How Waves and Mixing Impact Coastal Upwelling Systems

Coastal upwelling regions along the eastern boundaries of the Atlantic and Pacific Oceans are recognized as highly productive and biodiverse areas in the world’s oceans. The movement of near-surface water away from the coast, driven by equatorward winds, leads to the upwelling of cold, nutrient-rich water from the depths. This process stimulates the growth of phytoplankton, forming the foundation for a diverse marine ecosystem in these areas.

In certain tropical areas, high productivity persists even when the winds favorable for upwelling are weak. However, an international research team has examined the physical mechanisms behind the upwelling phenomenon off the coast of Angola. Their investigation revealed that a combination of coastal trapped waves and increased mixing on the shelf governs productivity in this system. Published in the journal Science Advances, their findings have the potential to enhance the prediction of seasonal peaks in productivity.

Mareike Körner’s Insight into Angola’s Upwelling

However, Mareike Körner, a Ph.D. student in the Research Unit Physical Oceanography at the GEOMAR Helmholtz Center for Ocean Research Kiel and the corresponding author, explains, “Productivity in the upwelling region off Angola exhibits significant seasonal fluctuations, with the primary upwelling season occurring in the austral winter from July to September. This period witnesses high primary productivity off the Angolan coast, coinciding with increased fishing activities.”

The role of oceanic interior waves is crucial for productivity, as they induce the movement of cold, nutrient-rich water on seasonal time scales. These waves originate at the equator, where seasonal wind fluctuations generate waves that travel eastward along the equator.

Coastal Trapped Waves and Phytoplankton Blooms Off Angola

Upon reaching the eastern boundary of the equatorial Atlantic, these waves excite coastal trapped waves that propagate polewards along the African coast. During this journey, the coastal trapped waves carry nutrient-rich waters onto the Angolan shelf. Intense tidal mixing on the shelf brings these nutrients to the surface, triggering a phytoplankton bloom. The variability in plankton blooms depends on the intensity and arrival time of the coastal trapped waves and can fluctuate from year to year.

To conduct their research, the scientists integrated hydrographic, oxygen, nitrate, and satellite data along with a regional ocean model.

According to Körner, “The upwelling phenomenon off Angola is triggered by waves generated at the equator and subsequently traveling along the African coast. This offers the potential to forecast the intensity and timing of the biological productivity peak off Angola on a seasonal basis.”

Understanding the Dynamics of Southwest Africa’s Coastal Upwelling System

In fact, a comprehensive comprehension of the driving forces within this coastal upwelling system in southwest Africa is essential for evaluating potential future alterations, including the impacts of climate change or other human influences, in this vital marine ecosystem.

At GEOMAR, the “Upwelling in the Atlantic Ocean” is a key research focus as part of the GEOMAR 2030 strategy. Since 2013, GEOMAR has been engaged in extensive research in the region and has established significant collaborations with Angolan counterparts.

To conclude, the Research Unit Physical Oceanography has led seven research cruises, contributing extensive data on shelf nutrient distribution and mixing. Additionally, a subsurface mooring has been collecting data on various parameters, including current velocities, temperature, salinity, and oxygen, since 2013.

Read the original article on: Phys Org

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