Includes bibliographical references. / Sea surface temperature (SST) fluctuations and changes around southern Africa have important consequences on regional weather, climate and the marine ecosystem. SST is a good indicator for upwelling strength in the Benguela Current system and therefore is linked to bio logical activity in that region. SS T is an important driver of the air-sea exchange of moisture and energy, especially in the Agulhas Current where high latent and sensible heat fluxes occur. It is important to quantify SST trends with accuracy for the long term monitoring and characterisation of weather, climate and marine ecosystem in southern Africa, especially in the context of climate change. Here various 1° x 1° SST datasets are used to calculate yearly time series, inter-annual fluctuations and trends in key oceanic regions of southern Africa. OI SST, Hadley SST, NOCS SST and ER SST (which has 2° x 2° resolution) are used in this study. I start calculating trends and inter- annual fluctuations for various domains and dataset in the recent satellite era since 1982 to compare the non-satellite products NOCS SST and ER SST with the satellite products Hadley SST and OI SST. The idea is to validate the no n-satellite products since 1982 and then use them to calculate trends around southern Africa before 1982. Trends and inter-annual fluctuation in the Angola Benguela Current system and the Agulhas Current retroflection system are therefore presented for all datasets for the 1982 - 2012 period. The datasets show different trends and different timing or amplitude of inter- annual variability. This prevents the estimation of changes in the region with confidence before the satellite era which was the initial objective of the study. The main reason is that ER SST is a 2° x 2° dataset and maybe not adequate for upwelling region and the Hadley SST 1° x 1° dataset include satellite data from 1980 which creates some non-homogeneity in time and probably an artificial cooling at the coast from the 1980’s when satellite data is introduced in the dataset to patch the observational gaps. It is therefore not advisable to use Hadley SST for trend studies including 1982 onwards. From 1982 to 2012 in the Benguela upwelling system, whereas OI SST and Hadley SST show mainly cooling trends of different magnitude, NOCS SST and ER SST show warming trends with NOCS showing significant (p < 0.05) warming trends which is suspicious. In the Northern Benguela and Retroflection all datasets show warming trends for the 1982 - 2012 period except from NOCS SST.

Includes bibliographical references. / The Seychelles-Chagos Thermocline Ridge (SCTR) is a region of upwelling present at 55°E- 90°E and 5°S-12°S in the southwest tropical Indian Ocean. It is a region of strong ocean-atmosphere interactions due to the high variability of the thermocline depth caused by the local Ekman pumping. Sea-viewing Wide Field-of-view Sensor (SeaWiFS) has shown high variability of surface chlorophyll-a (SChl-a) in the SCTR region. The Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO) have also driven significant interannual variation of the depth of 20°C isotherm (D20) and SChl-a in the southern tropical Indian Ocean. A 50-years hindcast (RUN58-07) from a coupled bio-physical model was used to study the SChl-a concentration on an annual time scale and the interannual variability of D20 and SChla in the SCTR in response to IOD and ENSO events. Initial analysis revealed a high overestimation of SChl-a in the 50-year run. Therefore, a 44-years hindcast (RUN58-01) of the same coupled model was taken into consideration. Comparisons with observations show that the RUN58-07 reproduces the D20 and SSH better than the RUN58-01 but the RUN58-01 shows better agreement with SeaWiFS. Results reveal that the SCTR exhibits an annual cycle of SChl-a concentration, with a peak in austral winter (June-August) due to the strong southeasterlies, increasing wind stirring and induced upwelling. Vertical sections of the SCTR also indicate that an increase in surface concentration in austral winter is compensated by a decrease in subsurface phytoplankton blooms. Composite figures show that IOD events exhibit a greater influence on the subsurface and surface variability in the SCTR region. The IOD deepens and shoals the D20 in the SCTR and eastern Indian Ocean respectively whereas ENSO displays a weaker and less-extensive influence on the D20. The spatial distribution of SChl-a in the Indian Ocean is completely disrupted by IOD during which the SCTR becomes oligotrophic whereas the eastern Indian Ocean becomes highly productive. ENSO, however, does not display any significant biogeochemical signature in the SCTR. This study should improve our understanding of the interannual variability of the thermocline depth and chlorophyll-a in the SCTR region; and for the optimization of the management of fishery resources and marine ecosystems.

Widespread flooding over parts of Malawi, Mozambique, and Madagascar occurred in January 2015. An impact assessment by the World Bank indicated huge damage to property, infrastructure, and agriculture over several regions in south-eastern Africa. The flooding was associated with tropical storm Chedza that developed in the Mozambique Channel on 11 January 2015. This study investigates the atmospheric circulation and potential mechanisms responsible for the heavy rainfall event that occurred between 11 and 17 January over Mozambique and Malawi using the Weather Research and Forecasting (WRF) model, the Global Forecast System (GFS) atmospheric reanalysis, satellite derived rainfall and wind data, and station rainfall data. Tropical Rainfall Measuring Mission (TRMM) rainfall estimates and rainfall station data indicated that southern Malawi and northern Mozambique experienced the majority of rainfall during the early stages of tropical storm Chedza while Madagascar experienced heavy falls when tropical storm Chedza tracked over the island on January 17. Furthermore, analysis of the station data revealed that the heavy rainfall over Mozambique occurred between 11 and 13 January with some stations recording about 80 % of their total January 2015 rainfall as resulting from this event. The WRF model run of the event indicated a low level easterly to southeasterly onshore flow over southern Mozambique that interacted with a northwesterly monsoonal flow to westerly flow along the northern flanks (periphery) of the storm in the northern Mozambique Channel, leading to surface moisture flux convergence in the regions of heavy rainfall. Furthermore, moisture from the southwest Indian Ocean was advected into the region during the heavy rainfall. It is suggested that multiple favourable factors which included strong moisture fluxes from the southwest Indian Ocean and equatorial South Indian Ocean, near surface convergence over the areas of heavy rainfall, and strong uplift acted together to create favourable conditions for the development of tropical storm Chedza and the associated heavy rainfall.

Includes bibliographical references. / Several species of marine organisms occurring off the southern African coast have been found to be identical to those occurring in the Madagascan coastal water although the reason for this is unknown. It has been proposed that eddies act as a vector of transport for planktonic larvae from the Madagascar island to the southern African east coast. In this study it is shown that eddies spawned off southern Madagascar entrain chlorophyll-a rich coastal waters into their periphery. This is indicative of the mechanism whereby organisms could become entrained in eddies. Approximately one eddy per year, usually cyclonic, interacts with the southern Madagascan coast, then from its origin crosses the southern Mozambique Channel and arrives at the African coast where it dissipates. By tracking eddies and combining their trajectories with drifter data and satellite remote sensing observations of ocean colour, it is shown that chlorophyll-a rich waters are entrained within the eddies, and these waters are mostly conserved during their passage across the channel. This study suggests that biota may be transported from Madagascar to Africa in eddies, providing further evidence that eddies are potentially a viable mechanism for the transport of organisms across the southern Mozambique Channel.

Analysis of tide gauge sea level observations of varying durations in the southwest Indian Ocean and the East coast of Africa (Lamu, Mombasa, Zanzibar, Durban, Port La Rue and Port Louis) show variability which are related to global, regional time scales, local weather and climatic changes, oceanographic and hydrological forcing that manifest in both short and long time scales. The investigations on the tide gauge sea level observations are conducted through the separation of the total sea level measurements into the contributing components (tides and residuals) using a Matlab in built software (t-tide). Short time scale sea level variability in the southwest Indian Ocean is due to the effects of tides which exhibit tidal range variations with latitude and shelf width, storm surges resulting from tropical cyclones passage especially in the mid-latitude region, atmospheric pressure fluctuations over the surface of the sea and local wind fields. Sea surface temperature variations during summer and winter result in differential heating of the ocean surface and contribute to the observed sea level variability at seasonal time scale especially in the region 25°S and southwards where the temperature differences are large. The equatorial region is characterized by a near constant sea surface temperature that sustains thermal expansion of the upper layer of the ocean water throughout the year. Monsoon periods show significant and variable wind speeds that impact on sea level variability in the southwest Indian Ocean and the East coast of Africa and are greatest during the summer monsoon (from June to August). On longer time scales (Interannual and decadal), sea level variations in this region is mostly influenced by the El Nino Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). During the 1997/98 El Nino event, the sea levels are significantly higher than normal at the coast and the islands. During the 2000/2001 La Nina, the sea levels are significantly lower than normal at the coasts in the southwest Indian Ocean. Indian Ocean Dipole effects are significant in the southwest Indian Ocean during the period 2006 through to 2008 and are more enhanced in 2007. The annual highest sea levels in this region are influenced by the year to year changes in weather pattern and the perigean cycle of the tides on a 4.4 year period but their secular trends are not statistically significant.

In this study, we investigate the role that the solubility and biological pumps have on CO₂ variability across the Agulhas Current system ( Agulhas Current and the Agulhas Return Current). The Agulhas Current system transports heat and salt from the Indian Ocean into the South Atlantic Ocean via the Agulhas leakage, which influences the Atlantic Meridional Overturning Circulation (AMOC). This study presents for the first time a characterization of the role the Agulhas Current system (Agulhas and Agulhas Return Currents) has on the uptake of anthropogenic CO₂. Fugacity of carbon dioxide (fCO₂ ) values were obtained from a ship-based underway pCO₂ (partial pressure of carbon dioxide) system and the air-sea CO₂ fluxes were computed using 6-hourly wind speeds from the NOAA Blended Sea Winds. An experiment was conducted during the Crossroads scientific monitoring line in May 2013, where surface dissolved inorganic carbon, total alkalinity and CO₂ flux were compared between the Agulhas and Agulhas Return Currents and the region directly south over the Agulhas Plateau. Our findings highlighted that the solubility and biological pumps played minimal to no role in the drawdown of carbon across the sub-Tropical zone and the Agulhas Current system (Agulhas and Agulhas Return Currents), due to opposing effect between chlorophyll and temperature on pCO₂ that explained why although there was carbon drawdown by primary production in the Agulhas and Agulhas Return Current regions, this does not play a role in enhancing the air-sea exchange of CO₂. The solubility pump was responsible for CO₂ in the sub-Antarctic zone. The biological and solubility pumps were responsible for CO₂ sink in the Agulhas Plateau eddy. The highest CO₂ flux in the study was observed in the Agulhas Plateau eddy at a flux value of -8.12 mmolC.m-².day-¹ due to the cooler mean sea surface temperature of ~16.5 °C. This is the first time that such as study has been undertaken and aims to provide a better understanding of the role of Western Boundary Currents such as the Agulhas Current has in the uptake of CO₂.

Eddies within oceans act as vehicles, transporting smaller bodies of water, with certain oceanographic characteristics, from one place to another within a larger body of water. The South West Indian Ridge [SWIR] is a topographically complex bathymetric feature which amplifies the production of mesoscale eddies in and around the Antarctic Circumpolar Current [ACC]. Within the Southern Ocean [SO], a section of this ridge - the Andrew Bain Fracture Zone [ABFZ] - has been found to be the starting line of an eastward extending eddy corridor. Earlier research shows an area of diminishing mesoscale variability within this corridor which extends down from 45°S to approximately 60S. A recent study focused on a southward extending anticyclonic eddy corridor and proved its existence. The anticyclonic [warm core] eddies which are propagating south, not previously investigated through in situ means, were observed during the 2014 Marion Island Relief Cruise [MIRC2014] aboard the SA Agulhas II. Two anticyclonic mesoscale eddies [one juvenile and one mature] were bisected with transects of conductivity, temperature and depth stations and expendable bathythermograph deployments. This paper used the in situ data captured during the MIRC2014 to study the internal structure of the two eddies. The objectives of this study were also to examine both the recent and the historical trajectory characteristics of the southward advecting anticyclonic eddies, to confirm the origin of the two sampled eddies, and to assess the structural differences between the two anticyclonic eddies. This paper plots the behaviour of the anticyclonic mesoscale eddies found within the area of the southward eddy corridor, firstly using website available data collected over a two year period [May 2012 - May 2014] and then utilizing a previously compiled data set to plot the historical dynamics [October 1992 - April 2012]. The trajectories of the southward anticyclones during that time period were found to be predominantly southward, typically following the south west slope of the SWIR. The two MIRC2014 eddies were confirmed to originate from the ABFZ section of the SWIR. Each eddy had a similar grouping of water masses; Antarctic Bottom Water, Circumpolar Deep Water, Antarctic Intermediate Water, Winter Water and Sub-Antarctic Surface Water: water masses characteristic of the Antarctic Polar Frontal Zone [APFZ]. The in situ measurement and analysis of these eddies allowed the first comparison between a juvenile and a mature anticyclonic eddy in the recently discovered southward extending eddy corridor. Thermal section comparisons of these two sampled anticyclonic eddies showed that, over time, these anticyclonic eddies appear to shrink in surface diameter, deepen and lose heat to host waters. This loss of heat occurs due to the degradation of water mass boundary integrity over time and is theorised to accelerate as time passes. This study shows that the southward extending eddy corridor is a means of shifting heat and salt further south within the SO, large sections of which are sink areas for atmospheric CO₂. This poleward heat transport influences the capability of the SO to absorb atmospheric CO₂, since higher temperatures negatively affect the ocean's CO₂ uptake capability. The results of this study are proposed to be a catalyst for future in situ sampling across eddies in this area, in order that heat and salt transport, through this southward anticyclonic eddy corridor, can be monitored for fluctuations. As this carbon sink is vitally important with regards to climate change, the quantification of the heat and salt sources of the SO, which alter the SO's ability to absorb CO₂, is imperative.