Articles | Volume 22, issue 5
https://doi.org/10.5194/os-22-2973-2026
https://doi.org/10.5194/os-22-2973-2026
Research article
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30 Sep 2026
Research article | Highlight paper |  | 30 Sep 2026

Chlorophyll a concentration effects on equatorial Atlantic Ocean mean-state and interannual variability

Arthur Prigent, Riccardo Farneti, Manfredi Manizza, and Rodrigue Anicet Imbol Koungue

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Cited articles

Anderson, W. G., Gnanadesikan, A., Hallberg, R., Dunne, J., and Samuels, B. L.: Impact of ocean color on the maintenance of the Pacific Cold Tongue, Geophys. Res. Lett., 34, https://doi.org/10.1029/2007GL030100, 2007. a
Anderson, W., Gnanadesikan, A., and Wittenberg, A.: Regional impacts of ocean color on tropical Pacific variability, Ocean Sci., 5, 313–327, https://doi.org/10.5194/os-5-313-2009, 2009. a, b, c
Bjerknes, J.: ATMOSPHERIC TELECONNECTIONS FROM THE EQUATORIAL PACIFIC, Mon. Weather Rev., 97, 163–172, https://doi.org/10.1175/1520-0493(1969)097<0163:ATFTEP>2.3.CO;2, 1969. a
Brandt, P., Caniaux, G., Bourlès, B., Lazar, A., Dengler, M., Funk, A., Hormann, V., Giordani, H., and Marin, F.: Equatorial upper-ocean dynamics and their interaction with the West African monsoon, Atmos. Sci. Lett., 12, 24–30, https://doi.org/10.1002/asl.287, 2011. a
Brandt, P., Alory, G., Awo, F. M., Dengler, M., Djakouré, S., Imbol Koungue, R. A., Jouanno, J., Körner, M., Roch, M., and Rouault, M.: Physical processes and biological productivity in the upwelling regions of the tropical Atlantic, Ocean Sci., 19, 581–601, https://doi.org/10.5194/os-19-581-2023, 2023. a, b
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Editorial statement
While it is normally understood that marine biogeochemical processes strongly depend on the physical drivers, but less so in the converse, here the authors demonstrate that nonlinear responses are present in a series of experiments that modify the absorption rate of light based on chlorophyll concentrations. While the leading order mechanism is clear (more absorption, less radiative forcing on the ocean), the more detailed governing mechanisms for the oceanic response are less obvious, and the authors provide some investigations towards that end with a focus on tropical regions. They also suggest that the ongoing observed decrease in tropical Atlantic chlorophyll-a concentration may weaken the interannual variability of sea surface temperature.
Short summary
Ocean model simulations with chlorophyll-a scaled from 0.01–2× climatology show that low chlorophyll (“clear ocean”) warms the eastern equatorial Atlantic by 0.15 °C, weakens vertical temperature gradients, deepens the mixed layer, and reduces equatorial upwelling. These changes reduce the sea surface temperature (SST) seasonal cycle by 14% and interannual variability by 12.9%, suggesting that a decline in tropical Atlantic chlorophyll may weaken SST variability.
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