A New Definition of the South‐East Madagascar Bloom and Analysis of Its Variability.

Dilmahamod, A. Fehmi , Penven, P. , Aguiar‐González, B. , Reason, C. J. C. and Hermes, J. C. (2019) A New Definition of the South‐East Madagascar Bloom and Analysis of Its Variability. Open Access Journal of Geophysical Research: Oceans, 124 (3). pp. 1717-1735. DOI 10.1029/2018JC014582.

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Abstract

The South-East Madagascar Bloom occurs in an oligotrophic region of the southwest Indian Ocean. Phase locked to austral summer, this sporadic feature exhibits substantial temporal and spatial variability. Several studies, with different hypotheses, have focused on the initiation mechanism triggering the bloom, but none has been as yet clearly substantiated. With 19 years of ocean color data set available as well as in situ measurements (Argo profiles), the time is ripe to review this feature. The bloom is characterized in a novel manner, and a new bloom index is suggested, yielding 11 bloom years, including 3 major bloom years (1999, 2006, and 2008). Spatially, the bloom varies from a mean structure (22–32°S; 50–70°E) both zonally and meridionally. A colocation analysis of Argo profiles and chlorophyll-a data revealed a bloom occurrence in a shallow-stratified layer, with low-salinity water in the surface layers. Additionally, a quantitative assessment of the previous hypotheses is performed and bloom occurrence is found to coincide with La Niña events and reduced upwelling intensity south of Madagascar. A stronger South-East Madagascar Current during La Niña may support a detachment of the current from the coasts, dampening the upwelling south of Madagascar, and feeding low-salinity waters into the Madagascar Basin, hence increasing stratification. Along with abundance of light, these provide the right conditions for a nitrogen-fixing cyanobacterial phytoplankton bloom onset

Document Type: Article
Keywords: South-East Madagascar Bloom; South-East Madagascar Current; La Nina; cyanobacterial bloom
Research affiliation: IFREMER
OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-PO Physical Oceanography
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1029/2018JC014582
ISSN: 2169-9275
Date Deposited: 01 Apr 2019 12:59
Last Modified: 16 Sep 2019 23:38
URI: http://oceanrep.geomar.de/id/eprint/46254

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