%0 Journal Article
%T Indian Ocean Dipole and El Ni o/Southern Oscillation impacts on regional chlorophyll anomalies in the Indian Ocean
%A J. C. Currie
%A M. Lengaigne
%A J. Vialard
%A D. M. Kaplan
%J Biogeosciences Discussions
%D 2013
%I Copernicus Publications
%R 10.5194/bgd-10-5841-2013
%X The Indian Ocean Dipole (IOD) and the El Ni o-Southern Oscillation (ENSO) frequently co-occur, driving significant interannual changes within the Indian Ocean. We use a four-decade hindcast from a coupled bio-physical ocean general circulation model, to disentangle patterns of chlorophyll anomalies driven by these two climate modes. Comparisons with remotely-sensed records show that the simulation competently reproduces the chlorophyll seasonal cycle, as well as open-ocean anomalies during the 1997¨C1998 ENSO and IOD event. Results show that anomalous surface and euphotic-layer chlorophyll blooms in the eastern equatorial Indian Ocean in fall, and southern Bay of Bengal in winter, are primarily related to IOD forcing. IOD depresses integrated chlorophyll in the 5¡ã S¨C10¡ã S thermocline ridge region, even though the signal is negligible in surface chlorophyll. A previously-unreported negative influence of IOD on chlorophyll concentrations is also shown in a region around the southern tip of India. The only investigated region where ENSO has a greater influence on chlorophyll than does IOD, is in the Somalia upwelling region, where it causes a decrease in fall and winter chlorophyll by reducing local upwelling winds. Lastly, we show that the chlorophyll impact of climate indices is frequently asymmetric, with a general tendency for larger positive than negative chlorophyll anomalies. ENSO and IOD cause significant and predictable regional re-organisation of phytoplankton productivity via their influence on near-surface oceanography. Resolving the details of these effects should improve our understanding, and eventually gain predictability, of interannual changes in Indian Ocean productivity, fisheries, ecosystems and carbon budgets.
%U http://www.biogeosciences-discuss.net/10/5841/2013/bgd-10-5841-2013.pdf