Seasonal impact of mineral dust on deep-ocean particle flux in the eastern subtropical Atlantic Ocean

Abstract

Seasonal lithogenic particle and Al fluxes were obtained from a deep-ocean sediment trap deployment during 1992 and 1993 off NW Africa, and were compared concurrently with atmospheric Al concentrations and two-dimensional backward trajectories of windfields from two barometric levels in the lower and mid troposphere. Marine Al fluxes, lithogenic particle fluxes and grain size distributions in the area were found to be directly linked to airmass pathways and surface mineral aerosol concentrations. At 1000 m water depth, highest Al fluxes (10.77 mg m −2 day −1), lithogenic particle fluxes (99.25 mg m −2 day −1) and smallest mean grain sizes (11.9 μm) occurred during the winter and spring season, concurrent with highest atmospheric dust load and Al-concentrations (15 300 ng m −3) in the lower troposphere. A strong seasonal change of the main atmospheric dust transport from low altitude winds during winter/spring to higher altitudes during summer is clearly reflected at depth by a significant coarsening of mean grain sizes (18.6 μm) and lowest Al (0.81 mg m −2 day −1) and lithogenic particle fluxes (11.3 mg m −2 day −1) found in the sediment traps. The comparison of marine, atmospheric and model derived data used within this study highlights the close temporal coupling between atmospheric dust transport and the deep-ocean particle stock.