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Includes bibliographical references., The two principal bottom-up drivers of the High Nutrient Low Chlorophyll (HNLC) characteristics of the Southern Ocean are light and nutrient (mainly dissolved iron) limitation ( Boyd , 2002; Mitchell et al., 1991), which have varying limiting roles over the growing season ( Boyd, 2002; Swart et al., 2014). This research commenced with an investigation of the meridional characteristics of primary productivity in the Atlantic Southern Ocean during austral summer 2008.

Includes bibliographical references, A recent study by Lenton et al., 2013, compared the mean seasonal cycle of air-sea CO₂ flux in the Southern Ocean(SO) over 1990 – 2009 period using five ocean biogeochemical models(BGMs) and atmospheric and ocean inversion models with monthly mean observations for the year 2000. This was done using a set of geographic boundaries to defined sub-domains of the SO consistent with the Regional Carbon Cycle and Assessment and Processes (RECCAP) protocol. Lenton et al., 2013 found that the seasonal cycle anomaly of the five BGMs better resolved observations of the air-sea CO₂ flux seasonal cycle in the SAZ, but was generally out phase with observations in the polar zone. In this study two setups of the ocean biogeochemical model NEMO PISCES was used to investigate the characteristics of the air-sea CO₂ flux seasonal cycle in the Southern Ocean in the period 1993- 2006. The study focused on two aspects i.e. (i) the sensitivity of air-sea CO₂ flux seasonal cycle to model resolution: comparing the ORCA2-LIM-PISCES (2° x 2° cos Ø) and PERIANT05 (NEMO-PISCES) (0.5° x 0.5° cos Ø) model configurations relative to climatological mean observations for the year 2000 (Takahashi et al., 2009) , and (ii) the sensitivity of air-sea CO₂ flux seasonal cycle to zonal boundary definition: comparing the air-sea CO₂ flux seasonal cycle and annual fluxes for three different boundaries i.e. Lenton 2013 RECCAP boundaries (44°S – 58°S and south of 58°S), geographic boundaries (40°S -50°S and south of 50°S) and dynamic boundaries (Sub-Antarctic Zone and Antarctic Zone, defined using climatological frontal positions). The seasonal cycle of the air-sea CO₂ flux in ORCA2 was found to be out of phase and overestimated the CO₂ flux compared to observations in almost all the sub-regions considered. The use of dynamic boundaries was found not to improve resolving observations seasonal cycle of air-sea CO₂ flux in both ORCA2 and PERIANT05. Boundary definition was found to affect the magnitude of ORCA2 annual air-sea CO₂ fluxes surface area based, where sub-regions of larger surface area gave larger annual CO₂ uptake and vice versa. This was mainly because ORCA2 air-sea CO₂ fluxes were found to show a general CO₂ in-gassing bias and spatially uniform in most parts of the SO and hence integration over a larger surface area gave larger annual fluxes. On the contrary PERIANT05 air-sea CO₂ fluxes spatial variability was not uniform in most parts of the SO however influenced by regional processes and hence annual fluxes were found not surface area based. The poor spatial representation and seasonal cycle sensitivity of ORCA2 air-sea CO₂ fluxes was found to be primarily due to lack or weak winter CO₂ entrainment and biological CO₂ draw down during the summer season. PERIANT05 on the contrary showed the effect of winter CO₂ entrainment, however maintains lack of or weak biological CO₂ draw down in the seasonal cycle. PERIANT05 was also found to show major weakness in the spatial representation of air-sea CO₂ fluxes north of the polar front with relative to T09 observations.

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 bibliographical references., An observational study was undertaken to determine the seasonality of the marine carbonate system of the southern Benguela focusing on three key points: the processes driving bulk stoichiometry, alkalinity production on the continental shelf, and the air-sea flux of CO2. Monthly samples were taken along the St. Helena Bay Monitoring Line in the southern Benguela for ten of the months in 2010. Samples were analysed for dissolved inorganic carbon (DIC) and total alkalinity (TA). Temperature, salinity, oxygen and nutrients were also measured.

Includes bibliographical references., Ocean Acidification through the uptake of anthropogenic CO₂ is resulting in a decrease in surface water carbonate ion concentration, a critical compound for marine calcifying organisms (Fabry et al., 2008; Orr et al., 2005). Natural seasonal variability is predicted to hasten the effects of Ocean Acidification in the Southern Ocean, resulting in possible surface water wintertime aragonite (the more soluble form of calcium carbonate) undersaturation (Ωarag< 1) south of the Antarctic Polar Front by the year 2030 (McNeil and Matear, 2008). An Ocean Acidification study was conducted to determine the seasonal and interannual variability in aragonite saturation state (Ωarag) at the Antarctic ice shelf between 4°E and 14°W and in the Eastern Weddell Gyre, during the Austral summers of 2008/2009, 2009/2010, 2010/2011 and 2011/2012. This study shows that at the Antarctic ice shelf andin the Eastern Weddell Gyre (EWG), seasonal summertime phytoplankton blooms were a critical factor in the observed decrease in summer surface water CO 2 and the subsequent increase in summer surface water Ωarag.