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https://doi.org/10.5194/bg-2019-169
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-169
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 06 Jun 2019

Research article | 06 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

The influence of tropical Indian Ocean warming and Indian Ocean Dipole on the surface chlorophyll concentration in the eastern Arabian Sea

Syam Sankar1, Anoop Thondithala Ramachandran2, Kemgang Ghomsi Franck Eitel3,4, Dmitry Kondrik5, Radharani Sen6, Ramesh Madipally2, and Lasse H. Pettersson7 Syam Sankar et al.
  • 1Nansen Environmental Research Centre India (NERCI), Kochi, 68206, India
  • 2ESSO-National Centre for Earth Science Studies (ESSO-NCESS), Thiruvananthapuram, 695011, India
  • 3Department of Physics, The University of Yaoundé I, P.O. Box 812, Yaoundé, Cameroon
  • 4Nansen Scientific Society (NSS), Bergen, N-5006, Norway
  • 5Nansen International Environmental and Remote Sensing Center (NIERSC), St. Petersburg, 199034, Russia
  • 6Indian Institute of Technology (IIT), Kharagpur, 721302, India
  • 7Nansen Environmental and Remote Sensing Center (NERSC), Bergen, Norway

Abstract. This study examines the role of increased Indian Ocean warming and positive Indian Ocean Dipole (IOD) events on the surface chlorophyll concentration in the Eastern Arabian Sea (EAS) during the period 1998 to 2014. Remotely sensed surface chlorophyll concentration – during the month of October when IOD strength is maximum – at three selected areas in the EAS, viz., the central eastern Arabian Sea (CEAS, 73° E–76° E, 13° N–18° N), south eastern Arabian Sea (SEAS, 74° E–77° E, 8° N–13° N) and the southern tip of India (TIP, 74° E–78° E, 5° N–8° N) shows a steady decreasing trend, though not statistically significant. The EAS also has a higher warming trend when compared to the western basin during the study period. Our analysis has shown that in the EAS, local surface winds, remote forcing by equatorial winds and the surface and sub-surface oceanic circulation features are less (respectively more) favorable for inducing coastal upwelling during positive (respectively negative) IOD years. The Dipole Mode Index (DMI) and surface chlorophyll concentration in the EAS is significantly and negatively correlated, pointing to the fact that in the event of occurrence of frequent positive IOD years under a global warming regime, the surface chlorophyll concentration is likely to decrease during fall.

Syam Sankar et al.
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Short summary
We analyzed the role of Indian Ocean warming and positive Indian Ocean Dipole (IOD) events on the chlorophyll concentrations in the Eastern Arabian Sea (EAS). Positive IOD years were found to be less favorable for inducing coastal upwelling in the region. Significant negative correlation between positive IODs and chlorophyll concentrations show that in the event of occurrence of frequent positive IOD events under a warming regime, the chlorophyll concentration is likely to decrease during fall.
We analyzed the role of Indian Ocean warming and positive Indian Ocean Dipole (IOD) events on...
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