Coastal trapped waves and tidal mixing control primary production in the tropical Angolan upwelling system

Mareike Körner (1) , Peter Brandt (2) , Serena Illig (3, 4) , Marcus Dengler (1) , Ajit Subramaniam (5) , Marie-Lou Bachèlery (6) , Gerd Krahmann (1)

1 GEOMAR - Helmholtz Centre for Ocean Research [Kiel]
2 CAU - Christian-Albrechts-Universität zu Kiel = Christian-Albrechts University of Kiel = Université Christian-Albrechts de Kiel
3 LEGOS - Laboratoire d'études en Géophysique et océanographie spatiales
4 UCT-OD - Oceanography Department
5 Columbia University [New York]
6 UiB - Geophysical Institute, University of Bergen and Bjerknes Centre for Climate Research

Eastern boundary upwelling systems are hotspots of marine life and primary production. The strength and seasonality of upwelling in these systems are usually related to local wind forcing. However, in some tropical upwelling systems, seasonal maxima of productivity occur when upwelling favorable winds are weak. Here, we show that in the tropical Angolan upwelling system (tAUS), the seasonal productivity maximum is due to the combined effect of coastal trapped waves (CTWs) and elevated tidal mixing on the shelf. During austral winter, the passage of an upwelling CTW displaces the nitracline upward by more than 50 m. Thereby, nitrate-rich waters spread onto the shelf, where elevated vertical mixing causes a nitrate flux into the surface mixed layer. Interannual variability of the productivity maximum is strongly correlated to the amplitude of the upwelling CTW as seen in sea level data. Given that CTWs are connected to equatorial forcing, a predictability of the strength of the productivity maximum is suggested.

Domains: Ocean, Atmosphere

Mareike Körner, Peter Brandt, Serena Illig, Marcus Dengler, Ajit Subramaniam, et al.. Coastal trapped waves and tidal mixing control primary production in the tropical Angolan upwelling system. Science Advances , 2024, 10 (4), ⟨10.1126/sciadv.adj6686⟩. ⟨ird-04559059⟩