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Deep Sea Research Part I: Oceanographic Research Papers 57, 4 (2010) 567-576
Revisiting the La Nina 1998 phytoplankton blooms in the equatorial Pacific
Thomas Gorgues ( ) 1, Christophe E. Menkès 2, Lia Slemons 3, Olivier Aumont 1, Yves Dandonneau 2, Marie-Hélène Radenac 4, Séverine Alvain 5, Cyril Moulin 5

A biogeochemical model of the tropical Pacific has been used to assess the impact of interannual variability in a western Pacific iron source on the iron-limited ecosystem of the central and eastern Pacific during the 1997-1998 El Nino A reference simulation and two simulations with an iron source in the western Pacific have been performed The two "source" simulations differed only in the temporal variability of the iron source. In the variable source simulation, the iron concentration in the source region was proportional to the velocity of the New Guinea Coastal Undercurrent (NGCUC) In the constant source simulation, the same time-averaged concentration of iron was imposed with no temporal variability. The variable source was designed to mimic variations of iron flux from the northeast slope of New Guinea to the NGCUC due to modulation of sedimentary iron resuspension as previously hypothesized Through the comparison of these simulations, it appeared that: (i) an iron source in the NGCUC, regardless of its source variability, increases biomass in the eastern equatorial Pacific because of the greater eastward iron flux by the Equatorial Undercurrent and (ii) a variable NGCUC iron source does not change the temporal variability of eastern Pacific chlorophyll, and in particular the timing and intensity of the June 1998 bloom To explain eastern Pacific biological variability, local rather than remote processes are needed, such as wind-driven upwelling, the local depth of the thermocline. tropical instability waves and biological processes such as high grazing pressure. Therefore, while the western Pacific sources of dissolved iron are important in our model to sustain annually integrated equatorial Pacific production, they are unlikely to strongly constrain the timing of blooms in the central and eastern Pacific such as during the 1998 La Nina
1 :  Laboratoire de physique des océans (LPO)
CNRS : UMR6523 – Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER) – INSU – Université de Bretagne Occidentale (UBO) – Institut de recherche pour le développement [IRD] – Institut Universitaire Européen de la Mer (IUEM)
2 :  Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN)
Institut de recherche pour le développement [IRD] – INSU – CNRS : UMR7159 – Université Pierre et Marie Curie (UPMC) - Paris VI – Muséum National d'Histoire Naturelle (MNHN)
3 :  School of Oceanography (JISAO)
University of Washington
4 :  Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS)
CNRS : UMR5566 – Institut de recherche pour le développement [IRD] – CNES – Observatoire Midi-Pyrénées – INSU – Université Paul Sabatier (UPS) - Toulouse III
5 :  Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE - UMR 8212)
CNRS : UMR8212 – CEA : DSM/LSCE – Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)
Planète et Univers/Sciences de la Terre/Océanographie
La Niña – ENSO – Equatorial Pacific – Phytoplankton – Blooms – 1997-1998 – Iron – Model