Browsing by Author "Collins, Charine"

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    Antarctic sea ice trends and its response to the Southern annular mode
    (2009) Collins, Charine
    Sea ice covers vast regions of the Southern Ocean and impacts on the climate as well as the plant and animal life of the region. The variability of sea ice in the Southern Ocean affects the entire food web of the region, from phytoplankton to Antarctic krill through to the apex predators such as seals and penguins. Sea ice variability is determined by shifts in the atmospheric temperature distribution and shifts in the atmospheric circulation. The Southern Annular Mode (SAM) is the primary mode of variability in the atmospheric circulation of the Southern Hemisphere. Despite the overall warming of Antarctica, sea ice extent and sea ice area show a positive trend in the Southern Ocean and all its sectors except in the Bellingshausen/Amundsen Seas sector which displays a negative trend for the period 1979-2007. The SAM index also shows a positive trend during this period indicating a shift towards the more positive phase. The monthly and seasonal correlations between the SAM index and sea ice concentrations display a dipole, with more ice occurring in the Ross Sea during the positive phase of SAM and less ice occurring in the Weddell Sea.
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    Building A Mean-state Of Oceanographic Properties (Temperature And Salinity) For The Kwazulu-natal Bight Using The Roms Model: A Contribution Towards Marine Protected Areas Analysis
    (2018) Malange, Mathabo Noxolo; Morris, Tamaryn; Collins, Charine; Lamont, Tarron; Ansorge, Isabel
    The KwaZulu-Natal Bight, located along the east coast of South Africa, is an important recruitment and nursery area for various marine species. In an effort to conserve a number of threatened species, two Marine Protected Areas (MPA) have been established in the Bight. The African Coelacanth Ecosystem Programme is conducting MPA analyses along the Bight through a series of biological and oceanographic studies and this study forms part of the oceanographic research component that will assist in the decision-making process of MPAs in the region. This study uses a 30-year, high-resolution, regional ROMS simulation to build a climatology representative of the mean-state of the Bight. The model is also used to investigate the seasonal and annual variability as well as the influence of the Agulhas Current on the shelf. The Bight was cooler and less saline than the surrounding waters and seasonal variation was limited to the upper 50 m of the water column. The depth of the Bight ranges from 50 m in the inner shelf to 100 m at the shelf edge in the central region of the Bight. In the northern and southern region of the Bight, the depth of the water column extends down to about 150 m at the shelf edge. In summer, surface temperatures were on average 4.8°C and 4.3°C warmer than in winter over the uThukela Banks and Aliwal Shoal respectively. Bottom temperatures at both MPAs had a mean seasonal variation of about 3°C. Salinity, a more conservative variable, showed little variability over the year throughout the water column except for at 50 m where lower salinities were observed in the winter months. Wavelet analysis showed that a strong annual (12 month) signal was dominant at the surface (10 m). Bottom temperatures displayed a weaker annual signal than the surface in addition to a slight semi-annual cycle. Further investigations indicated that the Agulhas Current influenced the Aliwal Shoal MPA more than the uThukela Banks MPA as they shared similar temperature values (at the surface and bottom) throughout the 30-year period. In contrast, the uThukela was cooler than the Agulhas Current by 0.5 to 1.5°C at the surface and 1 to 2.5°C at the bottom. These time series also enabled us to identify anomalous features such as the Natal Pulse that could have important implications for temperature-sensitive species in the area.
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    The dynamics and physical processes of the Comoros Basin
    (2013) Collins, Charine; Reason, Chris; Hermes, Juliet C
    The main objective of this thesis was to investigate the circulation in the ComorosBasin using observed and model datasets. These data were used to establish whether or not a Comoros Gyre exists and to investigate the nature of the eddy variability in the basin.The water masses in the Comoros Basin emulate those found further south in the Mozambique Channel. The presence of AAIW north of Madagascar confirmed that this water mass enters the Comoros Basin from the east while the presence of North Atlantic Deep Water showed that this water mass is capable of spreading northward over the Davie Ridge. The main currents in the Comoros Basin, the westward flowing NEMC and a poleward current along the western boundary, are under the influence of the monsoon winds. The NEMC intensifies during the Southwest monsoon in response to a strong wind jet which develops off the northern tip of Madagascar, whereas the poleward current weakens due to the opposing force imposed by the southwesterlies. Additionally, the circulation in the basin consist of meso-scale eddies of both polarities. Anti-cyclonic eddies, with lifespans of
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    The inter-annual variability in the onset of the enhanced chlorophyll-a east of Madagascar
    (2015) Oozeeraully, Yuneeda Bibi Naheed; Reason, Chris; Hermes, Juliet C; Collins, Charine
    Chlorophyll-a concentration is a measure of phytoplankton biomass and is therefore used as a proxy for primary production. The chlorophyll bloom occurring in the South western Indian Ocean is one of the major blooms in the open ocean and is subject to controversies about its formation, propagation and termination mechanisms. In this study, the region was divided into two sub-regions, the South East region (48°E-66°E, 24°S-30°S) and the East region (70°E-88°E, 24°S-30°S) and satellite datasets of chlorophyll-a, sea surface temperature, wind speed and direction and sea surface height were analysed. A bloom was characterized by twice the mean level of the sub-region (~0.08mg/m3) and three bloom years were identified: 2004, 2006 and 2008. The timing, propagation and termination of the bloom showed spatial and temporal variability. The wavelet analysis revealed a semi-annual signal for 2006 and 2008 and an annual one in 2004 due to the gradual decline in the concentration of chlorophyll-a. The transport of the bloom is affected by the passage of eddies where the concentration of chlorophyll-a is higher in the core and around the edges in cyclonic and anticyclonic eddies respectively. The bloom could be present at the sub-surface level throughout the years but is only apparent at the surface during specific years.