Influence of African Dust on Ocean-atmosphere Variability in the Tropical Atlantic

The dominant source of coupled ocean–atmosphere variability in the tropical Atlantic is the so-called Atlantic Meridional Mode. This mode of variability is characterized by an interhemispheric gradient in sea surface temperatures and by oscillations in the strength of surface winds that cross the Equator, thereby reinforcing sea surface temperature anomalies. The Atlantic Meridional Mode is thermodynamically damped and must receive external forcing to persist as observed. However, it is not known which external forcing factors have excited the Atlantic Meridional Mode in the historical record. Here we present simulations with an ocean general circulation model that is forced by a record of surface radiation from anomalous dust concentrations in the atmosphere, reconstructed from a coral proxy and satellite retrievals. We show that the Atlantic Meridional Mode is excited by variability in African dust outbreaks on interannual to decadal timescales. Our analysis indicates that sea surface temperature anomalies resulting from the aerosol direct effect persist in time through the positive ocean–atmosphere feedback that defines the Atlantic Meridional Mode. We conclude that on interannual to decadal timescales, the state of the tropical Atlantic ocean is directly tied to dust emissions over West Africa, which in turn are linked to land-use change.

Evan, A. T., G. R. Foltz, D. Zhang and D. J. Vimont (2011) Influence of African dust on ocean-atmosphere variability in the tropical Atlantic, Nature Geoscience, 4, 762–765, doi:10.1038/ngeo1276.