Variations in Remotely-Sensed Phytoplankton Size Structure of a Cyclonic Eddy in the Southwest Indian Ocean

Phytoplankton size classes were derived from weekly-averaged MODIS Aqua chlorophyll a data over the southwest Indian Ocean in order to assess changes in surface phytoplankton community structure within a cyclonic eddy as it propagated across the Mozambique Basin in 2013. Satellite altimetry was used to identify and track the southwesterly movement of the eddy from its origin off Madagascar in mid-June until mid-October, when it eventually merged with the Agulhas Current along the east coast of South Africa. Nano- and picophytoplankton comprised most of the community in the early phase of the eddy development in June, but nanophytoplankton then dominated in austral winter (July and August). Microphytoplankton was entrained into the eddy by horizontal advection from the southern Madagascar shelf, increasing the proportion of microphytoplankton to 23% when the chlorophyll a levels reached a peak of 0.36 mg·m−3 in the third week of July. Chlorophyll a levels declined to 50% of the population. As far as is known, this is the first study to investigate temporal changes in chlorophyll a and community structure in a cyclonic eddy propagating across an ocean basin in the southwest Indian Ocean.

[1]  Björn C. Backeberg,et al.  Eddy properties in the Mozambique Channel: A comparison between observations and two numerical ocean circulation models , 2014 .

[2]  E. Boss,et al.  Underway spectrophotometry along the Atlantic Meridional Transect reveals high performance in satellite chlorophyll retrievals , 2016 .

[3]  H. M. van Aken,et al.  Observations of the southern East Madagascar Current and undercurrent and countercurrent system , 2008 .

[4]  Graham D. Quartly,et al.  Eddies in the southern Mozambique Channel , 2004 .

[5]  P. Brickley,et al.  Impact of Haida Eddies on chlorophyll distribution in the Eastern Gulf of Alaska , 2005 .

[6]  Trevor Platt,et al.  A three component classification of phytoplankton absorption spectra: Application to ocean-color data , 2011 .

[7]  William R. Crawford,et al.  The influence of coastal origin eddies on oceanic plankton distributions in the eastern Gulf of Alaska , 2005 .

[8]  Björn C. Backeberg,et al.  Observed eddy dissipation in the Agulhas Current , 2016 .

[9]  F. Marsac,et al.  Patterns of variability of sea surface chlorophyll in the Mozambique Channel: A quantitative approach , 2009 .

[10]  Tarron Lamont,et al.  Phytoplankton communities and acclimation in a cyclonic eddy in the southwest Indian Ocean , 2017 .

[11]  Laurent Bertino,et al.  The greater Agulhas Current system: An integrated study of its mesoscale variability , 2008 .

[12]  D. Chelton,et al.  Global observations of nonlinear mesoscale eddies , 2011 .

[13]  Tarron Lamont,et al.  Adaptation of phytoplankton communities to mesoscale eddies in the Mozambique Channel , 2014 .

[14]  Johann R. E. Lutjeharms,et al.  Eddies and dipoles around South Madagascar: formation, pathways and large-scale impact , 2004 .

[15]  Tommy D. Dickey,et al.  The transient oasis: Nutrient-phytoplankton dynamics and particle export in Hawaiian lee cyclones , 2008 .

[16]  Frédéric Ménard,et al.  Ecosystem functioning in the Mozambique Channel: Synthesis and future research , 2014 .

[17]  T. Platt,et al.  Remote sensing of phytoplankton pigments: A comparison of empirical and theoretical approaches , 2001 .

[18]  Shuibo Hu,et al.  Satellite-observed variability of phytoplankton size classes associated with a cold eddy in the South China Sea. , 2014, Marine pollution bulletin.

[19]  S. Sathyendranath,et al.  A three-component model of phytoplankton size class for the Atlantic Ocean , 2010 .

[20]  Robert J. W. Brewin,et al.  Influence of light in the mixed-layer on the parameters of a three-component model of phytoplankton size class , 2015 .

[21]  S. Sathyendranath,et al.  The influence of the Indian Ocean Dipole on interannual variations in phytoplankton size structure as revealed by Earth Observation , 2012 .

[22]  W. D. Ruijter,et al.  Dipoles of the South East Madagascar Current , 2013 .

[23]  Mathieu Rouault,et al.  Structure and origin of the subtropical South Indian Ocean Countercurrent , 2006 .

[24]  Tarron Lamont,et al.  Contrasting hydrography and phytoplankton distribution in the upper layers of cyclonic eddies in the Mozambique Basin and Mozambique Channel , 2017 .

[25]  William R. Crawford,et al.  Currents in Haida Eddies , 2005 .

[26]  R. Bidigare,et al.  Physical dynamics and biological implications of a mesoscale eddy in the lee of Hawai'i : Cyclone Opal observations during E-Flux III , 2008 .

[27]  Paul G. Falkowski,et al.  Photosynthetic community responses to upwelling in mesoscale eddies in the subtropical North Atlantic and Pacific Oceans , 2008 .

[28]  Russ E. Davis,et al.  Flow at intermediate depths around Madagascar based on ALACE float trajectories , 2003 .

[29]  H. Claustre,et al.  Vertical distribution of phytoplankton communities in open ocean: An assessment based on surface chlorophyll , 2006 .

[30]  P. J. Werdell,et al.  A multi-sensor approach for the on-orbit validation of ocean color satellite data products , 2006 .

[31]  Arne Biastoch,et al.  Modes of the southern extension of the East Madagascar Current , 2009 .

[32]  Robert R. Bidigare,et al.  Diatoms in the desert: Plankton community response to a mesoscale eddy in the subtropical North Pacific , 2008 .

[33]  Mathijs W. Schouten,et al.  Variability of the southwest Indian Ocean , 2005, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[34]  Graham D. Quartly,et al.  Eddies around Madagascar — The retroflection re-considered , 2006 .

[35]  John C. Swallow,et al.  The boundary currents east and north of Madagascar: 1. Geostrophic currents and transports , 1988 .

[36]  J. Ras,et al.  Validation of MERIS reflectance and chlorophyll during the BENCAL cruise October 2002: preliminary validation of new demonstration products for phytoplankton functional types and photosynthetic parameters , 2007 .

[37]  Pierrick Penven,et al.  Mesoscale eddy variability in the southern extension of the East Madagascar Current: Seasonal cycle, energy conversion terms, and eddy mean properties , 2014 .

[38]  Robert J. W. Brewin,et al.  Seasonal variation in remotely-sensed phytoplankton size structure around southern Africa , 2018 .

[39]  Trevor Platt,et al.  Seasonal pigment patterns of surface phytoplankton in the subtropical southern hemisphere , 2007 .

[40]  L. Beal,et al.  On the role of the Agulhas system in ocean circulation and climate , 2011, Nature.

[41]  Tarron Lamont,et al.  Characterisation of mesoscale features and phytoplankton variability in the Mozambique Channel , 2014 .