Variability of upwelling and chlorophyll in the equatorial Atlantic
Open accessAbstract
The primary seasonal phytoplankton bloom in the equatorial Atlantic occurs in boreal summer in response to seasonal strengthening of zonal winds. However, the equatorial Atlantic also has a secondary bloom in late fall – early winter. This secondary bloom is weaker than the primary bloom by a factor of two, but is subject to year‐to‐year variability that is similar in magnitude. Here, observational evidence, including sea level and SeaWiFS‐derived chlorophyll‐a concentration, is used to examine several potential causes of this secondary bloom. The secondary bloom varies independently of blooms along the eastern coastal zones. Also, the secondary bloom has a relationship with the cessation of the Northwest African monsoon, which propotes the secondary seasonal strengthening of the trade winds. The variability of the secondary bloom results from perturbations in the depth of the thermocline induced by zonal wind anomalies in the western tropical Atlantic. These wind anomalies are correlated with mean sea level atmospheric pressure anomalies in the region of the northern subtropical high as well as over the Amazon.
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Strong similarities between the seasonal cycle of chlorophyll and the seasonal cycle of sea surface temperature suggest that the same physical processes could control the supply of cool and nutrient-rich waters into the euphotic layer.
“Strong similarities between this seasonal cycle and the seasonal cycle of sea surface temperature (SST) suggest that the same physical processes could control the supply of cool and nutrient-rich waters into the euphotic layer (Hisard, 1973;Oudot and Morin, 1987;Grodsky et al., 2008;Jouanno et al., 2011a).”
From Physical drivers of the nitrate seasonal variability in the Atlantic cold tongue (2020) · cites this paper as Grodsky et al., 2008
A semiannual cycle of surface chlorophyll exists in the Atlantic cold tongue, with a primary bloom in July-August between 20°W and 5°W and a shorter, weaker secondary bloom in December.
“Ocean color observations show semiannual variations of chlorophyll in the Atlantic cold tongue with a main bloom in boreal summer and a secondary bloom in December.”
From Physical drivers of the nitrate seasonal variability in the Atlantic cold tongue (2020) · cites this paper as Grodsky et al., 2008
Central equatorial mixed layer nitrate variability does not seem to be directly connected with mixed layer nitrate input along the African coast.
“This central equatorial variability does not seem to be directly connected with mixed layer nitrate input along the African coast, in agreement with the chlorophyll behavior in the equatorial Atlantic deduced from satellite data (Grodsky et al., 2008).”
From Physical drivers of the nitrate seasonal variability in the Atlantic cold tongue (2020) · cites this paper as Grodsky et al., 2008
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Research works printed but not linked: 5
- Liu, W. T. (2002), Progress in scatterometer application, J. Oceanogr., 58(1), 121 -136.
- Monger, B., C. McClain, and R. Murtugudde (1997), Seasonal phytoplank- ton dynamics in the eastern tropical Atlantic, J. Geophys. Res., 102, 12,389 -12,412, doi:10.1029/96JC03982. · DOI · Paper page
- Perez, V., E. Fernandez, E. Maranon, P. Serret, and C. Garcia-Soto (2005), Seasonal and interannual variability of chlorophyll-a and primary produc- tion in the Equatorial Atlantic: In situ and remote sensing observations, J. Plankton Res., 27(2), 189 -197.
- Schott, F. A., J. P. McCreary, and G. C. Johnson (2004), Shallow over- turning circulation of the tropical-subtropical oceans, in Earth Climate: The Ocean-Atmosphere Interaction, Geophys. Monogr. Ser., vol. 147, pp. 261 -304, AGU, Washington, D. C. Schouten, M. W., R. P. Matano, and T. P. Strub (2005), A description of the seasonal cycle of the equatorial Atlantic from altimeter data, Deep Sea Res., Part I, 52, 477 -493.
- Signorini, S. R., R. G. Murtugudde, C. R. McClain, J. R. Christian, J. Picaut, and A. J. Busalacchi (1999), Biological and physical signatures in the tropical and subtropical Atlantic, J. Geophys. Res., 104, 18,367 -18,382, doi:10.1029/1999JC900134. · DOI · Paper page
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The tropical atlantic observing system
Foltz, G. R., Brandt, P., Richter, I., Rodríguez-Fonseca, B., Hernandez, F., Dengler, M., Rodrigues, R. R., Schmidt, J. O., Yu, L., Lefevre, N., et al. (2019) · Frontiers in Marine Science · doi:10.3389/fmars.2019.00206 · Cited by 150 · see citing works
Self-citationPhysical drivers of the nitrate seasonal variability in the Atlantic cold tongue
Radenac, M.-H., Jouanno, J., Tchamabi, C. C., Awo, M., Bourlès, B., Arnault, S., & Aumont, O. (2020) · Biogeosciences · doi:10.5194/bg-17-529-2020 · Cited by 33 · see citing works
- Authors
- Grodsky, S. A., Carton, J. A., & McClain, C. R.
- Affiliations
- University of Maryland, College Park (US)
- Goddard Space Flight Center (US)
- Venue
- Geophysical Research Letters
- Publisher
- American Geophysical Union (AGU)
- Published
- 2008-02
- Volume
- 35
- Issue
- 3
- ISSN
- 0094-8276 (ISSN-L)
- 1944-8007
- OpenAlex
- W2088393010
- Cited by
- 67
- References
- 0
- Citations by year
- 2026: 5 · 2025: 3 · 2024: 3 · 2023: 12 · 2022: 5 · 2021: 4 · 2020: 5 · 2019: 6 · 2018: 3 · 2017: 3 · 2016: 2 · 2015: 3 · 2014: 1 · 2013: 2 · 2012: 4
- FWCI
- 1.39
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- Geophysical Research Letters (publishedVersion)
- Topics
- Physical Sciences › Earth and Planetary Sciences › Oceanography › Marine and coastal ecosystems
- Physical Sciences › Earth and Planetary Sciences › Oceanography › Oceanographic and Atmospheric Processes
- Physical Sciences › Environmental Science › Global and Planetary Change › Climate variability and models
- Keywords
- equatorial Atlantic, upwelling, chlorophyll-a variability, trade winds, thermocline depth, zonal wind anomalies, sea level pressure anomalies, Amazon, seasonal phytoplankton blooms
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