Cape Columbine Research Articles

Molecular screening of ticks of the genus Amblyomma (Acari: Ixodidae) infesting South African reptiles with comments on their potential to act as vectors for Hepatozoon fitzsimonsi (Dias, 1953) (Adeleorina: Hepatozoidae).

In South Africa, the role of reptilian ticks in the transmission of haemoparasites is lacking, in part, due to limited information on tick diversity and their associated haemoparasites. The aim of this research was to identify tick species parasitizing reptiles and to molecularly screen these ectoparasites for species of the blood apicomplexan genus Hepatozoon. Samples were collected from Ndumo Game Reserve, KwaZulu-Natal, and the Cape Columbine region, Western Cape. Reptiles collected included 2 snakes, 2 monitor lizards of a single species respectively, as well as 17 tortoises of four species. Ticks collected from these were morphologically identified as Amblyomma latum (n = 2) and Amblyomma marmoreum (n = 98), this identification was molecularly confirmed using 16S rRNA and CO1 genes. Screening for Hepatozoon was done by amplifying the 18S rRNA gene. A species of Hepatozoon, Hepatozoon fitzsimonsi, was identified from A. marmoreum ticks, with an overall prevalence of 10%. This Hepatozoon species, has been described parasitizing tortoises from southern Africa, and has been reported from ticks infesting tortoises from Kenya, East Africa. Even though ticks have been suggested to be the likely vector of this Hepatozoon species, with this supported by the findings of Hepatozoon-like developmental stages in ticks collected off of infected tortoises, a recent systematic revision placed this species in a newly erected genus Bartazoon, a genus vectorised by biting insects. The present study thus provides further support for ticks acting as the potential vectors of H. fitzsimonsi.

Rainfall and river flow trends for the Western Cape Province, South Africa

Climate change has the potential to alter the spatio-temporal distribution of rainfall, subsequently affecting the supply and demand of water resources. In a water-stressed country such as South Africa, this effect has significant consequences. To this end, we investigated annual and winter rainfall and river flow trends for the Western Cape Province over two periods: 1987–2017 and 1960–2017. Annual rainfall for the most recent 30-year period shows decreasing trends, with the largest magnitude of decrease at the SA Astronomical Observatory rainfall station (-54.38 mm/decade). With the exception of the significant decreasing winter rainfall trend at Langewens (-34.88 mm/decade), the trends vary between stations for the period 1960–2017. For the period 1987–2017, statistically significant decreasing winter trends were found at four of the seven stations, and range from -6.8 mm/decade at Cape Columbine to -34.88 mm/decade at Langewens. Similarly, the magnitudes of decreasing winter river flow at Bree@Ceres and Berg@Franschoek are greater for the more recent 30-year period than for 1960–2017. Correlation coefficients for Vilij@Voeliv rainfall and four river flow stations Berg@Franschoek, Bree@Ceres, Wit River@Drosterkloof and Little Berg@Nieuwkloof) are stronger for shorter periods (i.e. 1987–2017 and 2007–2017) than that for the longer period, 1960–2017. The Intergovernmental Panel on Climate Change emphasises the importance of studies to assist with model prediction uncertainties. To this end, our study expands the understanding of regional hydrological responses to rainfall change in the water stressed region of the Western Cape Province.
 Significance:
 
 Historical trend analyses provide the basis for future rainfall and river flow projections and also improve our understanding of hydrological responses to rainfall change, which is important for water resource planning and management in light of recent rainfall shortages experienced in the Western Cape region.
 Anthropogenic and natural influences on river systems must be taken into account when assessing the impact of rainfall changes on river flow because these factors ultimately affect water resource management.
 We identified decreasing winter rainfall trends across the Western Cape Province for the most recent three decades.

Shelf-edge jet currents in the southern Benguela: A modelling approach

Abstract The dynamics and seasonal variability of jet currents on the southern Benguela shelf-edge are investigated using a climatologically forced Regional Ocean Modelling System (ROMS) model. The jet is primarily forced by the intense horizontal gradients that exist across the southern Benguela shelf. These gradients are set up by nearshore cooling via the strongly seasonal upwelling regime and variable offshore warming by the advection of Agulhas waters. While the nearshore cooling is prevalent only during the spring and summer upwelling season, the offshore warming exists throughout the year. As a result intensified geostrophically adjusted currents exist throughout the year, particularly off the Cape Peninsula and Cape Columbine. However, the distinct shelf-edge jet features are most intense during upwelling seasons and extend, more or less continuously, from Cape Agulhas, the southern-tip of the continent, to Cape Columbine. The spring and summer jet off the Cape Peninsula reaches speeds of at least 0.7 m.s −1 , bifurcates as it moves northward. The branch that continues northward over the shelf goes on to feed the offshore branch of the Cape Columbine jet (over the 500 m isobath) and to a less extent the nearshore branch (over the 200 m isobath) that is locally enhanced by upwelling processes. During winter, the Cape Peninsula jet is more confined to the shelf region and goes on to feed the whole outer-shelf (200–500 m) region off and beyond Cape Columbine. An ageostrophic component associated with offshore non-linearities related to Agulhas influx causes the mean manifestation of the Cape Peninsula jet to broaden slightly (60 km) compared to its 40 km-wide geostrophic core which is situated over the 350 m isobath. The ageostrophic component is related to the generation of eddies that cause the isopycnals to flatten out.

Hydrographic variability in the St. Helena Bay region of the southern Benguela ecosystem

AbstractCross‐shelf distributions of temperature, salinity, water masses, and dissolved oxygen in St. Helena Bay revealed substantial vertical and seasonal variations. In the surface layers, nearshore and offshore temperature and salinity patterns differed, with bay‐scale variability linked to upwelling dynamics and coastal processes, while the offshore region was influenced by solar insolation. Spectral analysis revealed that an annual signal prevailed at most stations, and corroborated contrasting patterns between the offshore and nearshore regions, with phase differences suggesting shoreward propagation of the offshore temperature signal. The shelf was dominated by Modified Upwelled Water (MUW) and Subantarctic Mode Water (SAMW), which comprised the primary source of upwelled water. Clear zonation of MUW was evident across the shelf, resulting from seasonal variations in locations of the oceanic and bifurcated shelf‐break fronts. Dynamics within St. Helena Bay consistently differed from those further offshore, due to the influences of the shelf‐break front, Cape Columbine upwelling plume, and cyclonic recirculation, which appeared to be associated with an intraannual signal with a periodicity of 3–4 months. Persistent hypoxia in the bottom waters suggested the occurrence of a permanent reservoir of Low Oxygen Water (LOW). Seasonal shoreward and offshore expansion of LOW occurred throughout the upwelling season, with maximum extent reached during summer and autumn, due to the coupled effects of advection and local phytoplankton decay. While wind mixing ventilated the water column at nearshore stations in winter, and the onset of upwelling during spring introduced oxygen‐richer water from further offshore, hypoxia persisted in the center of the Bay.

Environmental Forcing of Red Tides in the Southern Benguela

The Southern Benguela cape upwelling plumes have inshore wind shadows prone to red tides in late summer. Their intensity and coverage are estimated by satellite fluorescence measurements in the period 1997–2012 and qualified by in situ reports. High satellite fluorescence cases are identified at daily to seasonal time scales, and characteristics of the upper ocean and lower atmosphere are studied using third generation reanalyses. A dominant feature is easterly winds over the Cape Peninsula (34°S, 18°E) induced by a ridging anticyclone-coastal low weather pattern. Over Cape Columbine (33°S), there is a wind shadow with cyclonic wind and current shear. Composite atmospheric profiles reveal a 4°C temperature inversion near 500 m that traps a coastal wind jet >6 m/s below 200 m. The composite shelf oceanography shows a relic upwelling plume below 10 m overtopped by warmer water near the coast, providing the thermal stratification needed for biotic aggregation. Data from the IPSL5 coupled climate model over the period 1980–2080 indicates that environmental conditions favoring red tides may become more frequent.

A study of Benguela upwelling system using different upwelling indices derived from remotely sensed data

Two upwelling indices (UI) derived from remotely sensed data, which are related to offshore Ekman transport (UIw) and the Sea Surface Temperature (SST) (UISST), are evaluated to study the spatial and temporal variations of the Benguela Upwelling System (BUS). The comparisons present the advantages and disadvantages of using UISST and UIW to scale upwelling intensity using the chlorophyll-a (Chl-a) concentration as a referential upwelling enhanced relative biomass proxy. The causes for the discrepancies of temporal and spatial variations of UISST, UIW and Chl-a in the BUS area are also discussed. By examining the UISST, UIW and Absolute Dynamic Topography (ADT) at 27–28°S, we find that the extension of the upwelling band is largely impacted by the anti-cyclonic eddy there. Furthermore, we discuss the Benguela Niños in 2006, and estimate the contribution from the wind effects to the total upwelling intensity off Hondeklip and Cape Columbine based on these remote sensing results.

Modeling the dispersal of Cape hake ichthyoplankton

The two Cape hake species of the southern Benguela ecosystem, the shallow-waterand deep-water hakes Merluccius capensis and M. paradoxus, are economically themost important marine resources in South Africa. Recruitment is a key process inthe dynamics of marine organisms, yet very little is known about the early lifehistory of Cape hakes, especially the location of spawning grounds and transportof eggs and larvae. For each species, ichthyoplankton dispersal off South Africa issimulated by coupling oceanographic simulations to an individual-based model inorder to track virtual individuals. Results indicate that the most favorable spawningareas for transport to nursery areas are located off the south-western coast and theeastern Agulhas Bank, and highlight partly different drift routes followed by thetwo ichthyoplankton species off Cape Columbine. Transport from spawning tonursery areas is the highest in austral winter for a spawning depth rangingbetween 0 and 100 m. These modeling results are in broad agreement with avail-able knowledge on the ecology of Cape hakes. The present work on Cape hakescomplements previous modeling studies on anchovy and sardine in the same area.Taken together, these studies underline the correspondence between cross-shore(for hakes) or alongshore (for anchovy and sardine) transport mechanisms and thespawning strategies used by these key species of the southern Benguela ecosystem.KEYWORDS: Merluccius spp.; Southern Benguela; larval dispersal; modeling

Sea surface temperature in False Bay (South Africa): Towards a better understanding of its seasonal and inter-annual variability

Two sea surface temperature (SST) products, Pathfinder version 5.0 and MODIS/TERRA are evaluated and used to study the seasonal and the inter-annual variability of sea surface temperature (SST) together with local SST and wind data in the vicinity of False Bay (Western Cape, South Africa). At the monthly scale, differences of up to 3°C are detected between the two products in the bay. In the northern half of the bay, SST is fairly well explained by seasonality. In contrast, the southern half exhibits a higher inter-annual variability in SST. The southern half of the bay and the Western Cape upwelling system (Cape Agulhas to Cape Columbine) share most of their variance. Furthermore, the inter-annual variability of SST in False Bay is correlated with both the Niño 3.4 index and local wind speed anomalies. El Niño (La Niña) events induce an equatorward (poleward) shift in the South Atlantic High pressure system leading to a weakening (strengthening) of upwelling favourable south-easterly. Those changes induce a warm (cold) SST anomaly along the West Coast of Southern Africa.

Copepod biomass, size composition and production in the Southern Benguela: Spatio–temporal patterns of variation, and comparison with other eastern boundary upwelling systems

Zooplankton sampling has been conducted biannually off the west and south-west coasts of South Africa since 1988, as part of the pelagic fish stock assessment cruises covering the continental shelf (0–200 m). Previously established relationships between body mass and growth rate were used to derive copepod production. Mean copepod biomass and annual production in the Southern Benguela between 1988 and 2003 were 2.1 g C m −2 and 134.4 g C m −2 yr −1, respectively. Biomass and production were higher during summer in four latitudinal areas, but seasonal variability was only significant for the central West Coast. This area, lying downstream from the Cape Columbine upwelling cell, supported the highest levels of copepod biomass (3.1 g C m −2) and production (545 g C m −2 d −1). Production during winter, when upwelling is minimal, contributed over one third of annual production in all four areas. Copepod biomass, daily production and size composition varied with latitude, season and year, and there were no consistent trends in interannual variability over the study period. Although biomass in the four major EBUS was of the same magnitude (usually <5 g C m −2), annual production estimates are an order of magnitude greater than those made four decades ago, with highest values for the Southern Benguela.

Dinoflagellate cyst production on the southern Namaqua shelf of the Benguela upwelling system

To study dinoflagellate cyst production in the southern Benguela, a sediment trap was deployed for a period of 3.5 years at a single station located downstream of the Cape Columbine upwelling cell on the southern Namaqua shelf. The cyst assemblage of surface sediments below the trap was also investigated. Twenty-nine different cyst types were recorded of which 25 were from the sediment trap, and 22 from the surface sediments. The flux of cysts followed a clear seasonal trend with an initial peak in spring followed by a major peak in autumn; with a mean flux for the entire period of deployment of 1.4 × 106 cysts m−2 day−1. Of the cysts recovered from the trap, those of heterotrophic dinoflagellates were six times more abundant than those of autotrophic dinoflagellates. The study also revealed the presence of cysts of species previously unrecorded in the plankton of the southern Benguela, specifically the toxic dinoflagellate Lingulodinium polyedrum.

Modelling the sensitivity of coastal winds over the Southern Benguela upwelling system to different SST forcing

Regional atmospheric modeling has been utilised in an attempt to resolve mesoscale spatial variations in wind stress forcing over the southern Benguela. The regional atmospheric model MM5 was used to simulate low-level coastal winds at high resolution (3 km) over the southern Benguela upwelling system for the March 2001 period and to assess the sensitivity to different resolution sea surface temperature (SST) forcing. The ability of a regional atmospheric model to resolve the mesoscale spatial variability in the local wind field which results from the adjustment of the large scale flow to regional topography and thermal gradients is demonstrated. The model output has been validated quantitatively through comparison with limited observations and qualitatively through comparison with wind fields observed in aircraft surveys conducted during previous summers. The regional model was capable of reproducing the qualitative effect of topographic forcing and thermal gradients on the equatorward flow. Local enhancement of low-level wind speed due to the interaction of the synoptic equatorward flow with both the Cape Peninsula and Cape Columbine was reproduced with associated bands of wind maxima, while lighter winds were seen in the lee of these capes. Increasing the spatial resolution of SST forcing to resolve cold SST's induced by upwelling is seen to enhance the mean response of low-level winds to coastal topography during the March 2001 event. These wind variations have important implications for coastal ocean dynamics and the development of extreme events in the region such as harmful algal blooms.

Nearshore currents on the southern Namaqua shelf of the Benguela upwelling system

Nearshore currents of the southern Namaqua shelf were investigated using data from a mooring situated three and a half kilometres offshore of Lambert's Bay, downstream of the Cape Columbine upwelling cell, on the west coast of South Africa. This area is susceptible to harmful algal blooms (HABs) and wind-forced variations in currents and water column structure are critical in determining the development, transport and dissipation of blooms. Time series of local wind data, and current and temperature profile data are described for three periods, considered to be representative of the latter part of the upwelling season (27 January–22 February), winter conditions (5–29 May) and the early part of the upwelling season (10 November–12 December) in 2005. Differences observed in mean wind strength and direction between data sets are indicative of seasonal changes in synoptic meteorological conditions. These quasi-seasonal variations in wind forcing affect nearshore current flow, leading to mean northward flow in surface waters early in the upwelling season when equatorward, upwelling-favourable winds are persistent. Mean near-surface currents are southward during the latter part of the upwelling season, consistent with more prolonged periods of relaxation from equatorward winds, and under winter conditions when winds were predominantly poleward. Within these seasonal variations in mean near-surface current direction, two scales of current variability were evident within all data sets: strong inertial oscillations were driven by diurnal winds and introduced vertical shear into the water column enhancing mixing across the thermocline, while sub-inertial current variability was driven by north–south wind reversals at periods of 2–5 days. Sub-inertial currents were found to lag wind reversals by approximately 12 h, with a tendency for near-surface currents to flow poleward in the absence of wind forcing. Consistent with similar sites along the Californian and Iberian coasts, the headland at Cape Columbine is considered to influence currents and circulation patterns during periods of relaxation from upwelling-favourable winds, favouring the development of a nearshore poleward current, leading to poleward advection of warm water, the development of stratification, and the creation of potentially favourable conditions for HAB development.

Contrasting wind patterns and toxigenic phytoplankton in the southern Benguela upwelling system

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 348:19-31 (2007) - DOI: https://doi.org/10.3354/meps07027 Contrasting wind patterns and toxigenic phytoplankton in the southern Benguela upwelling system A. Fawcett1, G. C. Pitcher2,*, S. Bernard1, A. D. Cembella3, R. M. Kudela4 1Department of Oceanography, University of Cape Town, Private Bag, Rondebosch 7700, Cape Town, South Africa 2Marine and Coastal Management, Private Bag X2, Rogge Bay 8012, Cape Town, South Africa 3Alfred Wegner Institute, Am Handelshafen 12, 27570 Bremerhaven, Germany 4Ocean Science Department, University of California, Santa Cruz, 1156 High Street, Santa Cruz, California 95064, USA *Corresponding author. Email: gpitcher@deat.gov.za ABSTRACT: The southern Namaqua shelf of the Benguela upwelling system, downstream of the Cape Columbine upwelling cell, is frequently subjected to a variety of harmful algal bloom (HAB) phenomena. Here, winds dictate most physical processes that are important to the development of HABs. Toxic algal cell concentrations and distributions, in relation to their respective toxin content, are compared over 2 autumn periods in successive years which exhibited clearly different wind patterns and hydrographic responses. During the first study period (15 March to 6 April 2005), several periods of relaxation from upwelling-favourable winds were associated with poleward nearshore currents and increasing levels of stratification. The phytoplankton community was dominated by dinoflagellates, including Dinophysis spp. and Protoceratium reticulatum, responsible for the production of toxins associated with diarrhetic shellfish poisoning and yessotoxins, respectively. In contrast, the subsequent study period (7 to 23 March 2006) was characterised by persistent upwelling-favourable winds, equatorward near-surface currents, and a cooler, moderately mixed water column. The phytoplankton assemblage was co-dominated by Pseudo-nitzschia spp. and Chaetoceros spp.; domoic acid concentrations corresponded closely with cell concentrations of Pseudo-nitzschia spp. Contrasting wind patterns, and their influence on water column structure and mesoscale circulation, led to predictably different assemblages of phytoplankton life-forms and their associated toxins. KEY WORDS: Southern Benguela · Upwelling · Harmful algal bloom · Diatom · Dinoflagellate · Algal toxins Full text in pdf format PreviousNextCite this article as: Fawcett A, Pitcher GC, Bernard S, Cembella AD, Kudela RM (2007) Contrasting wind patterns and toxigenic phytoplankton in the southern Benguela upwelling system. Mar Ecol Prog Ser 348:19-31. https://doi.org/10.3354/meps07027 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 348. Online publication date: October 25, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Characteristics of the surface boundary layer important to the development of red tide on the southern Namaqua shelf of the Benguela upwelling system

The southern Namaqua shelf, north of the Cape Columbine upwelling center, is particularly prone to red tide. Two influences of the surface boundary layer on the development of red tide in this area were investigated—the dynamics of the upper mixed layer in determining phytoplankton community composition and the role of mesoscale circulation in bloom concentration and transport. Two survey periods (18 February‐11 March 2000 and 13‐30 March 2001) are reported during which red tide, dominated by the dinoflagellate Gyrodinium zeta, formed in the area. A high degree of concordance between characteristics of stratification and groupings of phytoplankton demonstrated the importance of the upper mixed layer in determining species or life‐form selection and development. Ordination of across‐shelf phytoplankton samples revealed a consistent banded pattern, created by a wind‐induced upwelling plume, tending to isolate a nearshore zone from an offshore domain, thereby creating an area of retention on the coastal side of the plume, favoring development of dinoflagellate blooms. The appearance of red tide was clearly associated with increasingly stratified conditions driven by alongshore flow from the north, following periods of wind relaxation and consequent reversal of surface currents.

Reply to discussion by D. I. Cole

We strongly disagree with D.I. Cole’s contention that our use of strontium isotopes has not lead to any meaningful improvement in the chronostratigraphy of the Prospect Hill Formation exposed in the Tabakbaai Quarry (Franceschini and Compton, 2004). Interpretation of the complex stratigraphy of the West Coast has suffered from a lack of chronostratigraphy. The integration of radiocarbon, uranium disequilibrium and luminescent dating has greatly improved our understanding of upper Pleistocene and Holocene deposits of the West Coast (Roberts and Berger, 1997; Felix-Henningsen et al. , 2003; Compton and Franceschini, 2005). The challenge of the beach and aeolian deposits of the Prospect Hill Formation at Tabakbaai Quarry is that they are too old to date using these methods and so we applied the Sr isotope dating method because it has proved to be extremely useful in sorting out the complex late Cenozoic depositional history of the outer shelf offshore of Cape Columbine (Compton et al. , 2004; Wigley, 2005). Unfortunately the resolution of the Sr-derived ages we obtained is relatively poor mostly because the marine Sr isotope curve flattens out in the late Miocene (Farrell et al. , 1995) and …

Seasonal variation in phytoplankton in the southern Benguela: pigment indices and ocean colour

Pigment indices and satellite imagery were used to investigate the seasonal variation in phytoplankton in the southern Benguela, with the aid of monthly monitoring on two transect lines. Sea surface temperature images revealed the similarity in thermal conditions during autumn, winter and spring, with a broad zone of 11–14°C water extending northwards from Cape Columbine and a narrow zone extending south along the coast to the Cape Peninsula. In summer, warm water (18–20°C) intruded from the South Coast into the West Coast offshore region and cold water (10–12°C) prevailed inshore at particular upwelling centres. The phytoplankton response to these thermal conditions resulted in elevated chlorophyll a (2–15mg m –3) in the 11–14°C waters during all four seasons. The zones of elevated chlorophyll were generally broader from Cape Columbine northwards and narrower south of Cape Columbine to the Cape Peninsula. Pigment indices indicated that phytoplankton biomass was high in summer, but also quite extensive in the autumn and spring, with diatoms generally dominating inshore and small flagellates offshore. Diagnostic indices indicated that flagellates were prominent at inshore localities during all seasons, however, suggesting that this group contributed significantly to phytoplankton communities on the shelf.

Influence of sample size and sampling frequency on the quantitative dietary descriptions of a predatory fish in the Benguela ecosystem

Spatial and temporal variation in the diet and feeding intensity of snoek, Thyrsites atun, a top predator of the southern Benguela, was investigated to provide information on data requirements for accuracy of annual diets as inputs to ecosystem models. Appropriate sample sizes to produce accurate daily or event-scale diet descriptions were investigated by means of a posteori tests. Cumulative prey diversity curves showed that 55 (± 25) stomachs containing food are required to accurately quantify presence and absence data of prey species. Differences in the percentage contribution of dominant prey in consecutive and cumulative 10-stomach classes, indicates that a minimum of 75–80 (± 25) stomachs containing food are necessary to describe the proportion by weight of primary prey. Diets of snoek (proportions by weight) sampled inshore (shallower than 50 m and within 25 km of the coast) off the Cape Peninsula during six consecutive weeks (i.e.one day per week) in autumn 2001 were highly variable. Comparing diet for the six-week period with that of diets from consecutive 10-sample weekly units revealed 95% similarity at 70 samples per week. Seasonal diets between Cape Columbine and Cape Hangklip also varied, but there was no evidence of a predictable seasonal pattern in diet that could be related to prey life history; two-way nested ANOSIM revealed that seasonal prey proportions across years were statistically less similar than those within years. Snoek spawn offshore in winter/spring. Statistical differences between inshore (< 50m) and offshore (>150m) prey composition were largely influenced by the absence of anchovy Engraulis encrasicolus and much larger proportions of Cape hake Merluccius spp. and lanternfish Lampanyctodes hectoris in the offshore diet. Feeding intensity (in terms of proportions of fish with prey and mean stomach fullness) was strongly seasonal and highest during the spawning season. Sampling programmes for the southern Benguela should account for spatial and temporal variation in diet and feeding intensity of predators if accurate annual dietary descriptions are to be achieved. The results of this study indicate that a minimum of 70 snoek stomachs (containing food) should be collected at each sampling event.

Linking wind and interannual upwelling variability in a regional model of the southern Benguela

We quantify the wind contribution to the development of interannual sea surface temperature (SST) anomalies along the shelf of southern Africa. We compare numerical simulations that differ only in the amount of variability kept in the ERS1/2‐derived surface wind forcing. Surprisingly, most of the cold and warm episodes over the Agulhas Bank are strictly related to local fluctuations of the forcing, whereas the shelf of the west coast extending 400 km north of Cape Columbine is equally sensitive to open‐sea wind fluctuations. We diagnose the respective role of mesoscale eddy activity and of low frequency and intra‐monthly wind fluctuations in generating interannual SST variability. The fair degree of correlation obtained at a few locations between the model and concomitant observations confirms the interest of a regional numerical tool to study anomalous events in the Benguela system.

Timing and kinematics of the Colenso Fault: The Early Paleozoic shift from collisional to extensional tectonics in the Pan-African Saldania Belt, South Africa

The Colenso fault is a major northwest to southeast trending fault zone in the Pan-African Saldania Belt of the Western Cape Province in South Africa that is spatially closely associated with granitoids of the ~550 to 510 Ma Cape Granite Suite. Most of these granites were previously considered to be largely post-tectonic intrusions, but structural data presented in this study demonstrate the synkinematic emplacement of granitoids into, and along, the Colenso Fault. The kinematic analyses of shear zones and granite fabrics together with previously published and new geochronological data are combined to provide constraints on the complex kinematic history of the fault and the tectonic evolution of the hitherto poorly understood Saldania Belt. Early, strongly gneissose granitoids of the composite Darling batholith (547 ± 6 Ma) were emplaced during sinistral strike-slip movement along the Colenso fault. Both the timing of emplacement and penetrative deformation of the Darling batholith suggest an intrusion of the pluton during the main Pan-African collisional event in the Saldania Belt. The younger Trekoskraal granite intrudes synkinematically into dextral strike-slip faults related to deformation along the Colenso fault. Single-zircon ages from synkinematic aplites constrain the timing of dextral strike-slip shearing to 539 ± 4 Ma. The emplacement of the late-kinematic Cape Columbine granite during dextral strike-slip faulting indicates that dextral strike-slip kinematics along the Colenso fault continued at least until ~520 Ma. These results point to a reversal of strike-slip motion along the Colenso fault at ~540 Ma that coincides with the onset of uplift of rocks of the Saldania Belt. The final exhumation of the belt at ~515 to 520 Ma is marked by the near-surface emplacement of the last phases of the Cape Granite Suite, related subaerial volcanism, sedimentation of the coarse-clastic, fault-bounded Klipheuwel Group, and the overlying fluvial to shallow-marine sequence of the Mid-Cambrian Cape Supergroup. The temporal and spatial overlap between igneous activity and rift-type sedimentation indicates that a substantial part of the Cape Granite Suite was emplaced in an overall transtensional and/or extensional setting. During this time, the voluminous plutonism of the Cape Granite Suite most likely represented a significant heat input that also contributed to a thermal weakening of the crust. In view of the Early Paleozoic extensional setting suggested here, we interpret Ar-Ar mineral ages of ~500 Ma and post-orogenic plutonism that are widely documented from Pan-African belts throughout southwestern Africa to reflect a thermal event related to crustal thinning and associated mantle upwelling that follows the main phase of Pan-African collisional tectonics.

Fog-water harvesting along the West Coast of South Africa: a feasibility study

Many parts of the West Coast of South Africa experience severe water shortages throughout the year. Despite the meager rainfall, however, the region is subject to a high incidence of fog which might provide water for water-poor communities. This paper investigates the fog water potential of the area. Since fog water collection rates are to some extent dependent upon the spatial and temporal characteristics of fog, these aspects were investigated. Pilot fog collectors were erected at six West Coast sites and the water collection rates measured over a three to four year period. It was found that the incidence of fog is mostly confined to the coastal zone below the 200 m contour line with fog frequency decreasing with latitude within this zone. The highest water collection rates were recorded at Cape Columbine where volumes in excess of 2.5 l/m2 of collecting surface can be expected to be collected per day. Of this, approximately 90% is due to fog deposition alone, while rainfall contributes to the remaining 10%. The quality of the water is good and fit for human consumption. WaterSA Vol.28(4) 2002: 349-360