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Why is the ocean around the Cape Verde Islands teeming with life despite lying in one of the most nutrient-poor regions of the Atlantic? A study led by GEOMAR provides answers. By analysing two decades of interdisciplinary observational data, the researchers identified three key small-scale physical processes — eddies, internal waves and wind-driven island wakes — that drive the upward transport of nutrients to the surface. These local dynamics boost biological productivity and shape the distribution of marine species. The study provides a valuable foundation for the further development of a digital twin of the ocean.
Located about 600 kilometers off the coast of West Africa, the Cape Verde Archipelago is a biodiversity hotspot in the middle of the open Atlantic. Despite the generally oligotrophic environment, the waters around the islands are teeming with whales, dolphins, and large schools of fish. Now, for the first time, researchers led by GEOMAR Helmholtz Centre for Ocean Research Kiel have explained in detail why these islands are so biologically rich: Small-scale physical processes – such as ocean eddies, tides, and wind – create a mosaic of microhabitats, each with its own characteristics. These dynamic conditions form the foundation for the region’s exceptional marine biodiversity.
Two Decades of Interdisciplinary Data
The study is based on an exceptionally rich dataset, including results from 34 research expeditions, measurements by autonomous underwater gliders, satellite observations, and data from long-term ocean moorings. The team combined physical, chemical, and biological parameters to uncover relationships between currents, nutrient availability, and species composition.
“Only by combining all of these different data sources were we able to identify patterns that would have remained invisible using physical data alone,” says first author Dr Florian Schütte, Assistant Professor of Physical Oceanography at GEOMAR. The findings not only offer new insights into the ecosystem, but also lay the groundwork for digital tools such as coupled ecosystem models or even a Digital Twin of the Ocean – a virtual model that integrates massive interdisciplinary datasets. “What we did here is essentially the core idea of a digital twin: bringing together multiple perspectives to understand the system as a whole,” Schütte explains.
Three Key Processes Bring Nutrients to the Surface
From the extensive dataset, the researchers identified three physical mechanisms that drive the upward transport of nitrate – the key limiting nutrient for phytoplankton growth in the Atlantic – from deeper layers to the surface, where it fuels biological productivity:
1. Wind-Driven Island Wakes:
The first mechanism involves “island wakes” – swirling wind patterns that form when the steady northeast trade winds are deflected by the high volcanic peaks of Santo Antão and Fogo. These wind distortions create intense local shear zones that, in turn, generate small but highly productive water eddies. These eddies enhance vertical mixing and nutrient transport in the water column.
2. Mesoscale Ocean Eddies:
The second process involves large-scale ocean eddies – so-called “mesoscale eddies” with diameters of up to 120 kilometers. These features regularly form off the West African coast, where they trap cold, nutrient-rich, and fresher water, carrying it westward toward the Cape Verde Islands. When these eddies encounter islands or shallow waters, they release their nutrient-rich cores and enhance local vertical mixing.
3. Internal Tidal Waves:
The third mechanism results from the interaction of tides with the steep underwater topography of the islands. The Cape Verde Archipelago sits in a deep-sea basin (the Cape Verde Basin) with depths of 3,000 to 4,000 meters. Here, regular tidal flows are disrupted by seamounts and island slopes, generating so-called internal tidal waves. These waves oscillate within ocean layers of differing densities and can travel long distances – or break when encountering steep slopes or shallows, much like surface waves breaking on a beach. When internal waves break, they release significant energy, dramatically increasing vertical mixing. This effect is especially strong south of Santo Antão, where GEOMAR recorded the highest mixing rates ever measured – accompanied by flow speeds several times higher than the original deep-sea tidal current.
The Key Insight: Physics Determines Who Lives Where
“All of these processes bring nitrate into the sunlit surface layer, where it stimulates phytoplankton growth – the foundation of all marine life,” explains Dr Schütte. These productive zones exhibit up to ten times more zooplankton biomass, higher fish catches, and more whale sightings. Even annual catch volumes of mackerel and tuna in the Cape Verde region strongly correlate with the strength of these small-scale physical processes and associated chlorophyll levels.
But the study’s key finding goes beyond productivity: It shows that not only the quantity of life, but also the type of organisms present, depends on the underlying physical dynamics. Zooplankton communities differ markedly between regions dominated by tidal mixing, wind-driven island wakes, or large ocean eddies – and these differences appear to propagate up the food chain to fish and marine mammals.
“Where tides dominate, we find different animals than in areas influenced by wind or eddies,” says Schütte. “What used to seem like chaotic variety now shows recognizable patterns. We're beginning to structure the ocean – and understand how biodiversity emerges.”
Relevance for Marine Conservation and Sustainable Use
For the first time, the study reveals in detail how marine biodiversity around the Cape Verde Islands is shaped by physical ocean processes and underwater topography. This holistic view provides a crucial foundation for understanding the entire ecosystem – from physical drivers to microscopic algae, fish, and whales.
Such a systemic perspective is especially important for marine conservation and sustainable fisheries management. Until now, many fishery decisions have relied primarily on catch statistics. This study shows that forward-looking ocean monitoring requires more: interdisciplinary data collection that captures physical, chemical, and biological processes – ideally combined with satellite data and long-term observations on site.
Schütte, F., Hans, A.C., Schulz, M., Hummels, R., Assokpa, O., Brandt, P., Kiko, R., Körtzinger, A., Fiedler, B., Fischer, T., Rodrigues, E., Hoving, H-J., Hauss, H. (2025). Linking physical processes to biological responses: Interdisciplinary observational insights into the enhanced biological productivity of the Cape Verde Archipelago, Progress in Oceanography, 235, 103479.
https://doi.org/10.1016/j.pocean.2025.103479
http://www.geomar.de/n9879 Images available for download
Video: Long-term ocean observatory off Cabo Verde
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