Biogeochemistry and Ecology of Oxygen Depleted Eddies in the Eastern Tropical Atlantic
The recent discovery of isolated low oxygen (O2) water masses in the generally well ventilated open ocean region near the Cape Verde Archipelago changed our understanding of oceanic processes in this area. The eastern tropical North Atlantic (ETNA) is characterized by a highly productive coastal upwelling system off northwest Africa, enhanced Saharan dust deposition, and a moderate O2 minimum zone (OMZ) with lowest O2 concentrations just under 40 μmol/kg. Current understanding is that the ETNA OMZ has been expanding over the past decades both in terms of vertical extent and intensity . Nevertheless, the recently observed exceptionally low O2 concentrations just below the mixed layer ranging from hypoxic (<20 μmol/kg) to even anoxic (<1 μmol/kg) conditions have never been reported before for the ETNA. These O2 depleted isolated water masses were attributed to mesoscale eddies which originated in the highly productive coastal Mauritanian upwelling and propagated westwards. We propose a multi-facetted interdisciplinary field study in the eastern tropical North Atlantic to investigate biogeochemical and ecological processes in recently discovered eddies that entail unexpected subsurface anoxia and hypoxia in the open ocean.
