Iron, a necessary micronutrient used during primary production in the ocean, enters the tropical North Atlantic through various external sources including river runoff, atmospheric dust, and continental margins, but deposition of atmospheric dust is the primary source of this element to this region. However, despite seasonal fluctuation in the magnitude and path of atmospheric dust delivery, persistent depletion of surface nutrients and moderately high ocean color indicates that other source(s) are providing iron to this area. Scientists from Woods Hole Oceanographic Institute plan to test the hypothesis that the continental margin of northwest Africa provides a significant subsurface supply of iron to the eastern tropical Atlantic that supplements dust. To test this hypothesis, the principal investigators would use a novel combination of measurements (i.e., synchrotron x-ray analysis of particulate iron, radium isotopes, 234Th profiles) during a wintertime visit to the new Tropical Eastern North Atlantic Time-Series Observatory (TENATSO) near Cape Verde, located in the eastern tropical Atlantic about 850 km downstream of Mauritanian coastal upwelling, and a summertime cross-shelf transect from the Mauritanian coast to TENATSO with a scientist from Massachusetts Institute of Technology. It is anticipated that the cross shelf transect and the proposed measurements would allow them to determine the importance of lateral transport versus dust inputs and subsurface remineralization as iron sources to the surface ocean.
As regards broader impacts, the research would provide new insight into the importance of lateral sources of bioavailable iron to the tropical North Atlantic. Scientists from Woods Hole Oceanographic Institution plan to collaborate with those in the Cape Verde Islands, train the researchers in how to determine thorium, radium, and iron, and disseminate results from the study via presentations at the Instituto National de Desenvolvimento das Pescas.
