Includes bibliographical references. / Bromoform is mainly produced naturally by marine organisms. The production by microalgae however is not well quantified, and the mechanism by which phytoplankton produce bromoform is not fully elucidated. The production of this compound at the cellular level seems to be linked to oxidative stress via the use of the antioxidant enzyme bromoperoxidase (Manley and Barbero, 2001). However, no experiment has been conducted under bacteria-free conditions, which may bias the results because bacteria produce bromoform. Diatoms, which are wide spread in the open ocean, could be amongst the most important producers of bromoform. The purpose of this study was to quantify the effect of nutrient limitation and oxidative stress on bromoform production from axenic cultures of marine diatoms.

Rainfall variability in NW Madagascar and the kinematics and thermodynamics of flood-producing weather systems affecting the region are examined. Daily rainfall in the austral summer are used to select 16 cases for the composite analysis of flood events in the period 1987-1992. In addition two cases of flood events are studied individually. The first flood event occurred in 1991 and brought420 mm of rainfall in 24 hours at Maintirano during the passage of tropical cyclone (TC) Cynthia, an eastward moving TC from the Mozambique Channel. The second flood event occurred in 1992and brought 347 mm of rainfall in 24 hours at Mahajanga due to the passage of TC Bryna, a westward moving TC from the Indian Ocean. Inter-annual rainfall variability is correlated with the indices: TC day frequency, QBO and SOI, and a useful value is found with the first index but not with the two latter global indices. An intraseasonal analysis indicates that wet spells have a duration of 15 to 20 days. Daily spectra analysisof rainfall reveals the complexity of interplay between the convective forcing features. Cycles of 10-20 days are contributed by easterly waves, while 40 day cycles are produced by monsoon surges. The composite analysis identifies the following features: an eastward shift of active convection from Mozambique across Madagascar in conjunction with a surge of the NW monsoon and weakening of the easterlies in the lower troposphere. These factors promote TC genesis. Other supporting influences include the development of an anticyclonic circulation in the upper level over the island with north westward outflow. This often coincides with an east phase QBO, an upper level eastward moving mid-latitude trough and a persistent moisture flux convergence over the island throughout TC passage. The topography of Madagascar plays an important role in the intensification of the flood producing weather system by enhancing the cloud vortex in the NW region of the island.

Includes bibliographical references. / A model study was undertaken to investigate the optimization of sampling strategies for returning low-uncertainty sea-air CO₂ flux measurements in the Southern Ocean. Replicating Lenton et al. (2006) using the ORCA2/PISCES ocean biological model shows that sampling 4 times a year, every 2⁰ in latitude and every 40⁰ in longitude reduces the uncertainty of estimating annual CO₂ flux estimates such that sampling at a higher frequency does not reduce the total uncertainty in proportion to the increase in sampling effort.

Includes abstract. / Includes bibliographical references. / The northern Benguela, under the influence of the opposing forces of the poleward Angola Current and the eastern boundary Benguela upwelling regime is a highly variable environment. The impact of climate change, especially in warming water temperatures and the shifting position of the Angola Benguela Frontal Zone (ABFZ), may be compounding this variability. Biological responses such as shifts in temperate species away from the warming mid latitudes, towards the cooler poles are becoming evident. This study aimed to quantify the effects of these changes (in terms of temperature, dissolved oxygen and salinity) on the spatial distribution of an important inshore commercial, artisanal and recreational fishery species in the northern Benguela, Argyrosomus coronus (west coast dusky kob).

The Antarctic Circumpolar Current (ACC) within the Southern Ocean (SO) is the primary driver for global interoceanic exchanges. These exchanges form the foundation for the Meridional Overturning Circulation (MOC), a deep density driven circulation, which extends throughout the global oceans. The fronts of the ACC, consisting of several branches, separate zones of distinct water masses, thus identifying the location of the fronts and understanding their dynamics is of global importance. The GoodHope programme, is a repeat annual transect between South Africa and Antarctica, monitoring the exchanges within the Southeast Atlantic sector of the Southern Ocean. This is achieved through high resolution Expendable Bathythermograph (XBT) sampling. In this study XBT data over an eight year period (2004 – 2012) were investigated and analysed. One aim is to illustrate the variability of the fronts associated with the ACC using in-situ data from 21 transects during this eight year period. The Sub-tropical Front (STF) and Northern branch of the Sub-Antarctic Front (SAF-N) are seen to be the most variable with frontal latitudinal shifts ranging from 2-4° and 1-2° respectively. One cause of this high variability is the interaction of mesoscale features, particularly in the form of eddies and Agulhas rings. The southernmost fronts of the ACC, namely the Southern Antarctic Circumpolar front(sACCf), consisting of a Northern and Southern branch of the sACCf (sACCf-N and sACCf-S) and Southern Boundary (SBdy), also display high variability due to seasonality brought on by ice melt. The central fronts of the ACC, the Middle and Southern branches of the SAF (M-SAF and S-SAF)and Northern, Middle and Southern branches of the Polar Front (PF-N, PF-M and PF-S) remain throughout the eight year observations fairly constant, with shifts observed to be less than 1° of latitude. Grouping the Good Hope transects into austral summer periods, illustrates the di-pentadal nature of the STF, whereby the shifts are in response to mesoscale interactions. Comparing the mean position of the fronts and their position observed during a single winter cruise in July 2012, an overall Northward shift was observed with most of the fronts with significant shifts occurring in the SAF-N and PF-N. This is due to the outcrop of different water masses occurring further South ward and Northward respectively.

Bibliography: pages 96-103. / This thesis presents the results of a current meter experiment performed in the St Helena Bay - Cape Columbine region during winter 1982. The work, which forms part of the shelf dynamics programme undertaken by the Sea Fisheries Research Institute, attempts to identify the important time and spatial scales within the coastal currents and to investigate the relationship between the sub-inertial flow and low frequency variations in the coastal winds.

Includes bibliographical references (leaves 106-117). / This study forms the first step towards a comprehensive ocean colour satellite validation strategy for the Southern Benguela region, and underlines the value of a statistical radiometric validation as a prerequisite to any geophysical validation exercise. A radiometric validation exercise was performed using co-incident MERIS RR data and in situ radiometer data from a mooring in the Southern Benguela near Lambert's Bay during the late summer bloom seasons of 2005 and 2006. The data are typified by very high biomass conditions. Sources of error associated with the in situ data are assessed and the magnitudes quantified. The satellite data is examined with particular reference to uncertainty derived from the atmospheric correction processes, which perform unreliably in many of the matchup instances. Results show that the accuracy of the atmospheric correction does not appear to be related to the in-water constituents and is more likely due to atmospheric variability or aerosol features that are not addressed in the models employed by the correction processes. It is also shown that while the radiometric data display a consistent bias in the red region of the spectrum, good correlation with the satellite measurements is observed here under high biomass conditions, underlining the importance of the red wavebands for coastal remote sensing. Recommendations towards the development of a comprehensive regional validation strategy include the establishment of low-cost measurement protocols for high biomass conditions, as well as further investigations into regional atmospheric variability to improve confidence in the atmospheric correction procedures.

The Agulhas Retroflection south of Africa is a dynamic region from which mesoscale rings and eddies are shed. Hydrographic data collected simultaneously during two dedicated research cruises in the Agulhas Retroflection region in February - March 1987 are analyzed in conjunction with satellite data (Thermal Infrared Imagery and Geosat Altimetry). An unusual and possibly atypical situation is documented where a total of six Agulhas rings and eddies were present in the Retroflection region. Each of the six vortices exhibited characteristics specific to their age and location within the Retroflection region. Bibliography: pages 195-210.

Includes bibliographical references. / Surface station, satellite and NCEP re-analysis data are used to examine the evolution of two severe storms that occurred over the eastern coastal regions during South Africa's summer season 1998/99. The storms in November and December were both accompanied by heavy rainfall in two widely separated locations. The storm in December proved to be more severe as it resulted in flooding while tornadoes were reported in the Umtata and Hogsback regions of the Eastern Cape. Both storms appeared to result from interaction between a continental heat low, advection of warm moist air around an anticyclone in the South-west Indian Ocean and an approaching midlevel westerly trough. NCEP derived moisture flux diagrams and back trajectories of air parcels constructed from ECMWF data suggest that the Agulhas Current region was a major source of low level moisture for both storms. TRMM satellite imagery captured heavy rainfall above the high sea surface temperatures of the Agulhas Current. TRMM measurements of rainfall and latent heat in the atmosphere show that the high sea surface temperatures of the Agulhas Current modified the mesoscale environment above the current. To what extent the mesoscale environment above the Agulhas Current modified the synoptic situations over land could be answered using regional modeling and more frequent radiosonde data.

Includes bibliographical references. / The coastal upwelling regions along northwest Africa (the Canary system), southwest Africa (the Benguela system), North America (the California system), and South America (the Peru-Chile system) were studied and compared on a seasonal timescale. A 17 -year NOAA Pathfinder Sea Surface Temperature (SST) dataset with a spatial resolution of 9km was used to describe the large-scale temporal and spatial variability of upwelling within the four regions. An upwelling index (OSST) was derived in order to add to the patterns of upwelling variability described from the sea surface temperature. The upwelling index was also used to describe the similarities and differences between the four upwelling regions. A 10-year ERS wind stress dataset with a spatial resolution of 10 x 10 was used to derive the offshore Ekman Transport in each of the regions. The offshore Ekman Transport was used to supplement the description of SST's in each system. Principal Component Analysis was used to investigate the variance structure of the anomalies of the sea surface temperature in each of the four regions. The results of the principal component analysis are interpreted in terms of the underlying physical dynamics.