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Wintertime Phytoplankton Blooms in the Western Equatorial Indian Ocean Associated With the Madden‐Julian Oscillation
Author(s) -
Liao Xiaomei,
Du Yan,
Zhan Haigang,
Wang Tianyu,
Feng Ming
Publication year - 2017
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2017jc013203
Subject(s) - thermocline , madden–julian oscillation , equator , oceanography , upwelling , climatology , phytoplankton , environmental science , mixed layer , monsoon , argo , sea surface temperature , geology , atmospheric sciences , nutrient , latitude , geography , convection , meteorology , chemistry , geodesy , organic chemistry
This study investigated boreal wintertime phytoplankton blooms in the western equatorial Indian Ocean (WEIO) and the underlying physical mechanisms. The Sea viewing Wide field of View sensor (SeaWiFS) chlorophyll‐ a (Chl a ) concentrations show that phytoplankton blooms occur in the WEIO during December–March. The development of these blooms is not only a seasonal process but also consists of 2–3 intraseasonal events induced by the Madden‐Julian Oscillation (MJO). During a typical intraseasonal event, enhanced cross‐equatorial wind induces strong upwelling and ocean mixing, thus increasing the supply of nutrients to the surface in equatorial regions. Argo profiles clearly show various responses to the intraseasonal wind bursts, including shoaling of the thermocline and deepening of the mixed layer. Further analysis reveals that the former is the dominant mechanism for the blooms along the equator, while the latter controls the high Chl a concentrations off the coast of Somalia. Surface ocean circulations not only account for the blooms south of the equator but also modulate the thermocline depth in the WEIO. The shallower thermocline during the early period of the northeast monsoon season provides favorable conditions for a stronger Chl a response to intraseasonal forcing.