The biophysical processes controlling the South-east Madagascar Phytoplankton Bloom

Abstract : Using observational datasets and a high resolution coupled biophysical model (CROCOPISCES), the main aims of this thesis is to study the biophysical processes associated with one of the largest phytoplankton blooms in global ocean, southeast of Madagascar, and the possible role of mesoscale eddies.The study has shown that the bloom occurs in a region of shallow-stratified mixed layer water, with low-salinity waters at the surface possibly associated with the South-East Madagasacar Current (SEMC), and dipole structure in the mean circulation. Observations show that curren-driven upwelling south of Madagascar is reduced during bloom months. It is shown in the model that nitrate from subsurface levels (upwelling) as well as from the Madagascan coast (advection) fertilize the simulated bloom. A Lagrangian analysis shows dispersion of higher percentages of particles in the bloom region during bloom years and south of Madagascar during non-bloom years.Using co-located Argo profiles and an eddy detected algorithm dataset, surface and subsurface-intensified eddies are studied. Subsurface eddies are identified using a detection method based on their steric dynamic height anomaly. Referred to as `SIDDIES’ (South Indian ocean eDDIES), they occur as surface (surfSIDDIES) or subsurface (subSIDDIES) and propagate along a latitudinal band (15°S-35°S) termed as `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.
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Ahmad Fehmi Dilmahamod. The biophysical processes controlling the South-east Madagascar Phytoplankton Bloom. Earth Sciences. Université de Bretagne occidentale - Brest, 2018. English. ⟨NNT : 2018BRES0022⟩. ⟨tel-01881872⟩

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