Transatlantic fluxes of Saharan dust

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 floor1. Because open-ocean dust-flux measurements are either based on shipboard**2- or sediment-trap data**1, they are biased by interpolation and extrapolation of point observations in space and time. Alternatively, dust-flux estimations can be made using satellite observations**3, but these are often hampered by the presence of clouds. Here, we present a two-year time series of sediment-trap dust-deposition fluxes directly below the core of the Saharan dust plume along a transatlantic array at 12oN, which shows the spatial and temporal evolution of Saharan-dust deposition across the Atlantic Ocean. We demonstrate that most of the dust deposited in the Atlantic Ocean is washed out of the atmosphere by summer rains. These field data are corroborated by comprehensive earth system model (CESM) dust-deposition data across the same transatlantic transect. In addition, 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**4.