Present-day Saharan dust fluxes across the Atlantic Ocean

Mineral dust plays an important role in the ocean’s carbon cycle through the input of nutrients and metals which potentially fertilise phytoplankton, and by ballasting organic matter from the surface ocean to the deep sea floor. In addition, mineral dust feeds back on climate through many different pathways like changing the radiative balance of the atmosphere, by stimulating cloud formation, dampening hurricane formation and by changing the earth’s albedo. Because open-ocean dust-flux measurements are either based on shipboard- or sediment-trap data, they are biased by interpolation and extrapolation of point observations in space and time. Alternatively, dust-flux estimations can be made using satellite observations, but these are often hampered by the presence of clouds. For these reasons we have been studying Saharan dust along a Transatlantic transect between northwest Africa and the Caribbean, focussing on temporal and spatial variability of dust-deposition fluxes and how these are reflected in terms of dust particle size and composition. One important finding deals with the deposition of Saharan dust by rain, which seems to be an important way to make nutrients available to phytoplankton living in the surface ocean. Nutrient-release bottle experiments in ambient sea water carried out along the same transect demonstrate how wet deposition of Saharan dust increases the release of both macro- (P, Si) and micronutrients (Fe) up to an order-of-magnitude as opposed to dry deposition. Rain-amplified bioavailability of these nutrients may well be the key to increased surface-ocean productivity in the remote and oligotrophic parts of the oceans and, potentially, also continental ecosystems. See: www.nioz.nl/dust