamount effect' was detected only at MAD-Ridge where larval fish densities were significantly higher at summit stations. Overall, MAD-Ridge had much higher densities of fish larvae (157.0 larvae 100 m(-3)) than La Perouse (31.1 larvae 100 m(-3)) and the Walters Shoal (9.6 larvae 100 m(-3)). Our study demonstrates that ichthyoplankton communities at shallow seamounts in the SWIO are more influenced by their location relative to a landmass, and to oceanographic features such as currents, mesoscale eddies and water masses than the seamount latitude and topography itself.

Microplastics (MPs) existence, identification and source were investigated by studying a total of 2539 particles in 349 sediment samples from nine different tourist beaches [(Sodwana & Richard Bays; Ballito, Mtunzini, Tugela, Zinkwazi, Ballito (north & south) and Durban north & south)] of southeastern coast of South Africa. They are more abundant in the beaches of the Durban city, followed by the Sodwana & Richards Bays, Ballito and Mtunzini. The black particles prevailed over the blue, white, pink, brown, red and green MPs. Supremacy of MPs in the Durban city is mainly due to the longshore coastal Agulhas current in the South eastern side of African coast aiding the degradation of primary plastics coming both from continent and sea. SEM images provided the evidences of weathering/degrading process through grooves, cracks, deep fissures, sharp edges and layered degradation showing signs of oxidation due to long term exposure in the coastal environment. EDS results suggested presence of elements (i.e. C, -O, Si, Al, Fe, Ca, Mg, Na, K, S, Ti, Cu and Zn introduced during the production of plastics as additives. FTIR spectral matches identified from all samples infer polypropylene (PP) (62%), rayon (RY) (17.2%), polycarbonate (PC) (29.8%), nylon (NY) (18.92%), polyester (PES) (31.2%), polyacrylonitrile (PAN) (11.21%) and polystyrene (PS) as well as low (28.9%) & high (36.1%) polyethylene terephthalate (PET). Higher abundance of MPs in the beaches of South Africa in comparison with studies around the world emphasizes the need of dispersal monitoring and use of plastic materials/polymers.

A complex and highly dynamical ocean region, the Agulhas Current System plays an important role in the transfer of energy, nutrients and organic material from the Indian to the Atlantic Ocean. Its dynamics are not only important locally, but affect the global ocean-atmosphere system. In working towards improved ocean reanalysis and forecasting capabilities, it is important that numerical models simulate mesoscale variability accurately—especially given the scarcity of coherent observational platforms in the region. Data assimilation makes use of scarce observations, a dynamical model and their respective error statistics to estimate a new, improved model state that minimises the distance to the observations whilst preserving dynamical consistency. Qualitatively, it is unclear whether this minimisation directly translates to an improved representation of mesoscale dynamics. In this study, the impact of assimilating along-track sea-level anomaly (SLA) data into a regional Hybrid Coordinate Ocean Model (HYCOM) is investigated with regard to the simulation of mesoscale eddy characteristics. We use an eddy-tracking algorithm and compare the derived eddy characteristics of an assimilated (ASSIM) and an unassimilated (FREE) simulation experiment in HYCOM with gridded satellite altimetry-derived SLA data. Using an eddy tracking algorithm, we are able to quantitatively evaluate whether assimilation updates the model state estimate such that simulated mesoscale eddy characteristics are improved. Additionally, the analysis revealed limitations in the dynamical model and the data assimilation scheme, as well as artefacts introduced from the eddy tracking scheme. With some exceptions, ASSIM yields improvements over FREE in eddy density distribution and dynamics. Notably, it was found that FREE significantly underestimates the number of eddies south of Madagascar compared to gridded altimetry, with only slight improvements introduced through assimilation, highlighting the models’ limitation in sustaining mesoscale activity in this region. Interestingly, it was found that the threshold for the maximum eddy propagation velocity in the eddy detection scheme is often exceeded when data assimilation relocates an eddy, causing the algorithm to interpret the discontinuity as eddy genesis, which directly influences the eddy count, lifetime and propagation velocity, and indirectly influences other metrics such as non-linearity. Finally, the analysis allowed us to separate eddy kinetic energy into contributions from detected mesoscale eddies and meandering currents, revealing that the assimilation of SLA has a greater impact on mesoscale eddies than on meandering currents.

The southern Cape coastal region is important for understanding both the behavioural history of modern humans, and regional and global climate dynamics, because it boasts a long archaeological record and occupies a key geographical location near the intersection of two major oceans. The western boundary Agulhas Current, implicated in global heat exchange dynamics, is an important modulator of southern African climates and yet we understand its past behaviour only broadly as the Current itself scours the coastal shelf and marine sediment core records necessarily provide little detail. Numerous archaeological sites from both the late Pleistocene and Holocene provide the opportunity for reconstruction of near-shore seasonal SST records, which respond both to localized wind-driven upwellings and Agulhas temperature shifts, corresponding in turn with terrestrial precipitation trends in the near-coastal and summer rainfall regions. Here we present a record of seasonal SSTs extending over MIS5, MIS4, and the Holocene, from serial δ18O measurements of a single gastropod species, Turbo sarmaticus. The results show that mean SST shifts accord well with global SST trends, although they are larger than those recorded in the Agulhas Current from coarser- scale marine sediment records. Comparison with a record of Antarctic sea-ice suggests that annual SST amplitude responds to Antarctic sea-ice extent, reflecting the positioning of the regional wind systems that drive upwelling dynamics along the coast. Thus, near-shore SST seasonality reflects the relative dominance of the westerly and easterly wind systems. These data provide a new climate archive for an important but understudied climate system.

We examine the mean pathways, transit timescales, and transformation of waters flowing from the Pacific and the marginal seas through the Indian Ocean (IO) on their way toward the South Atlantic within a high-resolution ocean/sea-ice model. The model fields are analyzed from a Lagrangian perspective where water volumes are tracked as they enter the IO. The IO contributes 12.6 Sv to Agulhas leakage, which within the model is 14.1 ± 2.2 Sv, the rest originates from the South Atlantic. The Indonesian Through-flow constitutes about half of the IO contribution, is surface bound, cools and salinificates as it leaves the basin within 10–30 years. Waters entering the IO south of Australia are at intermediate depths and maintain their temperature-salinity properties as they exit the basin within 15–35 years. Of these waters, the contribution from Tasman leakage is 1.4 Sv. The rest stem from recirculation from the frontal regions of the Southern Ocean. The marginal seas export 1.0 Sv into the Atlantic within 15–40 years, and the waters cool and freshen on-route. However, the model's simulation of waters from the Gulfs of Aden and Oman are too light and hence overly influenced by upper ocean circulations. In the Cape Basin, Agulhas leakage is well mixed. On-route, temperature-salinity transformations occur predominantly in the Arabian Sea and within the greater Agulhas Current region. Overall, the IO exports at least 7.9 Sv from the Pacific to the Atlantic, thereby quantifying the strength of the upper cell of the global conveyor belt.

Gliders were deployed for the first time in the Agulhas Current region to investigate processes of interactions between western boundary currents and shelf waters. Continuous observations from the gliders in water depths of 100–1000 m and over a period of 1 month provide the first high-resolution observations of the Agulhas Current's inshore front. The observations collected in a nonmeandering Agulhas Current show the presence of submesoscale cyclonic eddies, generated at the inshore boundary of the Agulhas Current. The submesoscale cyclones are often associated with warm water plumes, which extend from their western edge and exhibit strong northeastward currents. These features are a result of shear instabilities and extract their energy from the mean Agulhas Current jet.

Strong upwelling events inshore of the Agulhas Current close to 33.5°S are investigated. These events are important to the exchange of shelf and slope waters, potentially enhancing primary productivity and advecting larvae offshore. Using hydrographic observations, this study shows that a wind-driven upwelling event and a current-driven upwelling event can each advect central waters more than 130 m upward, resulting in a maximum 9°C cooling at 50-m depth over the continental shelf and surface cooling greater than 4°C. The authors use satellite data to assess the frequency and forcing mechanisms of similar cold events from January 2003 through December 2011, defining cold events as days when the sea surface temperature (SST) anomaly is significantly correlated with a local current or wind forcing. The authors identify 47 events with an average length of 2.2 days and SST anomaly of −1.6°C, corresponding to an average 13 days of surface cold events along the Agulhas Current front per year. This study uses combined EOF analysis to characterize these cold events based on four highly correlated forcing mechanisms: alongshore wind speed, wind stress curl, current meandering, and current speed over the slope. The authors find that meanders act in combination with upwelling-favorable winds to force the strongest cold events, while upwelling-favorable winds alone, possibly primed by Ekman veering, force weaker cold events. Most significantly, it is found that the frontal curvature of warm Agulhas Current meanders couples with the atmosphere to drive local wind stress curl anomalies that reinforce upwelling.

This study addresses the dynamics of the Agulhas inshore front in the submesoscale range upstream of 26 degrees E. Submesoscale frontal eddies are observed in the vicinity of Port Elizabeth (26 degrees E) from satellite images and in observations collected from underwater gliders. Using a submesoscale-resolving numerical model (dx similar to 0.75 km), we are able to simulate similar submesoscale eddies. Barotropic instability is confirmed as the generation mechanism by a one-dimensional linear stability analysis and an eddy kinetic energy budget. Kinetic energy is transferred from the mean flow to the eddies through the mean horizontal shear, which is a signature of barotropic instability. When the Agulhas Current is in a nonmeandering state, submesoscale eddy generation is a recurrent process which locally drives the front's variability. Along the front, the spatial variability of barotropic instability is shaped by the background strain. A large strain aligned with the frontal axis intensifies the frontal shear upstream of 28 degrees E while a weakening of the strain allows for barotropic instability to be triggered downstream. Although an intermittent process, the barotropic instability shows a dominant period of variability comparable with the variability of the Agulhas Current and Undercurrent.

The westerlies and trade winds over the South Atlantic and Indian Ocean are important drivers of the regional oceanography around Southern Africa, including features such as the Agulhas current, the Agulhas leakage and the Benguela upwelling. The Agulhas leakage is the transport of warm and saline water from the Indian Ocean into the South Atlantic. The leakage is stronger during intensified westerlies and probably also when the wind systems are shifted poleward. Here we analyzed the wind stress of different observational and modelled atmospheric data sets (covering the last two millennia, the recent decades and the 21st century) with regard to the intensity and position of the south-easterly trades and the westerlies. The analysis reveals that variations of both wind systems go hand in hand. A poleward shift and intensification of westerlies and trades took place during the recent decades. Furthermore, the upwelling in South Benguela slightly intensified and the characteristics of the water masses fed into the upwelling region changed with a poleward shift of the trades. Projections for strength and position of the westerlies in the 21st century depend on assumed CO2 emissions. In the strongest emission scenario a further southward displacement will occur, whereas a northward shift is modelled in the weakest emission scenario, possibly due to the dominating driving effect of ozone recovery. Thus, the Agulhas leakage has intensified during the last decades and is projected to increase if greenhouse gas emission are not reduced. This will have a small impact on Benguela upwelling strength, but will have consequences for water mass characteristics in the upwelling region. An increased contribution of Agulhas water to the upwelling feed water masses will import more preformed nutrients and oxygen into the upwelling region.

The Agulhas Current is a critical component of global ocean circulation and has been observed to respond to El Niño Southern Oscillation (ENSO) events via its temperature and salinity signatures. In this research, we use sea surface salinity (SSS) from the National Aeronautics and Space Administration’s (NASA) Soil Moisture Active Passive (SMAP) satellite, sea surface temperature (SST) observations from the Canadian Meteorological Centre (CMC), sea surface height (SSH) anomalies from altimetry, and the Oceanic Niño Index to study the SMAP satellite time period of April 2015 through March 2020 (to observe full years of study). We see warming and high salinities after El Niño, cooling and fresher surface waters after La Niña, and a stronger temperature response than that of salinity. About one year after the 2015 El Niño, there is a warming of the entire region except at the Antarctic Circumpolar Current. About two years after the event, there is an increase in salinity along the eastern coast of Africa and in the Agulhas Current region. About two years after the 2016 and 2018 La Niñas, there is a cooling south of Madagascar and in the Agulhas Current. There are no major changes in salinity seen in the Agulhas Current, but there is a highly saline mass of water west of the Indonesian Throughflow about two years after the La Niña events. Wavelet coherence analysis finds that SSS and ENSO are most strongly correlated a year after the 2015 El Niño and two years after the 2016 La Niña.

The semi-permanent Durban Eddy is a mesoscale, lee-trapped, cold-core cyclonic circulation that occurs off the east coast of South Africa between Durban in the north and Sezela, some 70 km to the south. When present, strong north-eastward countercurrents reaching 100 cm s–1 are found inshore. It is hypothesised that the cyclone is driven by the strong south-westward flowing Agulhas Current offshore of the regressing shelf edge near Durban. Analysis of ADCP data and satellite imagery shows the eddy to be present off Durban approximately 55% of the time, with an average lifespan of 8.6 days, and inter-eddy periods of 4 to 8 days. After spin-up the eddy breaks loose from its lee position and propagates downstream on the inshore boundary of the Agulhas Current. The eddy is highly variable in occurrence, strength and downstream propagation speeds. There is no detectable seasonal cycle in eddy occurrence, with the Natal Pulse causing more variability than any seasonal signal. A thermistor array deployed in the ...

Ship-based acoustic Doppler current profiler (S-ADCP) technology, used in survey mode, has enabled near- synoptic views of the in situ 3-D current field in the KwaZulu-Natal (KZN) Bight to be elucidated for the first time. Data acquired by the research vessels RS Africana and RS Algoa in June 2005, September 2007, March 2009 and July 2010 are presented. Each S-ADCP dataset showed similar circulation characteristics whereby the continental slope and outer shelf of the KZN Bight were strongly influenced by the south-westward flowing Agulhas Current. This was particularly evident in the extreme north between Cape St Lucia and Richards Bay where the shelf is narrowest and velocities exceeded 200 cm s−1. The widening of the bight to the south moves the Agulhas Current further from the coast, resulting in a diminishing velocity gradient on the outer shelf which terminates around the midshelf axis. The southern region of the bight was mostly influenced by the Durban cyclonic eddy (Durban Eddy), and in June 2005 ...

Off the east coast of South Africa, robotic ocean gliders deployed in the Agulhas Current capture new data that help us better understand how energy dissipates in the ocean.

Cruise data sets, satellite remote sensing observations, and model data analyses are combined to highlight the existence of a coastal surface poleward flow in the southwest of Madagascar: the Southwest MAdagascar Coastal Current (SMACC). The SMACC is a relatively shallow (