{"id":{"repo_id":"cape-town","oai_identifier":"oai:open.uct.ac.za:11427/29265"},"canonical_url":"https://search.dev.ndltd.org/etd/cape-town/oai:open.uct.ac.za:11427/29265","repository":{"repo_id":"cape-town","name":"University of Cape Town","base_url":"https://open.uct.ac.za/oai/request"},"display":{"title":"The biophysical processes controlling the South-East Madagascar Bloom","abstract":"Phytoplankton blooms are ecological hotspots in the ocean, and are fundamental to the biogeochemical cycling of elements, the storage of carbon and the ability to regulate the atmospheric carbon dioxide; and the life in the ocean. The South-East Madagascar Bloom, one of the largest blooms in the global ocean, coexists with the poleward flowing South-East Madagascar Current (SEMC), the eastward flowing South Indian Ocean Countercurrent (SICC) as well as westward-propagating surface and subsurface-intensified eddies. This austral summer bloom extends largely towards the open ocean, from the Madagascan coasts up to ~65°E and it exhibits an intriguing interannual variability. A variety of observational datasets as well as a high resolution coupled physical-biogeochemical model, based on CROCOPISCES, are used to explore the biophysical processes associated with the bloom and these westward-propagating eddies. Based on historical observational data, the bloom is shown to occur in a region of shallow mixed layer, with the surface layer exhibiting lower salinity, a possible signature of the coastal poleward flowing SEMC waters. The testing of various hypotheses revealed a dampening of the coastal current-driven upwelling south-east of Madagascar during bloom months. A dipole mesoscale feature is also prevalent close to the Madagascan coast during the bloom, from which a new hypothesis emerges. This new hypothesis states that the region south/south-east of Madagascar, influenced by local mesoscale turbulence, acts as a gate for the SEMC to flow either towards the African continent, or into the bloom region through an early retroflection, hence fertilizing the bloom. The model produces a sporadic enhancement of chlorophyll-a in the subsurface levels, associated with a low-salinity surface signature. The mean local circulation associated with the simulated bloom also reveals a dipole structure, as in observed datasets. Nitrate from subsurface levels (upwelling) as well as from the Madagascan coast (advection) is shown to influence the simulated bloom. A Lagrangian experiment shows dispersion of higher percentages of particles in the bloom region during bloom years and south of Madagascar during non-bloom years. Mesoscale eddies, originating close to Australia and which propagate westward towards southern Africa, can potentially impact the South-East Madagascar Bloom. In this study, a vast majority of these features have been shown to be subsurface-intensified eddies. A co-located eddy tracking dataset with Argo profiling floats are used to devise a subsurface-eddy identification method, which is based on the steric dynamic height anomaly of a specific eddy. Adding to the `eddy-zoo', these eddies are termed `SIDDIES' (South Indian ocean eDDIES), occurring as surface (surfSIDDIES) and subsurface (subSIDDIES) features. They travel along the latitudinal band range of 15°S to 35°S which we name the ‘SIDDIES corridor’. Advecting warm and fresh water during their propagation, cyclonic (anticyclonic) subSIDDIES contribute about 58% (32%) of the total eddy-heat flux in the South Indian Ocean. Anticyclonic subSIDDIES have also been found to be the sole, high-saline water eddy-conveyor towards the western South Indian Ocean. These eddies could also possibly transport nutrients throughout their journey, impacting the biogeochemistry of the ocean near Madagascar.","abstract_html":"Phytoplankton blooms are ecological hotspots in the ocean, and are fundamental to the biogeochemical cycling of elements, the storage of carbon and the ability to regulate the atmospheric carbon dioxide; and the life in the ocean. The South-East Madagascar Bloom, one of the largest blooms in the global ocean, coexists with the poleward flowing South-East Madagascar Current (SEMC), the eastward flowing South Indian Ocean Countercurrent (SICC) as well as westward-propagating surface and subsurface-intensified eddies. This austral summer bloom extends largely towards the open ocean, from the Madagascan coasts up to ~65°E and it exhibits an intriguing interannual variability. A variety of observational datasets as well as a high resolution coupled physical-biogeochemical model, based on CROCOPISCES, are used to explore the biophysical processes associated with the bloom and these westward-propagating eddies. Based on historical observational data, the bloom is shown to occur in a region of shallow mixed layer, with the surface layer exhibiting lower salinity, a possible signature of the coastal poleward flowing SEMC waters. The testing of various hypotheses revealed a dampening of the coastal current-driven upwelling south-east of Madagascar during bloom months. A dipole mesoscale feature is also prevalent close to the Madagascan coast during the bloom, from which a new hypothesis emerges. This new hypothesis states that the region south/south-east of Madagascar, influenced by local mesoscale turbulence, acts as a gate for the SEMC to flow either towards the African continent, or into the bloom region through an early retroflection, hence fertilizing the bloom. The model produces a sporadic enhancement of chlorophyll-a in the subsurface levels, associated with a low-salinity surface signature. The mean local circulation associated with the simulated bloom also reveals a dipole structure, as in observed datasets. Nitrate from subsurface levels (upwelling) as well as from the Madagascan coast (advection) is shown to influence the simulated bloom. A Lagrangian experiment shows dispersion of higher percentages of particles in the bloom region during bloom years and south of Madagascar during non-bloom years. Mesoscale eddies, originating close to Australia and which propagate westward towards southern Africa, can potentially impact the South-East Madagascar Bloom. In this study, a vast majority of these features have been shown to be subsurface-intensified eddies. A co-located eddy tracking dataset with Argo profiling floats are used to devise a subsurface-eddy identification method, which is based on the steric dynamic height anomaly of a specific eddy. Adding to the `eddy-zoo', these eddies are termed `SIDDIES' (South Indian ocean eDDIES), occurring as surface (surfSIDDIES) and subsurface (subSIDDIES) features. They travel along the latitudinal band range of 15°S to 35°S which we name the ‘SIDDIES corridor’. Advecting warm and fresh water during their propagation, cyclonic (anticyclonic) subSIDDIES contribute about 58% (32%) of the total eddy-heat flux in the South Indian Ocean. Anticyclonic subSIDDIES have also been found to be the sole, high-saline water eddy-conveyor towards the western South Indian Ocean. These eddies could also possibly transport nutrients throughout their journey, impacting the biogeochemistry of the ocean near Madagascar.","abstract_has_math":false,"creators":["Dilmahamod Ahmad Fehmi"],"institution":"Department of Oceanography","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Reason Christopher"],"committee_chairs":[],"committee_members":[],"year":2018,"date_issued":"2018","date_published":"2018","updated_at":"2026-07-22T22:22:38Z","subjects":[],"languages":["eng"],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/11427/29265","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Reason Christopher"]},{"key":"dc:creator","label":"Author","values":["Dilmahamod Ahmad Fehmi"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2019-02-04T12:21:26Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2019-02-04T12:21:26Z"]},{"key":"dc:date.issued","label":"Date","values":["2018"]},{"key":"dc:publisher.department","label":"Dc Publisher Department","values":["Department of Oceanography"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of Cape Town"]},{"key":"dc:type","label":"Dc Type","values":["Doctoral Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Doctoral"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["PhD"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["eng"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/11427/29265"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Phytoplankton blooms are ecological hotspots in the ocean, and are fundamental to the biogeochemical cycling of elements, the storage of carbon and the ability to regulate the atmospheric carbon dioxide; and the life in the ocean. The South-East Madagascar Bloom, one of the largest blooms in the global ocean, coexists with the poleward flowing South-East Madagascar Current (SEMC), the eastward flowing South Indian Ocean Countercurrent (SICC) as well as westward-propagating surface and subsurface-intensified eddies. This austral summer bloom extends largely towards the open ocean, from the Madagascan coasts up to ~65°E and it exhibits an intriguing interannual variability. A variety of observational datasets as well as a high resolution coupled physical-biogeochemical model, based on CROCOPISCES, are used to explore the biophysical processes associated with the bloom and these westward-propagating eddies. Based on historical observational data, the bloom is shown to occur in a region of shallow mixed layer, with the surface layer exhibiting lower salinity, a possible signature of the coastal poleward flowing SEMC waters. The testing of various hypotheses revealed a dampening of the coastal current-driven upwelling south-east of Madagascar during bloom months. A dipole mesoscale feature is also prevalent close to the Madagascan coast during the bloom, from which a new hypothesis emerges. This new hypothesis states that the region south/south-east of Madagascar, influenced by local mesoscale turbulence, acts as a gate for the SEMC to flow either towards the African continent, or into the bloom region through an early retroflection, hence fertilizing the bloom. The model produces a sporadic enhancement of chlorophyll-a in the subsurface levels, associated with a low-salinity surface signature. The mean local circulation associated with the simulated bloom also reveals a dipole structure, as in observed datasets. Nitrate from subsurface levels (upwelling) as well as from the Madagascan coast (advection) is shown to influence the simulated bloom. A Lagrangian experiment shows dispersion of higher percentages of particles in the bloom region during bloom years and south of Madagascar during non-bloom years. Mesoscale eddies, originating close to Australia and which propagate westward towards southern Africa, can potentially impact the South-East Madagascar Bloom. In this study, a vast majority of these features have been shown to be subsurface-intensified eddies. A co-located eddy tracking dataset with Argo profiling floats are used to devise a subsurface-eddy identification method, which is based on the steric dynamic height anomaly of a specific eddy. Adding to the `eddy-zoo', these eddies are termed `SIDDIES' (South Indian ocean eDDIES), occurring as surface (surfSIDDIES) and subsurface (subSIDDIES) features. They travel along the latitudinal band range of 15°S to 35°S which we name the ‘SIDDIES corridor’. Advecting warm and fresh water during their propagation, cyclonic (anticyclonic) subSIDDIES contribute about 58% (32%) of the total eddy-heat flux in the South Indian Ocean. Anticyclonic subSIDDIES have also been found to be the sole, high-saline water eddy-conveyor towards the western South Indian Ocean. These eddies could also possibly transport nutrients throughout their journey, impacting the biogeochemistry of the ocean near Madagascar."]},{"key":"dc:title","label":"Title","values":["The biophysical processes controlling the South-East Madagascar Bloom"]}]}],"canonical_facts":{"dc:contributor.advisor":["Reason Christopher"],"dc:creator":["Dilmahamod Ahmad Fehmi"],"dc:date.accessioned":["2019-02-04T12:21:26Z"],"dc:date.available":["2019-02-04T12:21:26Z"],"dc:date.issued":["2018"],"dc:description.abstract":["Phytoplankton blooms are ecological hotspots in the ocean, and are fundamental to the biogeochemical cycling of elements, the storage of carbon and the ability to regulate the atmospheric carbon dioxide; and the life in the ocean. The South-East Madagascar Bloom, one of the largest blooms in the global ocean, coexists with the poleward flowing South-East Madagascar Current (SEMC), the eastward flowing South Indian Ocean Countercurrent (SICC) as well as westward-propagating surface and subsurface-intensified eddies. This austral summer bloom extends largely towards the open ocean, from the Madagascan coasts up to ~65°E and it exhibits an intriguing interannual variability. A variety of observational datasets as well as a high resolution coupled physical-biogeochemical model, based on CROCOPISCES, are used to explore the biophysical processes associated with the bloom and these westward-propagating eddies. Based on historical observational data, the bloom is shown to occur in a region of shallow mixed layer, with the surface layer exhibiting lower salinity, a possible signature of the coastal poleward flowing SEMC waters. The testing of various hypotheses revealed a dampening of the coastal current-driven upwelling south-east of Madagascar during bloom months. A dipole mesoscale feature is also prevalent close to the Madagascan coast during the bloom, from which a new hypothesis emerges. This new hypothesis states that the region south/south-east of Madagascar, influenced by local mesoscale turbulence, acts as a gate for the SEMC to flow either towards the African continent, or into the bloom region through an early retroflection, hence fertilizing the bloom. The model produces a sporadic enhancement of chlorophyll-a in the subsurface levels, associated with a low-salinity surface signature. The mean local circulation associated with the simulated bloom also reveals a dipole structure, as in observed datasets. Nitrate from subsurface levels (upwelling) as well as from the Madagascan coast (advection) is shown to influence the simulated bloom. A Lagrangian experiment shows dispersion of higher percentages of particles in the bloom region during bloom years and south of Madagascar during non-bloom years. Mesoscale eddies, originating close to Australia and which propagate westward towards southern Africa, can potentially impact the South-East Madagascar Bloom. In this study, a vast majority of these features have been shown to be subsurface-intensified eddies. A co-located eddy tracking dataset with Argo profiling floats are used to devise a subsurface-eddy identification method, which is based on the steric dynamic height anomaly of a specific eddy. Adding to the `eddy-zoo', these eddies are termed `SIDDIES' (South Indian ocean eDDIES), occurring as surface (surfSIDDIES) and subsurface (subSIDDIES) features. They travel along the latitudinal band range of 15°S to 35°S which we name the ‘SIDDIES corridor’. Advecting warm and fresh water during their propagation, cyclonic (anticyclonic) subSIDDIES contribute about 58% (32%) of the total eddy-heat flux in the South Indian Ocean. Anticyclonic subSIDDIES have also been found to be the sole, high-saline water eddy-conveyor towards the western South Indian Ocean. These eddies could also possibly transport nutrients throughout their journey, impacting the biogeochemistry of the ocean near Madagascar."],"dc:identifier.uri":["http://hdl.handle.net/11427/29265"],"dc:language.iso":["eng"],"dc:publisher.department":["Department of Oceanography"],"dc:publisher.institution":["University of Cape Town"],"dc:title":["The biophysical processes controlling the South-East Madagascar Bloom"],"dc:type":["Doctoral Thesis"],"dc:type.qualificationlevel":["Doctoral"],"dc:type.qualificationname":["PhD"]},"updated_at":"2026-07-22T22:22:38Z"}