Cape Point Research Articles

Historical imprints on genetic population structure in direct-developing beach whelks (Bullia digitalis)

Marine organisms often show deep genetic divergence between lineages that are characterized by shallow population structure. The distinction of historical and contemporary demographic forces in creating and maintaining these genetic patterns is crucial for management and conservation. In this study, we examined the genetic population structure of Bullia digitalis, a lecithotrophic sandy beach whelk that lacks a pelagic larval phase and is thus expected to show limited connectivity between populations. Mitochondrial (mt)DNA cytochrome c oxidase subunit I (COI; 540 bp, n = 214) and a reanalysis of allozyme data (14 loci, n = 735) among populations along the cool southeast Atlantic (west) and warm-temperate southwest Indian Ocean (south) coasts of southern Africa showed a strong phylogeographic break across Cape Point with mtDNA (ΦRT = 0.6, p < 0.001), but a weak break with allozymes (FRT = 0.002, p = 0.004). MtDNA gene flow occurred asymmetrically from the west to the south coast. Although there was no mtDNA differentiation between populations on either side of that break (ΦSR = 0.0), there was weak but significant isolation by distance (IBD) among south coast samples (r2 = 0.20, p = 0.039). In contrast, significant allozyme differentiation was detected on small spatial scales but without overall IBD. MtDNA mismatch analysis indicated a recent range expansion, suggesting historic population expansions, most likely during periods of lower sea levels and greater habitat continuity along southern African shores. Thus, the apparent mtDNA connectivity among populations of beach whelks likely reflects historic, rather than contemporary, gene flow.

Statistical Study of Sensor Data and Investigation of ML-Based Calibration Algorithms for Inexpensive Sensor Modules: Experiments From Cape Point

Statistical Study of Sensor Data and Investigation of ML-Based Calibration Algorithms for Inexpensive Sensor Modules: Experiments From Cape Point

EXAMINING CURRENT AND FUTURE CHALLENGES OF SEA LEVEL RISE ON COASTAL NATIONAL PARKS

Over the past decade, the increase in extreme weather events requires each sector to reflect on vulnerabilities to develop strategies for ramping up climate action. Owing to the shortage of climate data, significant knowledge gaps exist in some sectors of society and the economy, particularly in developing countries such as Africa. This has caused challenges for adaptation and resilience building as governments and other stakeholders cannot leverage knowledge for policy and practice and to seek funding for climate change action. This study responds to this knowledge by examining sea level challenges and their implications on coastal national parks in South Africa. The key question for this study is the most at-risk areas regarding sea level in coastal national parks and the implications of sea level on coastal national parks. The study utilises primary, secondary and archival data to arrive at conclusions. The study also uses climate change modelling data from SSP2-4.5 and SSP3-7.0. The study found that the most vulnerable coastal park in South Africa is the Garden Route National Park, which has the highest sea level rise, which will result in the Knysna section followed by the Cape Point section of Table Mountain, which will see the areas witnessing a 1m rise in sea level around 2100. Sea level rise is a threat to infrastructure, heritage, beaches, tourism employees and tourist safety, to mention but a few. The study recommends scaling up climate change action to assist the parks in adapting and building climate change resilience.

Impact of a recent wildfire on tortoises at Cape Point, South Africa, and implications for the interpretation of heated bones in the archaeological record

Heat-altered bones are a common occurrence in the archaeological record, and their analysis can provide detailed insights into past fire use behaviors and subsistence strategies. Heat-altered bones, however, may also result from natural fire events such as wildfires that are unrelated to human activity. We currently lack robust reference materials from natural fire events, analyzed using the same methodological approaches as we apply them to archaeological assemblages, that can be used to differentiate between natural and anthropogenic origins of heated materials. Here, we studied an assemblage of 50 tortoises that perished in a brushfire in Cape Point, South Africa. We used a combination of (1) zooarchaeological assessments of heating pattern and (2) infrared spectroscopy including a heating experiment to reconstruct heating temperatures with the aim to document the fire impact on the tortoise remains. For both approaches, we used statistical models to develop and test predictions that can also be applied to archaeological material. Our analyses suggest a quickly moving and low temperature brushfire in the study region with a generally low and superficial heating impact on the tortoise remains. However, we also observed several high-temperature alterations with calcination and speculate that naturally occurring fuel sources controlled the severity of the fire impact. The evidence of heating on the tortoise was unpatterned. We conclude that temperature alone presents a low confidence deciding factor between wildfires and campfires while skeletal heating pattern, in concert with other contextual analysis, may be able to facilitate this distinction with more localized heating signatures for campfires.

Wet season chemical composition of atmospheric wet deposition at Cape Point

The measurement of precipitation chemistry enables the assessment of the temporal and spatial evolution of the chemical composition of the atmosphere associated with atmospheric physical and chemical mechanisms. The aims of this study were to report the chemical composition of rainwater collected at a marine environment, i.e. the Cape Point Global Atmosphere Watch (CPT GAW) station from 2004 to 2012. As expected, the volume weighted mean (VWM) concentrations of Na+ (298.64 μEq.L-1) and Cl- (354.18 μEq.L-1) were significantly higher compared to the VWM concentrations of other ionic species, as well as compared to the VWM concentrations thereof at the sites in the South African interior. The average pH of rainwater was slightly lower than the pH of unpolluted rainwater, mainly due to NO3- associated with the occasional influence of the Cape Town metropole. In contrast to the sites situated in the north-eastern South African interior, where anthropogenic SO42- was the major constituent in rainwater, SO42- at CPT GAW was entirely associated with marine air with no anthropogenic contribution. It was also indicated that 94% of the chemical content at CPT GAW can be attributed to the marine source.

Inter‐Annual Variability of the Along‐Shore Lagrangian Transport Success in the Southern Benguela Current Upwelling System

AbstractA 3‐km resolution regional ocean model is used to investigate the role of wind‐driven coastal circulation and mesoscale variability on the inter‐annual variability of transport success in the southern Benguela between Cape Point (34°S) and St Helena Bay (32°S) from 1992 to 2011. Lagrangian particles are released within the top 100 m of the water column along an across‐shore transect off Cape Point. Transport success is given by the ratio of the number of particles that reach St Helena Bay over the total number of particles released. The analysis of transport success anomalies and their relationship with the local circulation and wind forcing reveal that there is no single driver of the inter‐annual variability. The transport success variability of particles released on the shelf (depths <300 m) mainly depends on their capacity to remain embedded within the coastal Benguela Jet. Nevertheless, peaks in offshore Ekman transport and episodic occurrence of a poleward inner‐shelf counter‐current contribute to negative anomalies. For particles released on the outer shelf edge (depths >500 m), across‐shore transports induced by mesoscale eddies are the main contributors to transport success variability. Rare passage of Agulhas rings near the shelf edge can induce strong offshore advection of particles into the open ocean. In contrast, shelf‐edge cyclonic eddies favor the onshore transport of particles originating from the outer shelf edge and thus contribute to increasing transport success.

Coast of Eastern Antarctica as the source of atmospheric mercury during austral summer

Observations of atmospheric mercury over the Southern Ocean and Antarctica are still limited. We performed a ship cruise from Cape Point, South Africa, to the Indian Bharati station, Prydz Bay, Antarctica (42.72°S 24.52°E to 69.41°S 76.19°E, 2015.01.18–27) and subsequently stationed the ship near the Bharati till 2015.02.19. We report relatively constant values of gaseous elemental mercury (GEM) concentration during the cruise (1.08 ± 0.08 ng/m3, n = 541) and highly variable values at the coast (0.96 ± 0.36 ng/m3, n = 1050). Meteorological parameters: relative humidity, temperature and solar radiation had almost negligible effect on GEM concentration (adjusted R2 = 0.09 in multiple linear regression model) during the ship cruise and a limited effect on GEM (adjusted R2 = 0.34) during the ship stay at Bharati. Analysis of NOAA-HYSPLIT 24-h back trajectories showed that all trajectories were extremely shallow during the ship cruise and therefore results likely were affected by the marine boundary layer rather than long-range transport. On the other hand, highly variable values of GEM near Bharati station were explained as a result of interplay of shallow and descending air masses coming from the Antarctic coast and from the terrain. These factors together with temperature dependency indicated that the coast of Antarctica acted as a temperature-driven source of GEM during the austral summer. Measurements were performed with a portable atomic absorption (CVAAS) mercury analyzer model Gardis-5. In our knowledge, this was the first time the CVAAS method was successfully applied for the background Antarctic observations.

The first national scale spatial and temporal analysis of surface CO2 over South Africa utilising satellite retrievals

ABSTRACT South Africa is the dominant continental source region of CO2 fossil fuel emissions. This is a result of the strong dependence of its economy on fossil fuels. However, the observations of atmospheric CO2 in South Africa are inadequate. The country has the Global Atmospheric Watch (GAW) Cape Point station as the only site with long-term ambient CO2 monitoring record. In this study, satellite data retrieved from the Tropospheric Emission Spectrometer (TES) instrument on board the Aura satellite from Dec 2004 to Dec 2009 is used for the first time to quantify the spatial distribution of CO2 over South Africa, as well as to determine its annual variability at selected sites. The study found that the surface CO2 foot print in South Africa resembles the industrial CO2 emission sources spatial distribution, particularly during the summer and autumn. In winter and spring seasons the surface CO2 foot prints are spatially expanded as a result of contributions of emissions from biomass and domestic fossil fuel combustion. The surface levels of CO2 at the study areas have been increasing during the period of the analysis.

The Use of Social Media as a Marketing Tool by Tourist Attractions: Influence on Cognitive, Affective and Behavioural Consumer Attitudes

Social media has an enormous influence on the manner in which people look for and distribute data, and select a tourist destination. Hence, research was undertaken to ascertain the role of social media as a communication and marketing tool for Cape Town tourist attractions (Cape Point, Groot Constantia Wine Estate, V&A Waterfront, Table Mountain Aerial Cable Way and Kirstenbosch Botanical Gardens) via the analysis of tourists’ cognitive, affective and behavioural attitudinal responses. The results revealed that tourists displayed positive cognitive/affective and affective/behavioural attitude associations towards social media usage by the Cape Town tourist attractions. Several demographic and usage characteristics resulted in significant positive attitudes regarding Cape Town tourist attraction social media sites, viz. South African and African tourists; mobile device access; new social media users; daily log-ons; Black, Indian and Coloured tourists; and tourists who used the local Rand currency. The findings could be used by Cape Town tourist attractions to improve their social media platforms, and thereby the effectiveness as a marketing tool. The study makes an original contribution since few tourism-related studies investigated the hierarchy of effects model in terms of social media and most previous research only considered usage and demographic characteristics as descriptive measures.

Rising sea level and its implications on coastal tourism development in Cape Town, South Africa

While there is agreement among tourism role-players on tourism's potential to contribute to socio-economic and environmental development, the industry is under severe threat from the increased impact of climate variability and change. This study examines the implications of rising sea level on coastal tourism in Cape Town, South Africa. Making use of mean sea level data from permanent sea level markers, remote sensing and field observations, supported by key informant interviews, the study found that coastal tourism is under threat from rising sea level. Current and projected rising sea level, as well as other extreme weather events such as the increased storm intensity trigger massive waves and tides that result in storm surges, which overtop and encroach into the land surface area. At least 80% of the city's 2019/2020 Blue Flag beaches are now under threat from rising sea level and coastal erosion. The study also found that some of the iconic tourist attractions such as the Cape Point, V&A Waterfront, Robben Island and several beaches along the False Bay area are under the same threat. Other tourism facilities under threat of weather extremes from climate change include servitudes, coastal roads, railway facilities and tidal pools: all threatening the attractiveness of some resorts. Management implicationsRising sea level is a huge challenge that requires innovative solutions for the city of Cape Town. Given the threat that the industry is facing, there is a need for a public-private partnership aimed at ensuring that there are sufficient resources to help the tourism sector is capable of adapting to climate change. Increase insurance cover is a must to protect businesses from anticipated increased damage from rising sea levels and associated weather extreme events. Continued risk assessment is a must to ensure the industry is abreast with the continued changes which are threats to coastal tourism resorts and infrastructure.

Accounting for linefish dependency in management of the South African small pelagic fishery

To further implement an ecosystem approach to management of the small pelagic fishery in South Africa, we attempted to develop functional relationships between spatialised time-series of the biomass of three small pelagic fish species and the catch per unit effort (CPUE) of four linefish species (i.e. species caught on hook and line, excluding longlines) that could be used to account for the forage needs of dependent predators. Granger causality tests indicated significant effects of anchovy Engraulis encrasicolus biomass on silver kob Argyrosomus inodorus and yellowtail Seriola lalandi CPUE, significant effects of sardine Sardinops sagax biomass on geelbek Atractoscion aequidens CPUE, but no significant effects of biomass of west coast redeye round herring Etrumeus whiteheadi and east coast redeye round herring Etruemus wongratanai on any linefish CPUE. Sequential t-test analysis of regime shift (STARS) indicated temporal matching in regimes between anchovy biomass east of Cape Agulhas (EoCA) and yellowtail west coast (west of Cape Point) CPUE, and between sardine biomass EoCA and geelbek southwest coast (Cape Point to Cape Infanta) CPUE. Convergent cross mapping found no causality for anchovy biomass EoCA on yellowtail west coast CPUE but causality in the reverse direction. A high degree of causality in both directions for sardine biomass EoCA and geelbek southwest coast CPUE was observed, indicating strong predator–prey interaction, and a highly significant linear relationship between sardine biomass EoCA in year n–1 and geelbek southwest coast CPUE in yearn was obtained. This functional relationship should be considered for inclusion as a proxy for ecosystem state in management procedures that adopt the ecosystem approach to fisheries for the South African small pelagic fishery.

Atmospheric mercury in the Southern Hemisphere – Part 2: Source apportionment analysis at Cape Point station, South Africa

Abstract. Mercury (Hg) contamination is ubiquitous. In order to assess its emissions, transport, atmospheric reactivity, and deposition pathways, worldwide Hg monitoring has been implemented over the past 10–20 years, albeit with only a few stations in the Southern Hemisphere. Consequently, little is known about the relative contribution of marine and terrestrial Hg sources, which is important in the context of growing interest in effectiveness evaluation of Hg mitigation policies. This paper constitutes Part 2 of the study describing a decade of atmospheric Hg concentrations at Cape Point, South Africa, i.e. the first long-term (> 10 years) observations in the Southern Hemisphere. Building on the trend analysis reported in Part 1, here we combine atmospheric Hg data with a trajectory model to investigate sources and sinks of Hg at Cape Point. We find that the continent is the major sink, and the ocean, especially its warm regions (i.e. the Agulhas Current), is the major source for Hg. Further, we find that mercury concentrations and trends from long-range transport are independent of the source region (e.g. South America, Antarctica) and thus indistinguishable. Therefore, by filtering out air masses from source and sink regions we are able to create a dataset representing a southern hemispheric background Hg concentrations. Based on this dataset, we were able to show that the interannual variability in Hg concentrations at Cape Point is not driven by changes in atmospheric circulation but rather due to changes in global emissions (gold mining and biomass burning).

Emissions and Marine Boundary Layer Concentrations of Unregulated Chlorocarbons Measured at Cape Point, South Africa.

Unregulated chlorocarbons, here defined as dichloromethane (CH2Cl2), perchloroethene (C2Cl4), chloroform (CHCl3), and methyl chloride (CH3Cl), are gases not regulated by the Montreal Protocol. While CH3Cl is the largest contributor of atmospheric chlorine, recent studies have shown that growth in emissions of the less abundant chlorocarbons could pose a significant threat to the recovery of the ozone layer. Despite this, there remain many regions for which no atmospheric monitoring exists, leaving gaps in our understanding of global emissions. Here, we report on a new time series of chlorocarbon measurements from Cape Point, South Africa for 2017, which represent the first published high-frequency measurements of these gases from Africa. For CH2Cl2 and C2Cl4, the majority of mole fraction enhancements were observed from the north, consistent with anthropogenically modified air from Cape Town, while for CHCl3 and CH3Cl, we found evidence for both oceanic and terrestrial sources. Using an inverse method, we estimated emissions for south-western South Africa (SWSA). For each chlorocarbon, SWSA accounted for less than 1% of global emissions. For CH2Cl2 and C2Cl4, we extrapolated using population statistics and found South African emissions of 8.9 (7.4-10.4) Gg yr-1 and 0.80 (0.64-1.04) Gg yr-1, respectively.

A New Background Method for Greenhouse Gases Flux Calculation Based in Back-Trajectories Over the Amazon

The large amount of carbon stored in trees and soils of the Amazon rain forest is under pressure from land use as well as climate change. Therefore, various efforts to monitor greenhouse gas exchange between the Amazon forest and the atmosphere are now ongoing, including regular vertical profile (surface to 4.5 km) greenhouse gas measurements across the Amazon. These profile measurements can be used to calculate fluxes to and from the rain forest to the atmosphere at large spatial scales by considering the enhancement or depletion relative to the mole fraction of air entering the Amazon basin from the Atlantic, providing an important diagnostic of the state, changes and sensitivities of the forests. Previous studies have estimated greenhouse gas mole fractions of incoming air (‘background’) as a weighted mean of mole fractions measured at two background sites, Barbados (Northern Hemisphere) and Ascension (Southern hemisphere) in the Tropical Atlantic, where the weights were based on sulphur hexafluoride (SF6) measured locally (in the Amazon vertical profiles) and at the two background sites. However, this method requires the accuracy and precision of SF6 measurements to be significantly better than 0.1 parts per trillion (picomole mole−1), which is near the limit for the best SF6 measurements and assumes that there are no SF6 sources in the Amazon basin. We therefore present here an alternative method. Instead of using SF6, we use the geographical position of each air-mass back-trajectory when it intersects the limit connecting these two sites to estimate contributions from Barbados versus Ascension. We furthermore extend the approach to include an observation site further south, Cape Point, South Africa. We evaluate our method using CO2 vertical profile measurements at a coastal site in Brazil comparing with values obtained using this method where we find a high correlation (r2 = 0.77). Similarly, we obtain good agreement for CO2 background when comparing our results with those based on SF6, for the period 2010–2011 when the SF6 measurements had excellent precision and accuracy. We also found high correspondence between the methods for background values of CO, N2O and CH4. Finally, flux estimates based on our new method agree well with the CO2 flux estimates for 2010 and 2011 estimated using the SF6-based method. Together, our findings suggest that our trajectory-based method is a robust new way to derive background air concentrations for the purpose of greenhouse gas flux estimation using vertical profile data.

Atmospheric mercury in the Southern Hemisphere – Part 1: Trend and inter-annual variations in atmospheric mercury at Cape Point, South Africa, in 2007–2017, and on Amsterdam Island in 2012–2017

Abstract. The Minamata Convention on Mercury (Hg) entered into force in 2017, committing its 116 parties (as of January 2019) to curb anthropogenic emissions. Monitoring of atmospheric concentrations and trends is an important part of the effectiveness evaluation of the convention. A few years ago (in 2017) we reported an increasing trend in atmospheric Hg concentrations at the Cape Point Global Atmosphere Watch (GAW) station in South Africa (34.3535∘ S, 18.4897∘ E) for the 2007–2015 period. With 2 more years of measurements at Cape Point and the 2012–2017 data from Amsterdam Island (37.7983∘ S, 77.5378∘ E) in the remote southern Indian Ocean, a more complex picture emerges: at Cape Point the upward trend for the 2007–2017 period is still significant, but no trend or a slightly downward trend was detected for the period 2012–2017 at both Cape Point and Amsterdam Island. The upward trend at Cape Point is driven mainly by the Hg concentration minimum in 2009 and maxima in 2014 and 2012. Using ancillary data on 222Rn, CO, O3, CO2, and CH4 from Cape Point and Amsterdam Island, the possible reasons for the trend and its change are investigated. In a companion paper this analysis is extended for the Cape Point station by calculations of source and sink regions using backward-trajectory analysis.

Investigating the Large-Scale Transport of a Volcanic Plume and the Impact on a Secondary Site

Volcanic plumes can be transported across vast distances and can have an impact on solar ultraviolet radiation (UVR) reaching the surface due to the scattering and absorption caused by aerosols. The dispersion of the volcanic plume from the Puyehue-Cordón Caulle volcanic complex (PCCVC) eruption was investigated to determine the effect on aerosol loading at Cape Point, South Africa. The eruption occurred on 4 June 2011 and resulted in a plume reaching a height of between 9 and 12 km and was dispersed across the Southern Hemisphere. Satellite sulphur dioxide (SO2) observations and a dispersion model showed low concentrations of SO2 at the secondary site. However, satellite observations of volcanic ash and ground-based aerosol measurements did show increases between 10 and 20 June 2011 at the secondary site. Furthermore, there was good agreement with the dispersion model results and observations from satellites with most of the plume located between latitudes 40°–60° South.

There are three species of Chrysaora (Scyphozoa: Discomedusae) in the Benguela upwelling ecosystem, not two.

Chrysaora (Pèron Lesueur 1810) is the most diverse genus within Discomedusae, and 15 valid species are currently recognised, with many others not formally described. Since Chrysaora fulgida (Reynaud 1830) was first recognised as occurring off the south west (SW) coast off South Africa, the species has been variously synonymised with Chrysaora hysoscella (Linnaeus 1767) and Chrysaora africana (Vanhöffen 1902). Using DNA evidence alongside multivariate tools to analyse quantitative morphometric and meristic data, as well as information from the cnidome, we unambiguously separate C. fulgida from C. hysoscella; we resurrect C. africana as a valid species and recognise a new species, Chrysaora agulhensis sp. nov. Full descriptions of C. fulgida, C. africana and C. agulhensis sp. nov. are provided. The species have different geographical patterns of distribution around the region, with restricted areas of overlap: C. agulhensis sp. nov. is found along the southern coast of South Africa and over the Agulhas Bank, C. fulgida extends from Cape Point in South Africa to southern Angola, and C. africana can be found from southern Namibia northwards to the Gulf of Guinea. The species can be readily separated in the field by a combination of tentacle/lappet number and shape, colour patterns and the form of the oral arms.

Life history, distribution and seasonal movements of a threatened South African endemic seabream, Chrysoblephus gibbiceps

The red stumpnose Chrysoblephus gibbiceps (Sparidae) is a South African endemic seabream that has been severely depleted by fishing. A total of 678 C. gibbiceps were sampled by line and trawl fishing for a study of their morphology, age, growth, reproduction and diet. In addition, catch records from three time-periods since 1897 were interrogated for distribution patterns and movement behaviour. The sex ratio was 1.5:1 in favour of males. The length–weight relationship, W = 9.32 × 10−5 LF2.811, indicates hypoallometric growth. The bulbous head of large males is a secondary sexual characteristic. A von Bertalanffy growth model was fitted to age data obtained using otolith analyses: LF = 429.9 × (1 – e−0.113(t – (−3.799)). The maximum recorded age was 48 years, which is among the highest in seabreams, though the species matures after only 3 years. The gonadosomatic index (GSI) of ripe females (4.5%) was comparatively low, and the two-month-long early-summer spawning season was short compared with that of other sympatric seabreams. The very low GSI of ripe males (1.6%) suggests courtship battles and polygamy. The species feeds over low-profile reefs and consolidated sediments. The principal prey are ophiuroids. Although its trophic level is 3.7, C. gibbiceps has a low-nutrition diet. Historical and current catch data confirm a distribution from Cape Point (southeastern Atlantic) to southern KwaZulu-Natal Province (western Indian Ocean). There is evidence for localised migratory patterns, now partly lost due to severe population depletion. Whereas protogyny and resident behaviour have been suggested as traits that render seabreams vulnerable to fishing pressure, C. gibbiceps is a shoaling gonochorist that has collapsed due to fishing.

Atmospheric Toluene and Benzene Mole Fractions at Cape Town and Cape Point and an Estimation of the Hydroxyl Radical Concentrations in the Air above the Cape Peninsula, South Africa

Benzene and toluene, emitted into the atmosphere from a number of common anthropogenic activities, pose a significant human health risk. The mole fractions of toluene and benzene were measured at t...

Twenty-one years of passive sampling monitoring of SO2, NO2 and O3 at the Cape Point GAW station, South Africa

Sulphur dioxide (SO2), nitrogen dioxide (NO2) and ozone (O3) are considered typical inorganic gaseous pollutants in the atmosphere. The aim of this study was to assess long-term seasonal and inter-annual trends of a 21-year SO2, NO2 and O3 passive sampling (monthly means) dataset collected at the Cape Point Global Atmosphere Watch (CPT GAW) station. Comparison of the concentrations of these gaseous species with other IGAC DEBITS Africa measurement sites indicated that levels of these species were generally similar to other African inland ecosystems, but lower compared to an industrial site in southern Africa. The SO2, NO2 and O3 monthly mean concentrations showed seasonal patterns, which can be attributed to various factors influencing levels of these species at CPT GAW. These factors are generally season specific, which include changes in meteorological conditions and source contributions. Higher NO2 concentrations were also attributed to increased microbial activity in the wet season. The O3 seasonal pattern corresponded to the NO2 seasonality, which was attributed to their related chemistry. SO2 and NO2 concentrations displayed inter-annual variability, while O3 did not indicate significant inter-annual fluctuations. The seasonal and inter-annual variability was explored with a multilinear regression model, in which global, regional and local meteorological factors, as well as population growth were included. Modelling results indicated that variances in SO2 concentrations were predominantly influenced by changes in global forcing factors. Global, regional and local factors played a significant role in NO2 trends, which included the influence of population growth and associated increased anthropogenic activities. It was also established that variances in O3 concentrations were predominantly associated with regional and local factors. Trend analysis indicated that SO2, NO2 and O3 concentrations remained relatively constant over the 21-year sampling period at this background site in the Southern Hemisphere.