In this study, 5 years (987 swaths) of high resolution wind speeds, derived from Advanced Synthetic Aperture Radar data collected over the Agulhas Current region, are studied to investigate the effect of warm, high intensity currents on the ocean's surface roughness and resulting derived wind fields. The wind data are derived using the CMOD5.n GMF with CFS reanalysis wind data as direction input. The CFS direction data are validated using ASCAT derived wind observations Globcurrent ocean current velocity data is used to investigate the difference between the satellite derived wind speeds compared to surface velocities of the current and the true wind speed. The, so called, current-relative effect is investigated for different wind direction regimes, namely: upcurrent, downcurrent, crosscurrent west and crosscurrent east. Our analyses are conducted for 6 locations of interest, evenly spaced along the Northern Agulhas Current. MODIS, SEVIRI and OSTIA SST data are used as proxy for locating the core of the Agulhas and it's temperature fronts, as well as to investigate wind speed modifications as a result of ocean-atmosphere energy transfer. It is found that higher resolution SAR derived winds have a greater ability to represent higher intensity and smaller scale wind features in comparison to winds derived from Scatterometers. A combination of the current relative effect and SST-atmospheric heating for upcurrent wind directions results in a sharp increase in mean wind speeds over the inshore boundary of the current of between 5m/s and 7m/s (50−60%). Individual events can reach as high as 15m/s (100%) over 10′s of kilometres. For downcurrent winds, the expected current relative effect is overridden by increased wind speeds of up to 5m/s (40%) across the entire current due to the influence of SSTs. The mean effect of SSTs on wind speeds has a stronger effect than the current relative effect on wind speed changes over the current. The wind speed differences are best represented under moderate wind speeds, between 5−15m/s. This investigation will contribute to future satellite wind speed derivations to identifying new wind speed and surface roughness altering effects. It will also serve to increase understanding of high resolution wind features and sharp changes over ocean features.

Includes bibliographical references. / The Southern Benguela upwelling system is particularly susceptible to Harmful Algal Blooms (HABs), most of which are attributed to dinoflagellate species. Dinoflagellates are favoured by stratified conditions. Consequently, temporal or spatial variations in ocean and atmospheric conditions that favour stratification will encourage HAB development. Temporally, prolonged relaxation of the dominant equatorward wings during late summer typically results in quiscent phases in upwelling which promote stratification and bloom development.

This thesis investigates the October to December (OND) rainfall variability over the mainland region of southeastern Africa in relation to El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole/Zonal Mode (IODZM) for the period 1950 to 1999. An empirical orthogonal function (EOF) analysis of OND rainfall field revealed that the north-south aligned areas of the eastern SADC are located in different covariability regions. This meridionally aligned dipole rainfall anomaly configuration is captured only in the dominant principal component (PC1) making it possible for the opposing rainfall anomalies of the two regions to have a common trigger. However, ENSO which has typically been invoked as the main cause for significant rainfall variability over this region cannot adequately explain this dipole rainfall anomaly pattern. The results of statistical analyses strongly indicate that positive Indian Ocean Dipole/Zonal Mode (IODZM) phase events lead to a rainfall dipole such that floods occur over the north east of the region (Tanzania) at the same time as droughts over the south east of the region (Zimbabwe, northern South Africa). On the other hand, negative IODZM phase events do not seem to lead to the reverse rainfall anomalies suggesting that the positive and negative rainfall dipoles may have rather different causes. Thus, contrary to conventional knowledge, the ENSO association to this dipole rainfall anomaly pattern is not robust but appears to be the result of the well known ENSO-IODZM connection. However, when analysed over 31-year overlapping segments, the results indicate that the sensitivity of this rainfall pattern to the IODZM is weakening from the 1990s onwards whereas that of ENSO appears to be strengthening.

Includes abstract. / Includes bibliographical references (p. 44-46). / The study found that the meridional positions and gradients of MADT exhibit interannual variability as well as considerable trends over the 15-year time-series. The meridional zones along the Greenwich Meridian also displayed clear trends over the period from June 2002 - November 2007 in integrated SST. The trends suggest a warming and shift in the climate state driving some of the variability in the ACC, which is consistent with other scientific studies.

Includes bibliographical references (leaves 132-141). / Pierre Florenchie / This study is framed by three questions: firstly, could the Regional Oceanic Modelling System (ROMS) reproduce the seasonal cycle of the equatorial Atlantic? Secondly, what is the nature of the link between remote forcing in the western equatorial Atlantic and Benguela Niños/Niñas? Thirdly, what is the impact of these events on the equatorial Atlantic Ocean SST and circulation patterns? The results obtained suggest that the model is very sensitive to different wind stress forcing, particularly in respect of the impact on the mixed layer characteristics. As a result the equatorial upwelling is overestimated in both temporal and spatial scales.

Includes bibliographical references. / Fisheries are of great economic importance on the South African West Coast (the Southern Benguela). The St Helena Bay region is a key nursery habitat for these fisheries because of its retention, upwelling and stratified water column characteristics. However, these characteristics also result in other outcomes such as hypoxia and harmful algal blooms (HAB's) which impact on the habitat suitability character of the system. A nearshore, episodic poleward current has been observed in this region, and it is believed that this current plays an important role in the incidence of HABs as well as hypoxia events. The drivers and dynamics of this nearshore, episodic poleward current have not been clearly understood, nor thoroughly investigated, due to the complexity of the scales and processes. However, the importance of this current in transporting harmful algae from the north into St Helena Bay and its role in habitat hypoxia has emphasized the need to understand its dynamics.

Bibliography: pages 68-74. / South African oceanographers were engaged in collecting hydrographic and biological sea truth data in order to calibrate the CZCS measurements from the NIMBUS-7 satellite over the Benguela Upwelling region and along the east coast of South Africa during the period 1978 to 1981. A brief overview of the CZCS validation programme and its application to the South African marine environment is given, followed by an analysis of level-Til CZCS data obtained from NASA for the region 10° - 60°S, and 10° - 100°E. This area includes the Benguela Upwelling system on the continental shelf, and the Southern Ocean with the Subtropical Convergence zone south of Africa. High annual values (5mg m⁻³) of chlorophyll occurred in the Benguela shelf region, typical of other upwelling systems in the world ocean, and the data shows a strong interannual signal in the seven years of composited data from 1978-1985, with maxima in 1982. Two distinct regimes were found in the Benguela Upwelling system, the seasonal variations of pigment concentration in the northern and southern Benguela regions being out of phase. In the Southern Ocean, the values of chlorophyll were generally low (0.15mg m⁻³) with the strongest signal (1.5mg m⁻³) found at the southern border of the Agulhas retroflection region and its frontal boundary with the colder subantarctic water to the south. The high values of chlorophyll found in this region are ten times the typical open Southern Ocean values. There is a clear interannual signal in the CZCS data for this Subtropi£al Convergence region, which has a low value in 1979 rising to a maximum in 1981 and then decreasing to another low value in 1985. There appears to be no pronounced seasonal variation in the Subtropical Convergence data. Reasons for the strong signal in the surface chlorophyll concentrations at the front between the Agulhas Return Current and the Southern Ocean are discussed, and it is shown that the Agulhas Plateau sets up a topographic Rossby wave in the Agulhas Return Current, which can be clearly identified in the CZCS signal. The large expanse of the Subtropical Convergence region is found as able to sustain a standing stock of phytoplankton similar in magnitude to that on the Benguela shelf, for limited periods of time. A brief analysis of sea surface temperature versus chlorophyll concentration shows the relationship between the two parameters to take the form of an inverted parabola, having a temperature window within which maximum chlorophyll concentrations are found.

Intraseasonal convection oscillation over the northeastern and southwestern Tanzania during MAM and DJF seasons respectively are examined using December, 1979 to May, 1994 pentad (5-day mean) Outgoing Longwave Radiation (OLR) as an indicator of convective cloud distribution. Area-averaged OLR indices are derived for the two areas. Time series of OLR indices for MAM and DJF indicate large quasi-periodic OLR fluctuations in some years and small fluctuations in other years. Periodogram analyses results reveal that dominant periodogram values for the oscillations were different in different years over both areas. Dominant periodogram peaks with periods more than 6 pentads (30 days) occurred 40% of the time on the average. Based on the pentad OLR time series plots deep convection and their precursors are composited. The time evolution of composite OLR maps reveal that patterns of low OLR values (indicating deep connection) shift north-eastwards coupled with low OLR values associated with mid-latitude troughs and linked to the ITCZ. Composite of kinematic and thermodynamic parameters associated with deep conJection and precursors are composited.

Fossil fish scales hold potential for ellucidating past fish population fluctuations. A system of classification for scales from the pilchard, Sardinops ocellata, and the anchovy, Engraulis capensis, is presented. Both species show an unexpected range of scale types. The classifications reduce errors in distinguishing between the scales of the two species to ±2,5%. Scale loss from these fish is quantified under laboratory conditions. Pilchard lose 1,56 scales/fish/day due to death and 1,50 scales/fish/day due to deciduousness over their expected lifetimes. For anchovy the figures are 2,42 scales/fish/day (death) and 0,48 scales/fish/day (deciduousness). Application of these scale-loss studies to scales preserved in the anaerobic sediments off Walvis Bay, Namibia, shows that deciduousness is the dominant process contributing scales to the sediments. This basic information on pilchard and anchovy scale loss is used to interpret counts of scales in the laminated interval of a core taken from the diatomaceous muds off Walvis Bay. This pilot study shows that: i) the Namibian Fishery was dominated by pilchard in the past as it was prior to the collapse in the early 1970's and, because of this, is distinctly different from the anchovy/anchovetta-dominated east Pacific systems; and ii) major pre-fishery stock fluctuations do appear to be reflected in the sedimentary record. Further scale studies on larger sediment samples are recommended to ellucidate the Namibian fish stock fluctuations.

Includes bibliographical references (p. 105-112). / The aim of this dissertation is to use satellite-derived images for the study of spatial and temporal variations in SST and in concentration of surface chlorophyll-a of the main oceanographic features off Angola. SST time-series over the 1987 to 2002 were derived from Meteosat 5-day SST composites with a spatial resolution of about 5-6 km in Angolan waters and a thermal resolution of 0.5°C. Chlorophyll-a data were from a 5-day composite of SeaWiFS GAC (4.5 km 'Global Area Coverage') images. Such images were available on a format comparable with the Meteosat SST composite images and covered the period 1998 to 2004.