Linking physical processes to biological responses: Interdisciplinary observational insights into the enhanced biological productivity of the Cape Verde Archipelago

The Cape Verde Archipelago (CVA) is a hotspot of biological productivity in the oligotrophic central North Atlantic, supporting a highly diverse ecosystem. Twenty years of interdisciplinary observational data are used to investigate the primary physical processes driving this productivity and their impacts on the composition of biological life across the food web of the CVA. Three dominant physical processes are identified: I. Atmospheric forced island wakes: Wind interactions with the topography of Santo Antão and Fogo generate local wind shear, creating surface-intensified, productive eddy fields that extend several island diameters downstream. II. Interaction of remotely generated mesoscale eddies with the CVA: Nitrate-rich eddies generated off the coast of West Africa interact with the CVA by colliding with the eastern islands, or by passing near shallow bathymetry. This interaction enhances submesoscale activity, likely driven by unbalanced mesoscale flow, leading to hotspots of vertical advection and mixing. Our observations indicate, in addition, interactions between passing eddies and island-induced processes, such as an elevated internal wave field and wind curl in lee of the islands. This results in up to a tenfold increase in mixing within near-island eddies. III. Interactions of tidal flows and internal waves with the CVA: Internal wave breaking at specific hotspots, such as south of Santo Antão, leads to elevated vertical mixing rates, up to 1000 times higher than at reference points. The mean internal wave field in the CVA is over twice as energetic as in the open ocean, and even stronger at distinct hotspots. These three physical processes, although different in nature, all enhance upward nitrate flux, thereby promoting significantly higher chlorophyll concentrations. This, in turn, forms the foundation of the local pelagic food web, including mesozooplankton and micronekton, such as mesopelagic fishes, whose abundance increase three- to tenfold at these local hotspots. The composition of the biological communities is highly diverse and varies across different regions and physical processes. Annual landings of mackerel and tuna on the CVA, as well as the abundance of humpback whales, are positively correlated with annual mean chlorophyll concentrations. Overall, our study reveals a strong correlation between nitrate supply to the euphotic zone, driven by various physical processes, and species abundance throughout the food web, extending to large predators. These findings underscore the crucial role of local physical processes in shaping the structure of marine communities from lower to higher trophic levels, explaining biological diversity in the marine environment of the CVA and beyond.