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|Abstract Submission No.||ABS-2022-05-0067|
|Title of Abstract||The South-East Madagascar Bloom - An observational and modeling perspective|
|Authors||Dilmahamod Ahmad Fehmi*, Pierrick Penven, Borja Aguiar-González, Chris Reason, Juliet Hermes|
Kiel, Schleswig-Holstein, Germany
|Abstract||The South-East Madagascar Bloom is one of the most compelling biogeochemical features of the Indian Ocean. A unique aspect of it is its sporadic occurrence in an oligotrophic habitat during austral summer. Using extended observational datasets, a review of the bloom indicates that it occurs within a shallow-stratified layer, with fresher water in the surface layers. A quantitative assessment of previously proposed causes revealed the co-occurrence of the bloom with La Nina events and reduced upwelling intensity south of Madagascar. A new hypothesis was advanced, which entails an early detachment of the South-East Madagascar Current during La Nina, hence feeding low-salinity nutrient-rich coastal waters into the Madagascar Basin. This hypothesis is investigated in a high-resolution biophysical model. The model is able to resolve an intermittent austral summer bloom but in the subsurface levels (0-20 m), as well as the water mass signature analogous to the observed bloom. From a nutrient flux analysis, it is shown that horizontal advection of low-salinity nutrient-rich Madagascan coastal waters can indeed trigger a phytoplankton bloom. The coupled model is also able to resolve a bloom that is atmospherically forced by cyclonic activity.|