Impact of cyclonic eddies on organic matter fate in the eastern tropical North Atlantic Ocean
The Eastern Tropical North Atlantic Ocean (ETNA) includes the oligotrophic waters of the Atlantic Gyre and the productive waters of the Canary Current system off Northwest Africa, where upwelling of nutrient-rich waters stimulates primary productivity. The offshore waters of the ETNA are predominantly heterotrophic, as the consumption of organic matter in the euphotic zone is greater than its production. In the ETNA, phytoplankton and bacteria compete for access to inorganic nutrients to produce and degrade organic matter. Mesoscale eddies (10 - 100 km) are ubiquitous features connecting highly productive eastern boundary upwelling system to their adjacent oligotrophic Gyres. Eddies are vectors of organic matter supply that maintain heterotrophy, but they are also responsible for local variability in the balance of trophic metabolism (autotrophy/heterotrophy) as their swirling motion impact water productivity. Eddies influence the stratification of the water column by lifting deep water rich in inorganic nutrients to the surface (upwelling) or by bringing nutrient-poor surface water to the depths (downwelling). In the Canary Current system, coastal upwelling promotes eddy formation. How phytoplankton and heterotrophic bacteria respond to eddy-induced sub-mesoscale (<10 km) disturbances is not yet well defined. In this regard, this thesis is part of the REEBUS (Role of Eddies in the Carbon Pump of Eastern Boundary Upwelling Systems) project, which aims to study how oceanic eddies affect the physical, biogeochemical and biological properties of ETNA waters. The data included in this thesis contribute to a better understanding of the sub-mesoscale impacts of cyclonic eddies on the biogeochemistry and fate of organic matter in the ocean.