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The Madagascar Bloom: A serendipitous study
Author(s) -
Srokosz M. A.,
Quartly G. D.
Publication year - 2013
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2012jc008339
Subject(s) - seawifs , bloom , trichodesmium , oceanography , upwelling , ocean color , iron fertilization , environmental science , phytoplankton , algal bloom , diatom , satellite , climatology , geology , biology , ecology , diazotroph , physics , nutrient , paleontology , nitrogen fixation , astronomy , bacteria
The late austral summer (February–April) phytoplankton bloom that occurs east of Madagascar exhibits significant interannual variability and at its largest extent covers ~1% of the world's ocean surface area. The bloom raises many intriguing questions about how it begins, is sustained, propagates to the east, exports carbon, and ends. It has been observed and studied using satellite ocean color observations, but the lack of in situ data makes it difficult to address these questions. Here we describe observations that were made serendipitously on a cruise in February 2005. These show clearly for the first time the simultaneous existence of a deep chlorophyll maximum at ~70–110 m depths (seen in SeaSoar fluorimeter data) and a surface chlorophyll signature [seen in Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) satellite ocean color data]. The observations also show the modulation of the biological signature at the surface by the eddy field but not of the deep chlorophyll maximum. Trichodesmium dominates the bloom nearer to Madagascar, while the diatom Rhizosolenia clevei (and its symbiont Richelia intracellularis ) dominates further from the island. The surface bloom seen in the SeaWiFS data is confined to the shallow (~30 m) mixed layer. It is hypothesized that the interannual variability in bloom intensity may be due to variations in coastal upwelling and thus the supply of iron, which is a micronutrient that can limit diazotroph growth.