Articles | Volume 22, issue 2
https://doi.org/10.5194/os-22-1279-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/os-22-1279-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
22 Apr 2026
Research article |
| 22 Apr 2026
| 22 Apr 2026
Physical and biological processes driving seasonal variability of Nitrate budget and biological productivity in the Gabon-Congo upwelling system
Landry Junior Mbang Essome
CORRESPONDING AUTHOR
Université de Toulouse, LEGOS (CNES/CNRS/IRD/UT), Toulouse, France
Laboratoire de Géosciences, de l'Environnement et Applications, Université Nationale des Sciences Technologies, Ingénierie et Mathématiques, Abomey, Benin
Gaël Alory
Université de Toulouse, LEGOS (CNES/CNRS/IRD/UT), Toulouse, France
Casimir Yelognissé Da-Allada
Laboratoire de Géosciences, de l'Environnement et Applications, Université Nationale des Sciences Technologies, Ingénierie et Mathématiques, Abomey, Benin
Department of Oceanography and Applications, International Chair in Mathematical Physics and Applications, University of Abomey-Calavi, Cotonou, Benin
Laboratoire d'Hydrologie Marine et Côtière, Institut de Recherches Halieutiques et Océanologiques du Bénin, Cotonou, Benin
Isabelle Dadou
Université de Toulouse, LEGOS (CNES/CNRS/IRD/UT), Toulouse, France
Roy Dorgeless Ngakala
Department of Oceanography and Applications, International Chair in Mathematical Physics and Applications, University of Abomey-Calavi, Cotonou, Benin
Department of Oceanography and Environment, Institut National de Recherche en Sciences Exactes et Naturelles, Pointe-Noire, Congo
Guillaume Morvan
Université de Toulouse, LEGOS (CNES/CNRS/IRD/UT), Toulouse, France
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Amine M'hamdi, Ariane Koch-Larrouy, Anthony Bosse, Isabelle Dadou, Vincent Vantrepotte, and Alex Costa da Silva
EGUsphere, https://doi.org/10.5194/egusphere-2026-4862, https://doi.org/10.5194/egusphere-2026-4862, 2026
This preprint is open for discussion and under review for Ocean Science (OS).
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Internal tides are underwater waves that can transport nutrients from deep waters toward the sunlit ocean. Using glider observations off the Amazon shelf, we compared vertical advection and turbulent mixing. Vertical advection supplied more nitrate and silicate on average, while turbulence became important during energetic events. Together, these processes change nutrient supply and balance, potentially influencing phytoplankton communities in the tropical Atlantic.
Philippe Gamet, Bimal K. Bhattacharya, Jean-Louis Roujean, Gilles Boulet, Corinne Salcedo, Albert Olioso, Kanishka Mallick, Marie Weiss, Emmanuelle Sarrazin, Emmanuelle Autret, Laure Roupioz, José Antonio Sobrino, Olivier Merlin, Ghislain Picard, Thomas H. G. Vidal, Mark Irvine, Rahul Nigam, Mehul Pandya, Simon Gascoin, Sébastien Marcq, Manoj K. Mishra, Emilie Delogu, Vincent Rivalland, Jordi Etchanchu, Jean-Louis Raynaud, Meenakshi Sarkar, Rishi K. Gangwar, Sushil K. Singh, Renaud Binet, Sara Arioli, Hervé Yésou, Isabelle Dadou, Alexei Kouraev, Julien Michel, Benoit Coudert, Samuel Mwangi, Nesrine Farhani, Ayan Das, Stéphane Saux-Picart, Thierry Tormos, Jean-François Piollé, Charles Verpoorter, Auline Rodler, Jonathan Leon Tavares, Jennifer Adams, Anand S. Sahadevan, Besavaraju Santhi Sree, Manikumar Vedantam, Dheeraj Adlakha, Laurence Buffet, Kathrin Naegeli, Itziar Barat, Jerome Demarty, Olivier Hagolle, and Philippe Maisongrande
EGUsphere, https://doi.org/10.5194/egusphere-2026-4492, https://doi.org/10.5194/egusphere-2026-4492, 2026
This preprint is open for discussion and under review for Earth Observation (EO).
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This paper highlights how the upcoming TRISHNA satellite mission (launching 2027) will transform Earth observation by providing high-resolution (60 m) thermal infrared imagery with sub-weekly revisits. It details the mission's design and its synergies with other future missions to significantly improve the monitoring of global surface temperature and its dynamics, water stress, and ecosystem energy processes.
Perrine Bauchot, Ariane Koch-Larrouy, Michel Tchilibou, Loren Carrère, Fabrice Hernandez, Guillaume Morvan, and Jérôme Chanut
Ocean Sci., 22, 2011–2025, https://doi.org/10.5194/os-22-2011-2026, https://doi.org/10.5194/os-22-2011-2026, 2026
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The Vitória–Trindade Ridge off the Brazilian coast is a hotspot for internal tides, which drive energy and nutrients exchanges in the ocean. Using satellite data and a high-resolution ocean model, we study what influences these small waves in this region. We show that internal tides are generated more strongly in summer and lose energy faster in winter. Ocean eddies may also affect their fate. These results are essential for understanding oceanic energy pathways and refine model predictions.
Amine M'hamdi, Ariane Koch-Larrouy, Isabelle Dadou, Carina Regina de Macedo, Fernand Assene, Vincent Vantrepotte, Guillaume Morvan, and Alex Costa da Silva
EGUsphere, https://doi.org/10.5194/egusphere-2026-2729, https://doi.org/10.5194/egusphere-2026-2729, 2026
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We show that tides play a major role in structuring nutrient supply and phytoplankton variability across the Amazon shelf–offshore continuum, from the 15-day spring–neap cycle to seasonal timescales. By enhancing nitrate uplift, especially along the shelf break and internal-tide pathway, tides stimulate offshore chlorophyll growth, modulate the nitracline and deep chlorophyll maximum, and explain a large fraction of the seasonal nutrient signal.
Fabius Kouogang, Ariane Koch-Larrouy, Xavier Carton, Fernand Assene, Guillaume Morvan, and Moacyr Araujo
Ocean Sci., 22, 1545–1568, https://doi.org/10.5194/os-22-1545-2026, https://doi.org/10.5194/os-22-1545-2026, 2026
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Our research investigates how large waves travel deep within the ocean. Using a detailed computer model, we show that when these deep waves meet giant ocean circulation, their path is dramatically changed. They can be bent off course, split apart, or stopped completely. An underwater mountain works with this circulation to transfer the wave energy between different ocean layers. Understanding this process is vital because it controls ocean mixing.
Carina Regina de Macedo, Ariane Koch-Larrouy, José Carlos Bastos da Silva, Jorge Manuel Magalhães, Fernand Assene, Manh Duy Tran, Isabelle Dadou, Amine M'Hamdi, Trung Kien Tran, and Vincent Vantrepotte
Ocean Sci., 22, 871–892, https://doi.org/10.5194/os-22-871-2026, https://doi.org/10.5194/os-22-871-2026, 2026
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We investigated how ocean tides influence marine phytoplankton along the North Brazilian coast. Using satellite data from 2005 to 2021, we found that tides can either enhance or reduce phytoplankton growth on the continental shelf. Offshore, internal tides stimulate primary production along their pathways. These results improve our understanding of how tidal processes shape marine life in tropical coastal regions.
Chloé Goret, Ariane Koch-Larrouy, Fabius Kouogang, Carina Regina de Macedo, Amine M'Hamdi, Jorge M. Magalhães, José Carlos Bastos da Silva, Michel Tchilibou, Camila Artana, Isabelle Dadou, Antoine Delepoulle, Simon Barbot, Maxime Ballarotta, Loren Carrère, and Alex Costa da Silva
Ocean Sci., 22, 679–698, https://doi.org/10.5194/os-22-679-2026, https://doi.org/10.5194/os-22-679-2026, 2026
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Using high-resolution satellite measurements, we observed how eddies off the Amazon shelf modify internal solitary waves. The results show that these waves can be deflected from their path, even split into two branches, and change their geometry when interacting with different types of eddies. This work provides new insight into the ocean’s complex dynamic interactions and could help guide future predictions of ocean behavior and its effects on coastal and marine ecosystems.
Fernand Assene, Ariane Koch-Larrouy, Carina Regina de Macedo, Isabelle Dadou, Michel Tchilibou, Guillaume Morvan, Damien Allain, Simon Barbot, Alex Costa da Silva, Jérôme Chanut, Vincent Vantrepotte, Florent Lyard, Edward Zaron, and Trung-Kien Tran
EGUsphere, https://doi.org/10.5194/egusphere-2026-557, https://doi.org/10.5194/egusphere-2026-557, 2026
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We examine temperature (T) variability at two semidiurnal and one fortnightly frequencies in North Brazil using satellite-observed and modeled temperatures. Semidiurnal T variability is weak offshore but peaks over the shelf due to barotropic mixing. Below 100 m, internal tide (IT)-driven mixing causes strong T variability (0.6–2 °C). T fortnightly maximums (~0.15 °C) appear along IT pathways, showing their key role.
Amine M'hamdi, Ariane Koch-Larrouy, Alex Costa da Silva, Isabelle Dadou, Carina Regina de Macedo, Anthony Bosse, Vincent Vantrepotte, Habib Micaël Aguedjou, Trung-Kien Tran, Pierre Testor, Laurent Mortier, Arnaud Bertrand, Pedro Augusto Mendes de Castro Melo, James Lee, Marcelo Rollnic, and Moacyr Araujo
Ocean Sci., 21, 2873–2894, https://doi.org/10.5194/os-21-2873-2025, https://doi.org/10.5194/os-21-2873-2025, 2025
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In the ocean off the Amazon shelf, internal waves caused by tides move water layers up and down and mix them. Using an underwater glider and satellites, we found internal tides redistribute chlorophyll from the deep chlorophyll maximum upward to the surface and downward to depth. Turbulent chlorophyll fluxes supply about 38 % of surface chlorophyll, and total chlorophyll increases by 14–29 % during strong tides, potentially affecting the marine food web.
Fernand Assene, Ariane Koch-Larrouy, Isabelle Dadou, Michel Tchilibou, Guillaume Morvan, Jérôme Chanut, Alex Costa da Silva, Vincent Vantrepotte, Damien Allain, and Trung-Kien Tran
Ocean Sci., 20, 43–67, https://doi.org/10.5194/os-20-43-2024, https://doi.org/10.5194/os-20-43-2024, 2024
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Twin simulations, with and without tides, are used to assess the impact of internal tides (ITs) on ocean temperature off the Amazon mouth at a seasonal scale. We found that in the surface layers, ITs and barotropic tides cause a cooling effect on sea surface temperature, subsequently leading to an increase in the net heat flux between the atmosphere and ocean. Vertical mixing is identified as the primary driver, followed by vertical and horizontal advection.
Peter Brandt, Gaël Alory, Founi Mesmin Awo, Marcus Dengler, Sandrine Djakouré, Rodrigue Anicet Imbol Koungue, Julien Jouanno, Mareike Körner, Marisa Roch, and Mathieu Rouault
Ocean Sci., 19, 581–601, https://doi.org/10.5194/os-19-581-2023, https://doi.org/10.5194/os-19-581-2023, 2023
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Tropical upwelling systems are among the most productive ecosystems globally. The tropical Atlantic upwelling undergoes a strong seasonal cycle that is forced by the wind. Local wind-driven upwelling and remote effects, particularly via the propagation of equatorial and coastal trapped waves, lead to an upward and downward movement of the nitracline. Turbulent mixing results in upward supply of nutrients. Here, we review the different physical processes responsible for biological productivity.
Roy Dorgeless Ngakala, Gaël Alory, Casimir Yélognissè Da-Allada, Olivia Estelle Kom, Julien Jouanno, Willi Rath, and Ezinvi Baloïtcha
Ocean Sci., 19, 535–558, https://doi.org/10.5194/os-19-535-2023, https://doi.org/10.5194/os-19-535-2023, 2023
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Surface heat flux is the main driver of the heat budget in the Senegal, Angola, and Benguela regions but not in the equatorial region. In the Senegal and Benguela regions, freshwater flux governs the salt budget, while in equatorial and Angola regions, oceanic processes are the main drivers. Results from numerical simulation show the important role of mesoscale advection for temperature and salinity variations in the mixed layer. Nonlinear processes unresolved by observations play a key role.
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Short summary
We used a high-resolution model to study how ocean currents and waves, especially coastal trapped waves, control nitrate variability in the Gabon-Congo upwelling system. This nutrient availability drives seasonal marine productivity, with the Congo River also adding significant nitrate. Our research clarifies the complex interplay of physical and biological factors, offering crucial insights for managing regional fisheries and assessing climate change impacts on this vital ecosystem.
We used a high-resolution model to study how ocean currents and waves, especially coastal...
